LCOV - app.info - other-licenses/snappy/src/snappy.cc

LCOV - code coverage report
| Current view: | directory - other-licenses/snappy/src - snappy.cc (source / functions) |  | Found | Hit | Coverage |
| Test: | app.info | Lines: | 424 | 289 | 68.2 %
| Date: | 2012-06-02 | Functions: | 46 | 31 | 67.4 %

           1                 : // Copyright 2005 Google Inc. All Rights Reserved.
           2                 : //
           3                 : // Redistribution and use in source and binary forms, with or without
           4                 : // modification, are permitted provided that the following conditions are
           5                 : // met:
           6                 : //
           7                 : //     * Redistributions of source code must retain the above copyright
           8                 : // notice, this list of conditions and the following disclaimer.
           9                 : //     * Redistributions in binary form must reproduce the above
          10                 : // copyright notice, this list of conditions and the following disclaimer
          11                 : // in the documentation and/or other materials provided with the
          12                 : // distribution.
          13                 : //     * Neither the name of Google Inc. nor the names of its
          14                 : // contributors may be used to endorse or promote products derived from
          15                 : // this software without specific prior written permission.
          16                 : //
          17                 : // THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
          18                 : // "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
          19                 : // LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
          20                 : // A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
          21                 : // OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
          22                 : // SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
          23                 : // LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
          24                 : // DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
          25                 : // THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
          26                 : // (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
          27                 : // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
          28                 :
          29                 : #include "snappy.h"
          30                 : #include "snappy-internal.h"
          31                 : #include "snappy-sinksource.h"
          32                 :
          33                 : #include <stdio.h>
          34                 :
          35                 : #include <algorithm>
          36                 : #include <string>
          37                 : #include <vector>
          38                 :
          39                 :
          40                 : namespace snappy {
          41                 :
          42                 : // Any hash function will produce a valid compressed bitstream, but a good
          43                 : // hash function reduces the number of collisions and thus yields better
          44                 : // compression for compressible input, and more speed for incompressible
          45                 : // input. Of course, it doesn't hurt if the hash function is reasonably fast
          46                 : // either, as it gets called a lot.
          47           35465 : static inline uint32 HashBytes(uint32 bytes, int shift) {
          48           35465 :   uint32 kMul = 0x1e35a7bd;
          49           35465 :   return (bytes * kMul) >> shift;
          50                 : }
          51           31957 : static inline uint32 Hash(const char* p, int shift) {
          52           31957 :   return HashBytes(UNALIGNED_LOAD32(p), shift);
          53                 : }
          54                 :
          55            3674 : size_t MaxCompressedLength(size_t source_len) {
          56                 :   // Compressed data can be defined as:
          57                 :   //    compressed := item* literal*
          58                 :   //    item       := literal* copy
          59                 :   //
          60                 :   // The trailing literal sequence has a space blowup of at most 62/60
          61                 :   // since a literal of length 60 needs one tag byte + one extra byte
          62                 :   // for length information.
          63                 :   //
          64                 :   // Item blowup is trickier to measure.  Suppose the "copy" op copies
          65                 :   // 4 bytes of data.  Because of a special check in the encoding code,
          66                 :   // we produce a 4-byte copy only if the offset is < 65536.  Therefore
          67                 :   // the copy op takes 3 bytes to encode, and this type of item leads
          68                 :   // to at most the 62/60 blowup for representing literals.
          69                 :   //
          70                 :   // Suppose the "copy" op copies 5 bytes of data.  If the offset is big
          71                 :   // enough, it will take 5 bytes to encode the copy op.  Therefore the
          72                 :   // worst case here is a one-byte literal followed by a five-byte copy.
          73                 :   // I.e., 6 bytes of input turn into 7 bytes of "compressed" data.
          74                 :   //
          75                 :   // This last factor dominates the blowup, so the final estimate is:
          76            3674 :   return 32 + source_len + source_len/6;
          77                 : }
          78                 :
          79                 : enum {
          80                 :   LITERAL = 0,
          81                 :   COPY_1_BYTE_OFFSET = 1,  // 3 bit length + 3 bits of offset in opcode
          82                 :   COPY_2_BYTE_OFFSET = 2,
          83                 :   COPY_4_BYTE_OFFSET = 3
          84                 : };
          85                 :
          86                 : // Copy "len" bytes from "src" to "op", one byte at a time.  Used for
          87                 : // handling COPY operations where the input and output regions may
          88                 : // overlap.  For example, suppose:
          89                 : //    src    == "ab"
          90                 : //    op     == src + 2
          91                 : //    len    == 20
          92                 : // After IncrementalCopy(src, op, len), the result will have
          93                 : // eleven copies of "ab"
          94                 : //    ababababababababababab
          95                 : // Note that this does not match the semantics of either memcpy()
          96                 : // or memmove().
          97               8 : static inline void IncrementalCopy(const char* src, char* op, int len) {
          98               8 :   DCHECK_GT(len, 0);
          99              93 :   do {
         100              93 :     *op++ = *src++;
         101                 :   } while (--len > 0);
         102               8 : }
         103                 :
         104                 : // Equivalent to IncrementalCopy except that it can write up to ten extra
         105                 : // bytes after the end of the copy, and that it is faster.
         106                 : //
         107                 : // The main part of this loop is a simple copy of eight bytes at a time until
         108                 : // we've copied (at least) the requested amount of bytes.  However, if op and
         109                 : // src are less than eight bytes apart (indicating a repeating pattern of
         110                 : // length < 8), we first need to expand the pattern in order to get the correct
         111                 : // results. For instance, if the buffer looks like this, with the eight-byte
         112                 : // <src> and <op> patterns marked as intervals:
         113                 : //
         114                 : //    abxxxxxxxxxxxx
         115                 : //    [------]           src
         116                 : //      [------]         op
         117                 : //
         118                 : // a single eight-byte copy from <src> to <op> will repeat the pattern once,
         119                 : // after which we can move <op> two bytes without moving <src>:
         120                 : //
         121                 : //    ababxxxxxxxxxx
         122                 : //    [------]           src
         123                 : //        [------]       op
         124                 : //
         125                 : // and repeat the exercise until the two no longer overlap.
         126                 : //
         127                 : // This allows us to do very well in the special case of one single byte
         128                 : // repeated many times, without taking a big hit for more general cases.
         129                 : //
         130                 : // The worst case of extra writing past the end of the match occurs when
         131                 : // op - src == 1 and len == 1; the last copy will read from byte positions
         132                 : // [0..7] and write to [4..11], whereas it was only supposed to write to
         133                 : // position 1. Thus, ten excess bytes.
         134                 :
         135                 : namespace {
         136                 :
         137                 : const int kMaxIncrementCopyOverflow = 10;
         138                 :
         139                 : }  // namespace
         140                 :
         141             999 : static inline void IncrementalCopyFastPath(const char* src, char* op, int len) {
         142            4078 :   while (op - src < 8) {
         143            2080 :     UNALIGNED_STORE64(op, UNALIGNED_LOAD64(src));
         144            2080 :     len -= op - src;
         145            2080 :     op += op - src;
         146                 :   }
         147            2997 :   while (len > 0) {
         148             999 :     UNALIGNED_STORE64(op, UNALIGNED_LOAD64(src));
         149             999 :     src += 8;
         150             999 :     op += 8;
         151             999 :     len -= 8;
         152                 :   }
         153             999 : }
         154                 :
         155            3066 : static inline char* EmitLiteral(char* op,
         156                 :                                 const char* literal,
         157                 :                                 int len,
         158                 :                                 bool allow_fast_path) {
         159            3066 :   int n = len - 1;      // Zero-length literals are disallowed
         160            3066 :   if (n < 60) {
         161                 :     // Fits in tag byte
         162            3066 :     *op++ = LITERAL | (n << 2);
         163                 :
         164                 :     // The vast majority of copies are below 16 bytes, for which a
         165                 :     // call to memcpy is overkill. This fast path can sometimes
         166                 :     // copy up to 15 bytes too much, but that is okay in the
         167                 :     // main loop, since we have a bit to go on for both sides:
         168                 :     //
         169                 :     //   - The input will always have kInputMarginBytes = 15 extra
         170                 :     //     available bytes, as long as we're in the main loop, and
         171                 :     //     if not, allow_fast_path = false.
         172                 :     //   - The output will always have 32 spare bytes (see
         173                 :     //     MaxCompressedLength).
         174            3066 :     if (allow_fast_path && len <= 16) {
         175             831 :       UNALIGNED_STORE64(op, UNALIGNED_LOAD64(literal));
         176             831 :       UNALIGNED_STORE64(op + 8, UNALIGNED_LOAD64(literal + 8));
         177             831 :       return op + len;
         178                 :     }
         179                 :   } else {
         180                 :     // Encode in upcoming bytes
         181               0 :     char* base = op;
         182               0 :     int count = 0;
         183               0 :     op++;
         184               0 :     while (n > 0) {
         185               0 :       *op++ = n & 0xff;
         186               0 :       n >>= 8;
         187               0 :       count++;
         188                 :     }
         189               0 :     assert(count >= 1);
         190               0 :     assert(count <= 4);
         191               0 :     *base = LITERAL | ((59+count) << 2);
         192                 :   }
         193            2235 :   memcpy(op, literal, len);
         194            2235 :   return op + len;
         195                 : }
         196                 :
         197            1657 : static inline char* EmitCopyLessThan64(char* op, size_t offset, int len) {
         198            1657 :   DCHECK_LE(len, 64);
         199            1657 :   DCHECK_GE(len, 4);
         200            1657 :   DCHECK_LT(offset, 65536);
         201                 :
         202            1657 :   if ((len < 12) && (offset < 2048)) {
         203            1600 :     size_t len_minus_4 = len - 4;
         204            1600 :     assert(len_minus_4 < 8);            // Must fit in 3 bits
         205            1600 :     *op++ = COPY_1_BYTE_OFFSET | ((len_minus_4) << 2) | ((offset >> 8) << 5);
         206            1600 :     *op++ = offset & 0xff;
         207                 :   } else {
         208              57 :     *op++ = COPY_2_BYTE_OFFSET | ((len-1) << 2);
         209              57 :     LittleEndian::Store16(op, offset);
         210              57 :     op += 2;
         211                 :   }
         212            1657 :   return op;
         213                 : }
         214                 :
         215            1657 : static inline char* EmitCopy(char* op, size_t offset, int len) {
         216                 :   // Emit 64 byte copies but make sure to keep at least four bytes reserved
         217            3314 :   while (len >= 68) {
         218               0 :     op = EmitCopyLessThan64(op, offset, 64);
         219               0 :     len -= 64;
         220                 :   }
         221                 :
         222                 :   // Emit an extra 60 byte copy if have too much data to fit in one copy
         223            1657 :   if (len > 64) {
         224               0 :     op = EmitCopyLessThan64(op, offset, 60);
         225               0 :     len -= 60;
         226                 :   }
         227                 :
         228                 :   // Emit remainder
         229            1657 :   op = EmitCopyLessThan64(op, offset, len);
         230            1657 :   return op;
         231                 : }
         232                 :
         233                 :
         234            1970 : bool GetUncompressedLength(const char* start, size_t n, size_t* result) {
         235            1970 :   uint32 v = 0;
         236            1970 :   const char* limit = start + n;
         237            1970 :   if (Varint::Parse32WithLimit(start, limit, &v) != NULL) {
         238            1970 :     *result = v;
         239            1970 :     return true;
         240                 :   } else {
         241               0 :     return false;
         242                 :   }
         243                 : }
         244                 :
         245                 : namespace internal {
         246            1837 : uint16* WorkingMemory::GetHashTable(size_t input_size, int* table_size) {
         247                 :   // Use smaller hash table when input.size() is smaller, since we
         248                 :   // fill the table, incurring O(hash table size) overhead for
         249                 :   // compression, and if the input is short, we won't need that
         250                 :   // many hash table entries anyway.
         251                 :   assert(kMaxHashTableSize >= 256);
         252            1837 :   size_t htsize = 256;
         253            3674 :   while (htsize < kMaxHashTableSize && htsize < input_size) {
         254               0 :     htsize <<= 1;
         255                 :   }
         256            1837 :   CHECK_EQ(0, htsize & (htsize - 1)) << ": must be power of two";
         257            1837 :   CHECK_LE(htsize, kMaxHashTableSize) << ": hash table too large";
         258                 :
         259                 :   uint16* table;
         260            1837 :   if (htsize <= ARRAYSIZE(small_table_)) {
         261            1837 :     table = small_table_;
         262                 :   } else {
         263               0 :     if (large_table_ == NULL) {
         264               0 :       large_table_ = new uint16[kMaxHashTableSize];
         265                 :     }
         266               0 :     table = large_table_;
         267                 :   }
         268                 :
         269            1837 :   *table_size = htsize;
         270            1837 :   memset(table, 0, htsize * sizeof(*table));
         271            1837 :   return table;
         272                 : }
         273                 : }  // end namespace internal
         274                 :
         275                 : // For 0 <= offset <= 4, GetUint32AtOffset(UNALIGNED_LOAD64(p), offset) will
         276                 : // equal UNALIGNED_LOAD32(p + offset).  Motivation: On x86-64 hardware we have
         277                 : // empirically found that overlapping loads such as
         278                 : //  UNALIGNED_LOAD32(p) ... UNALIGNED_LOAD32(p+1) ... UNALIGNED_LOAD32(p+2)
         279                 : // are slower than UNALIGNED_LOAD64(p) followed by shifts and casts to uint32.
         280            4820 : static inline uint32 GetUint32AtOffset(uint64 v, int offset) {
         281            4820 :   DCHECK(0 <= offset && offset <= 4) << offset;
         282            4820 :   return v >> (LittleEndian::IsLittleEndian() ? 8 * offset : 32 - 8 * offset);
         283                 : }
         284                 :
         285                 : // Flat array compression that does not emit the "uncompressed length"
         286                 : // prefix. Compresses "input" string to the "*op" buffer.
         287                 : //
         288                 : // REQUIRES: "input" is at most "kBlockSize" bytes long.
         289                 : // REQUIRES: "op" points to an array of memory that is at least
         290                 : // "MaxCompressedLength(input.size())" in size.
         291                 : // REQUIRES: All elements in "table[0..table_size-1]" are initialized to zero.
         292                 : // REQUIRES: "table_size" is a power of two
         293                 : //
         294                 : // Returns an "end" pointer into "op" buffer.
         295                 : // "end - op" is the compressed size of "input".
         296                 : namespace internal {
         297            1837 : char* CompressFragment(const char* input,
         298                 :                        size_t input_size,
         299                 :                        char* op,
         300                 :                        uint16* table,
         301                 :                        const int table_size) {
         302                 :   // "ip" is the input pointer, and "op" is the output pointer.
         303            1837 :   const char* ip = input;
         304            1837 :   CHECK_LE(input_size, kBlockSize);
         305            1837 :   CHECK_EQ(table_size & (table_size - 1), 0) << ": table must be power of two";
         306            1837 :   const int shift = 32 - Bits::Log2Floor(table_size);
         307            1837 :   DCHECK_EQ(static_cast<int>(kuint32max >> shift), table_size - 1);
         308            1837 :   const char* ip_end = input + input_size;
         309            1837 :   const char* base_ip = ip;
         310                 :   // Bytes in [next_emit, ip) will be emitted as literal bytes.  Or
         311                 :   // [next_emit, ip_end) after the main loop.
         312            1837 :   const char* next_emit = ip;
         313                 :
         314            1837 :   const size_t kInputMarginBytes = 15;
         315            1837 :   if (PREDICT_TRUE(input_size >= kInputMarginBytes)) {
         316            1701 :     const char* ip_limit = input + input_size - kInputMarginBytes;
         317                 :
         318            2585 :     for (uint32 next_hash = Hash(++ip, shift); ; ) {
         319            2585 :       DCHECK_LT(next_emit, ip);
         320                 :       // The body of this loop calls EmitLiteral once and then EmitCopy one or
         321                 :       // more times.  (The exception is that when we're close to exhausting
         322                 :       // the input we goto emit_remainder.)
         323                 :       //
         324                 :       // In the first iteration of this loop we're just starting, so
         325                 :       // there's nothing to copy, so calling EmitLiteral once is
         326                 :       // necessary.  And we only start a new iteration when the
         327                 :       // current iteration has determined that a call to EmitLiteral will
         328                 :       // precede the next call to EmitCopy (if any).
         329                 :       //
         330                 :       // Step 1: Scan forward in the input looking for a 4-byte-long match.
         331                 :       // If we get close to exhausting the input then goto emit_remainder.
         332                 :       //
         333                 :       // Heuristic match skipping: If 32 bytes are scanned with no matches
         334                 :       // found, start looking only at every other byte. If 32 more bytes are
         335                 :       // scanned, look at every third byte, etc.. When a match is found,
         336                 :       // immediately go back to looking at every byte. This is a small loss
         337                 :       // (~5% performance, ~0.1% density) for compressible data due to more
         338                 :       // bookkeeping, but for non-compressible data (such as JPEG) it's a huge
         339                 :       // win since the compressor quickly "realizes" the data is incompressible
         340                 :       // and doesn't bother looking for matches everywhere.
         341                 :       //
         342                 :       // The "skip" variable keeps track of how many bytes there are since the
         343                 :       // last match; dividing it by 32 (ie. right-shifting by five) gives the
         344                 :       // number of bytes to move ahead for each iteration.
         345            2585 :       uint32 skip = 32;
         346                 :
         347            2585 :       const char* next_ip = ip;
         348                 :       const char* candidate;
         349           14450 :       do {
         350           15806 :         ip = next_ip;
         351           15806 :         uint32 hash = next_hash;
         352           15806 :         DCHECK_EQ(hash, Hash(ip, shift));
         353           15806 :         uint32 bytes_between_hash_lookups = skip++ >> 5;
         354           15806 :         next_ip = ip + bytes_between_hash_lookups;
         355           15806 :         if (PREDICT_FALSE(next_ip > ip_limit)) {
         356            1356 :           goto emit_remainder;
         357                 :         }
         358           14450 :         next_hash = Hash(next_ip, shift);
         359           14450 :         candidate = base_ip + table[hash];
         360           14450 :         DCHECK_GE(candidate, base_ip);
         361           14450 :         DCHECK_LT(candidate, ip);
         362                 :
         363           14450 :         table[hash] = ip - base_ip;
         364                 :       } while (PREDICT_TRUE(UNALIGNED_LOAD32(ip) !=
         365                 :                             UNALIGNED_LOAD32(candidate)));
         366                 :
         367                 :       // Step 2: A 4-byte match has been found.  We'll later see if more
         368                 :       // than 4 bytes match.  But, prior to the match, input
         369                 :       // bytes [next_emit, ip) are unmatched.  Emit them as "literal bytes."
         370            1229 :       DCHECK_LE(next_emit + 16, ip_end);
         371            1229 :       op = EmitLiteral(op, next_emit, ip - next_emit, true);
         372                 :
         373                 :       // Step 3: Call EmitCopy, and then see if another EmitCopy could
         374                 :       // be our next move.  Repeat until we find no match for the
         375                 :       // input immediately after what was consumed by the last EmitCopy call.
         376                 :       //
         377                 :       // If we exit this loop normally then we need to call EmitLiteral next,
         378                 :       // though we don't yet know how big the literal will be.  We handle that
         379                 :       // by proceeding to the next iteration of the main loop.  We also can exit
         380                 :       // this loop via goto if we get close to exhausting the input.
         381            1229 :       uint64 input_bytes = 0;
         382            1229 :       uint32 candidate_bytes = 0;
         383                 :
         384            1312 :       do {
         385                 :         // We have a 4-byte match at ip, and no need to emit any
         386                 :         // "literal bytes" prior to ip.
         387            1657 :         const char* base = ip;
         388            1657 :         int matched = 4 + FindMatchLength(candidate + 4, ip + 4, ip_end);
         389            1657 :         ip += matched;
         390            1657 :         size_t offset = base - candidate;
         391            1657 :         DCHECK_EQ(0, memcmp(base, candidate, matched));
         392            1657 :         op = EmitCopy(op, offset, matched);
         393                 :         // We could immediately start working at ip now, but to improve
         394                 :         // compression we first update table[Hash(ip - 1, ...)].
         395            1657 :         const char* insert_tail = ip - 1;
         396            1657 :         next_emit = ip;
         397            1657 :         if (PREDICT_FALSE(ip >= ip_limit)) {
         398             345 :           goto emit_remainder;
         399                 :         }
         400            1312 :         input_bytes = UNALIGNED_LOAD64(insert_tail);
         401            1312 :         uint32 prev_hash = HashBytes(GetUint32AtOffset(input_bytes, 0), shift);
         402            1312 :         table[prev_hash] = ip - base_ip - 1;
         403            1312 :         uint32 cur_hash = HashBytes(GetUint32AtOffset(input_bytes, 1), shift);
         404            1312 :         candidate = base_ip + table[cur_hash];
         405            1312 :         candidate_bytes = UNALIGNED_LOAD32(candidate);
         406            1312 :         table[cur_hash] = ip - base_ip;
         407            1312 :       } while (GetUint32AtOffset(input_bytes, 1) == candidate_bytes);
         408                 :
         409             884 :       next_hash = HashBytes(GetUint32AtOffset(input_bytes, 2), shift);
         410             884 :       ++ip;
         411                 :     }
         412                 :   }
         413                 :
         414                 :  emit_remainder:
         415                 :   // Emit the remaining bytes as a literal
         416            1837 :   if (next_emit < ip_end) {
         417            1837 :     op = EmitLiteral(op, next_emit, ip_end - next_emit, false);
         418                 :   }
         419                 :
         420            1837 :   return op;
         421                 : }
         422                 : }  // end namespace internal
         423                 :
         424                 : // Signature of output types needed by decompression code.
         425                 : // The decompression code is templatized on a type that obeys this
         426                 : // signature so that we do not pay virtual function call overhead in
         427                 : // the middle of a tight decompression loop.
         428                 : //
         429                 : // class DecompressionWriter {
         430                 : //  public:
         431                 : //   // Called before decompression
         432                 : //   void SetExpectedLength(size_t length);
         433                 : //
         434                 : //   // Called after decompression
         435                 : //   bool CheckLength() const;
         436                 : //
         437                 : //   // Called repeatedly during decompression
         438                 : //   bool Append(const char* ip, size_t length);
         439                 : //   bool AppendFromSelf(uint32 offset, size_t length);
         440                 : //
         441                 : //   // The difference between TryFastAppend and Append is that TryFastAppend
         442                 : //   // is allowed to read up to <available> bytes from the input buffer,
         443                 : //   // whereas Append is allowed to read <length>.
         444                 : //   //
         445                 : //   // Also, TryFastAppend is allowed to return false, declining the append,
         446                 : //   // without it being a fatal error -- just "return false" would be
         447                 : //   // a perfectly legal implementation of TryFastAppend. The intention
         448                 : //   // is for TryFastAppend to allow a fast path in the common case of
         449                 : //   // a small append.
         450                 : //   //
         451                 : //   // NOTE(user): TryFastAppend must always return decline (return false)
         452                 : //   // if <length> is 61 or more, as in this case the literal length is not
         453                 : //   // decoded fully. In practice, this should not be a big problem,
         454                 : //   // as it is unlikely that one would implement a fast path accepting
         455                 : //   // this much data.
         456                 : //   bool TryFastAppend(const char* ip, size_t available, size_t length);
         457                 : // };
         458                 :
         459                 : // -----------------------------------------------------------------------
         460                 : // Lookup table for decompression code.  Generated by ComputeTable() below.
         461                 : // -----------------------------------------------------------------------
         462                 :
         463                 : // Mapping from i in range [0,4] to a mask to extract the bottom 8*i bits
         464                 : static const uint32 wordmask[] = {
         465                 :   0u, 0xffu, 0xffffu, 0xffffffu, 0xffffffffu
         466                 : };
         467                 :
         468                 : // Data stored per entry in lookup table:
         469                 : //      Range   Bits-used       Description
         470                 : //      ------------------------------------
         471                 : //      1..64   0..7            Literal/copy length encoded in opcode byte
         472                 : //      0..7    8..10           Copy offset encoded in opcode byte / 256
         473                 : //      0..4    11..13          Extra bytes after opcode
         474                 : //
         475                 : // We use eight bits for the length even though 7 would have sufficed
         476                 : // because of efficiency reasons:
         477                 : //      (1) Extracting a byte is faster than a bit-field
         478                 : //      (2) It properly aligns copy offset so we do not need a <<8
         479                 : static const uint16 char_table[256] = {
         480                 :   0x0001, 0x0804, 0x1001, 0x2001, 0x0002, 0x0805, 0x1002, 0x2002,
         481                 :   0x0003, 0x0806, 0x1003, 0x2003, 0x0004, 0x0807, 0x1004, 0x2004,
         482                 :   0x0005, 0x0808, 0x1005, 0x2005, 0x0006, 0x0809, 0x1006, 0x2006,
         483                 :   0x0007, 0x080a, 0x1007, 0x2007, 0x0008, 0x080b, 0x1008, 0x2008,
         484                 :   0x0009, 0x0904, 0x1009, 0x2009, 0x000a, 0x0905, 0x100a, 0x200a,
         485                 :   0x000b, 0x0906, 0x100b, 0x200b, 0x000c, 0x0907, 0x100c, 0x200c,
         486                 :   0x000d, 0x0908, 0x100d, 0x200d, 0x000e, 0x0909, 0x100e, 0x200e,
         487                 :   0x000f, 0x090a, 0x100f, 0x200f, 0x0010, 0x090b, 0x1010, 0x2010,
         488                 :   0x0011, 0x0a04, 0x1011, 0x2011, 0x0012, 0x0a05, 0x1012, 0x2012,
         489                 :   0x0013, 0x0a06, 0x1013, 0x2013, 0x0014, 0x0a07, 0x1014, 0x2014,
         490                 :   0x0015, 0x0a08, 0x1015, 0x2015, 0x0016, 0x0a09, 0x1016, 0x2016,
         491                 :   0x0017, 0x0a0a, 0x1017, 0x2017, 0x0018, 0x0a0b, 0x1018, 0x2018,
         492                 :   0x0019, 0x0b04, 0x1019, 0x2019, 0x001a, 0x0b05, 0x101a, 0x201a,
         493                 :   0x001b, 0x0b06, 0x101b, 0x201b, 0x001c, 0x0b07, 0x101c, 0x201c,
         494                 :   0x001d, 0x0b08, 0x101d, 0x201d, 0x001e, 0x0b09, 0x101e, 0x201e,
         495                 :   0x001f, 0x0b0a, 0x101f, 0x201f, 0x0020, 0x0b0b, 0x1020, 0x2020,
         496                 :   0x0021, 0x0c04, 0x1021, 0x2021, 0x0022, 0x0c05, 0x1022, 0x2022,
         497                 :   0x0023, 0x0c06, 0x1023, 0x2023, 0x0024, 0x0c07, 0x1024, 0x2024,
         498                 :   0x0025, 0x0c08, 0x1025, 0x2025, 0x0026, 0x0c09, 0x1026, 0x2026,
         499                 :   0x0027, 0x0c0a, 0x1027, 0x2027, 0x0028, 0x0c0b, 0x1028, 0x2028,
         500                 :   0x0029, 0x0d04, 0x1029, 0x2029, 0x002a, 0x0d05, 0x102a, 0x202a,
         501                 :   0x002b, 0x0d06, 0x102b, 0x202b, 0x002c, 0x0d07, 0x102c, 0x202c,
         502                 :   0x002d, 0x0d08, 0x102d, 0x202d, 0x002e, 0x0d09, 0x102e, 0x202e,
         503                 :   0x002f, 0x0d0a, 0x102f, 0x202f, 0x0030, 0x0d0b, 0x1030, 0x2030,
         504                 :   0x0031, 0x0e04, 0x1031, 0x2031, 0x0032, 0x0e05, 0x1032, 0x2032,
         505                 :   0x0033, 0x0e06, 0x1033, 0x2033, 0x0034, 0x0e07, 0x1034, 0x2034,
         506                 :   0x0035, 0x0e08, 0x1035, 0x2035, 0x0036, 0x0e09, 0x1036, 0x2036,
         507                 :   0x0037, 0x0e0a, 0x1037, 0x2037, 0x0038, 0x0e0b, 0x1038, 0x2038,
         508                 :   0x0039, 0x0f04, 0x1039, 0x2039, 0x003a, 0x0f05, 0x103a, 0x203a,
         509                 :   0x003b, 0x0f06, 0x103b, 0x203b, 0x003c, 0x0f07, 0x103c, 0x203c,
         510                 :   0x0801, 0x0f08, 0x103d, 0x203d, 0x1001, 0x0f09, 0x103e, 0x203e,
         511                 :   0x1801, 0x0f0a, 0x103f, 0x203f, 0x2001, 0x0f0b, 0x1040, 0x2040
         512                 : };
         513                 :
         514                 : // In debug mode, allow optional computation of the table at startup.
         515                 : // Also, check that the decompression table is correct.
         516                 : #ifndef NDEBUG
         517                 : DEFINE_bool(snappy_dump_decompression_table, false,
         518                 :             "If true, we print the decompression table at startup.");
         519                 :
         520               0 : static uint16 MakeEntry(unsigned int extra,
         521                 :                         unsigned int len,
         522                 :                         unsigned int copy_offset) {
         523                 :   // Check that all of the fields fit within the allocated space
         524               0 :   DCHECK_EQ(extra,       extra & 0x7);          // At most 3 bits
         525               0 :   DCHECK_EQ(copy_offset, copy_offset & 0x7);    // At most 3 bits
         526               0 :   DCHECK_EQ(len,         len & 0x7f);           // At most 7 bits
         527               0 :   return len | (copy_offset << 8) | (extra << 11);
         528                 : }
         529                 :
         530               0 : static void ComputeTable() {
         531                 :   uint16 dst[256];
         532                 :
         533                 :   // Place invalid entries in all places to detect missing initialization
         534               0 :   int assigned = 0;
         535               0 :   for (int i = 0; i < 256; i++) {
         536               0 :     dst[i] = 0xffff;
         537                 :   }
         538                 :
         539                 :   // Small LITERAL entries.  We store (len-1) in the top 6 bits.
         540               0 :   for (unsigned int len = 1; len <= 60; len++) {
         541               0 :     dst[LITERAL | ((len-1) << 2)] = MakeEntry(0, len, 0);
         542               0 :     assigned++;
         543                 :   }
         544                 :
         545                 :   // Large LITERAL entries.  We use 60..63 in the high 6 bits to
         546                 :   // encode the number of bytes of length info that follow the opcode.
         547               0 :   for (unsigned int extra_bytes = 1; extra_bytes <= 4; extra_bytes++) {
         548                 :     // We set the length field in the lookup table to 1 because extra
         549                 :     // bytes encode len-1.
         550               0 :     dst[LITERAL | ((extra_bytes+59) << 2)] = MakeEntry(extra_bytes, 1, 0);
         551               0 :     assigned++;
         552                 :   }
         553                 :
         554                 :   // COPY_1_BYTE_OFFSET.
         555                 :   //
         556                 :   // The tag byte in the compressed data stores len-4 in 3 bits, and
         557                 :   // offset/256 in 5 bits.  offset%256 is stored in the next byte.
         558                 :   //
         559                 :   // This format is used for length in range [4..11] and offset in
         560                 :   // range [0..2047]
         561               0 :   for (unsigned int len = 4; len < 12; len++) {
         562               0 :     for (unsigned int offset = 0; offset < 2048; offset += 256) {
         563               0 :       dst[COPY_1_BYTE_OFFSET | ((len-4)<<2) | ((offset>>8)<<5)] =
         564               0 :         MakeEntry(1, len, offset>>8);
         565               0 :       assigned++;
         566                 :     }
         567                 :   }
         568                 :
         569                 :   // COPY_2_BYTE_OFFSET.
         570                 :   // Tag contains len-1 in top 6 bits, and offset in next two bytes.
         571               0 :   for (unsigned int len = 1; len <= 64; len++) {
         572               0 :     dst[COPY_2_BYTE_OFFSET | ((len-1)<<2)] = MakeEntry(2, len, 0);
         573               0 :     assigned++;
         574                 :   }
         575                 :
         576                 :   // COPY_4_BYTE_OFFSET.
         577                 :   // Tag contents len-1 in top 6 bits, and offset in next four bytes.
         578               0 :   for (unsigned int len = 1; len <= 64; len++) {
         579               0 :     dst[COPY_4_BYTE_OFFSET | ((len-1)<<2)] = MakeEntry(4, len, 0);
         580               0 :     assigned++;
         581                 :   }
         582                 :
         583                 :   // Check that each entry was initialized exactly once.
         584               0 :   CHECK_EQ(assigned, 256);
         585               0 :   for (int i = 0; i < 256; i++) {
         586               0 :     CHECK_NE(dst[i], 0xffff);
         587                 :   }
         588                 :
         589               0 :   if (FLAGS_snappy_dump_decompression_table) {
         590               0 :     printf("static const uint16 char_table[256] = {\n  ");
         591               0 :     for (int i = 0; i < 256; i++) {
         592                 :       printf("0x%04x%s",
         593               0 :              dst[i],
         594               0 :              ((i == 255) ? "\n" : (((i%8) == 7) ? ",\n  " : ", ")));
         595                 :     }
         596               0 :     printf("};\n");
         597                 :   }
         598                 :
         599                 :   // Check that computed table matched recorded table
         600               0 :   for (int i = 0; i < 256; i++) {
         601               0 :     CHECK_EQ(dst[i], char_table[i]);
         602                 :   }
         603               0 : }
         604                 : #endif /* !NDEBUG */
         605                 :
         606                 : // Helper class for decompression
         607                 : class SnappyDecompressor {
         608                 :  private:
         609                 :   Source*       reader_;         // Underlying source of bytes to decompress
         610                 :   const char*   ip_;             // Points to next buffered byte
         611                 :   const char*   ip_limit_;       // Points just past buffered bytes
         612                 :   uint32        peeked_;         // Bytes peeked from reader (need to skip)
         613                 :   bool          eof_;            // Hit end of input without an error?
         614                 :   char          scratch_[5];     // Temporary buffer for PeekFast() boundaries
         615                 :
         616                 :   // Ensure that all of the tag metadata for the next tag is available
         617                 :   // in [ip_..ip_limit_-1].  Also ensures that [ip,ip+4] is readable even
         618                 :   // if (ip_limit_ - ip_ < 5).
         619                 :   //
         620                 :   // Returns true on success, false on error or end of input.
         621                 :   bool RefillTag();
         622                 :
         623                 :  public:
         624            1970 :   explicit SnappyDecompressor(Source* reader)
         625                 :       : reader_(reader),
         626                 :         ip_(NULL),
         627                 :         ip_limit_(NULL),
         628                 :         peeked_(0),
         629            1970 :         eof_(false) {
         630            1970 :   }
         631                 :
         632            1970 :   ~SnappyDecompressor() {
         633                 :     // Advance past any bytes we peeked at from the reader
         634            1970 :     reader_->Skip(peeked_);
         635            1970 :   }
         636                 :
         637                 :   // Returns true iff we have hit the end of the input without an error.
         638            1970 :   bool eof() const {
         639            1970 :     return eof_;
         640                 :   }
         641                 :
         642                 :   // Read the uncompressed length stored at the start of the compressed data.
         643                 :   // On succcess, stores the length in *result and returns true.
         644                 :   // On failure, returns false.
         645            1970 :   bool ReadUncompressedLength(uint32* result) {
         646            1970 :     DCHECK(ip_ == NULL);       // Must not have read anything yet
         647                 :     // Length is encoded in 1..5 bytes
         648            1970 :     *result = 0;
         649            1970 :     uint32 shift = 0;
         650             224 :     while (true) {
         651            2194 :       if (shift >= 32) return false;
         652                 :       size_t n;
         653            2194 :       const char* ip = reader_->Peek(&n);
         654            2194 :       if (n == 0) return false;
         655            2194 :       const unsigned char c = *(reinterpret_cast<const unsigned char*>(ip));
         656            2194 :       reader_->Skip(1);
         657            2194 :       *result |= static_cast<uint32>(c & 0x7f) << shift;
         658            2194 :       if (c < 128) {
         659                 :         break;
         660                 :       }
         661             224 :       shift += 7;
         662                 :     }
         663            1970 :     return true;
         664                 :   }
         665                 :
         666                 :   // Process the next item found in the input.
         667                 :   // Returns true if successful, false on error or end of input.
         668                 :   template <class Writer>
         669            1970 :   void DecompressAllTags(Writer* writer) {
         670            1970 :     const char* ip = ip_;
         671                 :
         672                 :     // We could have put this refill fragment only at the beginning of the loop.
         673                 :     // However, duplicating it at the end of each branch gives the compiler more
         674                 :     // scope to optimize the <ip_limit_ - ip> expression based on the local
         675                 :     // context, which overall increases speed.
         676                 :     #define MAYBE_REFILL() \
         677                 :         if (ip_limit_ - ip < 5) { \
         678                 :           ip_ = ip; \
         679                 :           if (!RefillTag()) return; \
         680                 :           ip = ip_; \
         681                 :         }
         682                 :
         683            1970 :     MAYBE_REFILL();
         684            7461 :     for ( ;; ) {
         685            9431 :       const unsigned char c = *(reinterpret_cast<const unsigned char*>(ip++));
         686                 :
         687            9431 :       if ((c & 0x3) == LITERAL) {
         688            5181 :         size_t literal_length = (c >> 2) + 1u;
         689            5181 :         if (writer->TryFastAppend(ip, ip_limit_ - ip, literal_length)) {
         690            3845 :           DCHECK_LT(literal_length, 61);
         691            3845 :           ip += literal_length;
         692            3845 :           MAYBE_REFILL();
         693            2619 :           continue;
         694                 :         }
         695            1336 :         if (PREDICT_FALSE(literal_length >= 61)) {
         696                 :           // Long literal.
         697               0 :           const size_t literal_length_length = literal_length - 60;
         698               0 :           literal_length =
         699                 :               (LittleEndian::Load32(ip) & wordmask[literal_length_length]) + 1;
         700               0 :           ip += literal_length_length;
         701                 :         }
         702                 :
         703            1336 :         size_t avail = ip_limit_ - ip;
         704            2672 :         while (avail < literal_length) {
         705               0 :           if (!writer->Append(ip, avail)) return;
         706               0 :           literal_length -= avail;
         707               0 :           reader_->Skip(peeked_);
         708                 :           size_t n;
         709               0 :           ip = reader_->Peek(&n);
         710               0 :           avail = n;
         711               0 :           peeked_ = avail;
         712               0 :           if (avail == 0) return;  // Premature end of input
         713               0 :           ip_limit_ = ip + avail;
         714                 :         }
         715            1336 :         if (!writer->Append(ip, literal_length)) {
         716               0 :           return;
         717                 :         }
         718            1336 :         ip += literal_length;
         719            1336 :         MAYBE_REFILL();
         720                 :       } else {
         721            4250 :         const uint32 entry = char_table[c];
         722            4250 :         const uint32 trailer = LittleEndian::Load32(ip) & wordmask[entry >> 11];
         723            4250 :         const uint32 length = entry & 0xff;
         724            4250 :         ip += entry >> 11;
         725                 :
         726                 :         // copy_offset/256 is encoded in bits 8..10.  By just fetching
         727                 :         // those bits, we get copy_offset (since the bit-field starts at
         728                 :         // bit 8).
         729            4250 :         const uint32 copy_offset = entry & 0x700;
         730            4250 :         if (!writer->AppendFromSelf(copy_offset + trailer, length)) {
         731               0 :           return;
         732                 :         }
         733            4250 :         MAYBE_REFILL();
         734                 :       }
         735                 :     }
         736                 :
         737                 : #undef MAYBE_REFILL
         738                 :   }
         739                 : };
         740                 :
         741            3945 : bool SnappyDecompressor::RefillTag() {
         742            3945 :   const char* ip = ip_;
         743            3945 :   if (ip == ip_limit_) {
         744                 :     // Fetch a new fragment from the reader
         745            3940 :     reader_->Skip(peeked_);   // All peeked bytes are used up
         746                 :     size_t n;
         747            3940 :     ip = reader_->Peek(&n);
         748            3940 :     peeked_ = n;
         749            3940 :     if (n == 0) {
         750            1970 :       eof_ = true;
         751            1970 :       return false;
         752                 :     }
         753            1970 :     ip_limit_ = ip + n;
         754                 :   }
         755                 :
         756                 :   // Read the tag character
         757            1975 :   DCHECK_LT(ip, ip_limit_);
         758            1975 :   const unsigned char c = *(reinterpret_cast<const unsigned char*>(ip));
         759            1975 :   const uint32 entry = char_table[c];
         760            1975 :   const uint32 needed = (entry >> 11) + 1;  // +1 byte for 'c'
         761            1975 :   DCHECK_LE(needed, sizeof(scratch_));
         762                 :
         763                 :   // Read more bytes from reader if needed
         764            1975 :   uint32 nbuf = ip_limit_ - ip;
         765            1975 :   if (nbuf < needed) {
         766                 :     // Stitch together bytes from ip and reader to form the word
         767                 :     // contents.  We store the needed bytes in "scratch_".  They
         768                 :     // will be consumed immediately by the caller since we do not
         769                 :     // read more than we need.
         770               0 :     memmove(scratch_, ip, nbuf);
         771               0 :     reader_->Skip(peeked_);  // All peeked bytes are used up
         772               0 :     peeked_ = 0;
         773               0 :     while (nbuf < needed) {
         774                 :       size_t length;
         775               0 :       const char* src = reader_->Peek(&length);
         776               0 :       if (length == 0) return false;
         777               0 :       uint32 to_add = min<uint32>(needed - nbuf, length);
         778               0 :       memcpy(scratch_ + nbuf, src, to_add);
         779               0 :       nbuf += to_add;
         780               0 :       reader_->Skip(to_add);
         781                 :     }
         782               0 :     DCHECK_EQ(nbuf, needed);
         783               0 :     ip_ = scratch_;
         784               0 :     ip_limit_ = scratch_ + needed;
         785            1975 :   } else if (nbuf < 5) {
         786                 :     // Have enough bytes, but move into scratch_ so that we do not
         787                 :     // read past end of input
         788               5 :     memmove(scratch_, ip, nbuf);
         789               5 :     reader_->Skip(peeked_);  // All peeked bytes are used up
         790               5 :     peeked_ = 0;
         791               5 :     ip_ = scratch_;
         792               5 :     ip_limit_ = scratch_ + nbuf;
         793                 :   } else {
         794                 :     // Pass pointer to buffer returned by reader_.
         795            1970 :     ip_ = ip;
         796                 :   }
         797            1975 :   return true;
         798                 : }
         799                 :
         800                 : template <typename Writer>
         801            1970 : static bool InternalUncompress(Source* r,
         802                 :                                Writer* writer,
         803                 :                                uint32 max_len) {
         804                 :   // Read the uncompressed length from the front of the compressed input
         805            3940 :   SnappyDecompressor decompressor(r);
         806            1970 :   uint32 uncompressed_len = 0;
         807            1970 :   if (!decompressor.ReadUncompressedLength(&uncompressed_len)) return false;
         808                 :   // Protect against possible DoS attack
         809            1970 :   if (static_cast<uint64>(uncompressed_len) > max_len) {
         810               0 :     return false;
         811                 :   }
         812                 :
         813            1970 :   writer->SetExpectedLength(uncompressed_len);
         814                 :
         815                 :   // Process the entire input
         816            1970 :   decompressor.DecompressAllTags(writer);
         817            1970 :   return (decompressor.eof() && writer->CheckLength());
         818                 : }
         819                 :
         820               0 : bool GetUncompressedLength(Source* source, uint32* result) {
         821               0 :   SnappyDecompressor decompressor(source);
         822               0 :   return decompressor.ReadUncompressedLength(result);
         823                 : }
         824                 :
         825            1837 : size_t Compress(Source* reader, Sink* writer) {
         826            1837 :   size_t written = 0;
         827            1837 :   size_t N = reader->Available();
         828                 :   char ulength[Varint::kMax32];
         829            1837 :   char* p = Varint::Encode32(ulength, N);
         830            1837 :   writer->Append(ulength, p-ulength);
         831            1837 :   written += (p - ulength);
         832                 :
         833            3674 :   internal::WorkingMemory wmem;
         834            1837 :   char* scratch = NULL;
         835            1837 :   char* scratch_output = NULL;
         836                 :
         837            5511 :   while (N > 0) {
         838                 :     // Get next block to compress (without copying if possible)
         839                 :     size_t fragment_size;
         840            1837 :     const char* fragment = reader->Peek(&fragment_size);
         841            1837 :     DCHECK_NE(fragment_size, 0) << ": premature end of input";
         842            1837 :     const size_t num_to_read = min(N, kBlockSize);
         843            1837 :     size_t bytes_read = fragment_size;
         844                 :
         845            1837 :     size_t pending_advance = 0;
         846            1837 :     if (bytes_read >= num_to_read) {
         847                 :       // Buffer returned by reader is large enough
         848            1837 :       pending_advance = num_to_read;
         849            1837 :       fragment_size = num_to_read;
         850                 :     } else {
         851                 :       // Read into scratch buffer
         852               0 :       if (scratch == NULL) {
         853                 :         // If this is the last iteration, we want to allocate N bytes
         854                 :         // of space, otherwise the max possible kBlockSize space.
         855                 :         // num_to_read contains exactly the correct value
         856               0 :         scratch = new char[num_to_read];
         857                 :       }
         858               0 :       memcpy(scratch, fragment, bytes_read);
         859               0 :       reader->Skip(bytes_read);
         860                 :
         861               0 :       while (bytes_read < num_to_read) {
         862               0 :         fragment = reader->Peek(&fragment_size);
         863               0 :         size_t n = min<size_t>(fragment_size, num_to_read - bytes_read);
         864               0 :         memcpy(scratch + bytes_read, fragment, n);
         865               0 :         bytes_read += n;
         866               0 :         reader->Skip(n);
         867                 :       }
         868               0 :       DCHECK_EQ(bytes_read, num_to_read);
         869               0 :       fragment = scratch;
         870               0 :       fragment_size = num_to_read;
         871                 :     }
         872            1837 :     DCHECK_EQ(fragment_size, num_to_read);
         873                 :
         874                 :     // Get encoding table for compression
         875                 :     int table_size;
         876            1837 :     uint16* table = wmem.GetHashTable(num_to_read, &table_size);
         877                 :
         878                 :     // Compress input_fragment and append to dest
         879            1837 :     const int max_output = MaxCompressedLength(num_to_read);
         880                 :
         881                 :     // Need a scratch buffer for the output, in case the byte sink doesn't
         882                 :     // have room for us directly.
         883            1837 :     if (scratch_output == NULL) {
         884            3674 :       scratch_output = new char[max_output];
         885                 :     } else {
         886                 :       // Since we encode kBlockSize regions followed by a region
         887                 :       // which is <= kBlockSize in length, a previously allocated
         888                 :       // scratch_output[] region is big enough for this iteration.
         889                 :     }
         890            1837 :     char* dest = writer->GetAppendBuffer(max_output, scratch_output);
         891                 :     char* end = internal::CompressFragment(fragment, fragment_size,
         892            1837 :                                            dest, table, table_size);
         893            1837 :     writer->Append(dest, end - dest);
         894            1837 :     written += (end - dest);
         895                 :
         896            1837 :     N -= num_to_read;
         897            1837 :     reader->Skip(pending_advance);
         898                 :   }
         899                 :
         900            1837 :   delete[] scratch;
         901            1837 :   delete[] scratch_output;
         902                 :
         903            1837 :   return written;
         904                 : }
         905                 :
         906                 : // -----------------------------------------------------------------------
         907                 : // Flat array interfaces
         908                 : // -----------------------------------------------------------------------
         909                 :
         910                 : // A type that writes to a flat array.
         911                 : // Note that this is not a "ByteSink", but a type that matches the
         912                 : // Writer template argument to SnappyDecompressor::DecompressAllTags().
         913                 : class SnappyArrayWriter {
         914                 :  private:
         915                 :   char* base_;
         916                 :   char* op_;
         917                 :   char* op_limit_;
         918                 :
         919                 :  public:
         920            1970 :   inline explicit SnappyArrayWriter(char* dst)
         921                 :       : base_(dst),
         922            1970 :         op_(dst) {
         923            1970 :   }
         924                 :
         925            1970 :   inline void SetExpectedLength(size_t len) {
         926            1970 :     op_limit_ = op_ + len;
         927            1970 :   }
         928                 :
         929            1970 :   inline bool CheckLength() const {
         930            1970 :     return op_ == op_limit_;
         931                 :   }
         932                 :
         933            1336 :   inline bool Append(const char* ip, size_t len) {
         934            1336 :     char* op = op_;
         935            1336 :     const size_t space_left = op_limit_ - op;
         936            1336 :     if (space_left < len) {
         937               0 :       return false;
         938                 :     }
         939            1336 :     memcpy(op, ip, len);
         940            1336 :     op_ = op + len;
         941            1336 :     return true;
         942                 :   }
         943                 :
         944            5181 :   inline bool TryFastAppend(const char* ip, size_t available, size_t len) {
         945            5181 :     char* op = op_;
         946            5181 :     const size_t space_left = op_limit_ - op;
         947            5181 :     if (len <= 16 && available >= 16 && space_left >= 16) {
         948                 :       // Fast path, used for the majority (about 95%) of invocations.
         949            3845 :       UNALIGNED_STORE64(op, UNALIGNED_LOAD64(ip));
         950            3845 :       UNALIGNED_STORE64(op + 8, UNALIGNED_LOAD64(ip + 8));
         951            3845 :       op_ = op + len;
         952            3845 :       return true;
         953                 :     } else {
         954            1336 :       return false;
         955                 :     }
         956                 :   }
         957                 :
         958            4250 :   inline bool AppendFromSelf(size_t offset, size_t len) {
         959            4250 :     char* op = op_;
         960            4250 :     const size_t space_left = op_limit_ - op;
         961                 :
         962            4250 :     if (op - base_ <= offset - 1u) {  // -1u catches offset==0
         963               0 :       return false;
         964                 :     }
         965            4250 :     if (len <= 16 && offset >= 8 && space_left >= 16) {
         966                 :       // Fast path, used for the majority (70-80%) of dynamic invocations.
         967            3243 :       UNALIGNED_STORE64(op, UNALIGNED_LOAD64(op - offset));
         968            3243 :       UNALIGNED_STORE64(op + 8, UNALIGNED_LOAD64(op - offset + 8));
         969                 :     } else {
         970            1007 :       if (space_left >= len + kMaxIncrementCopyOverflow) {
         971             999 :         IncrementalCopyFastPath(op - offset, op, len);
         972                 :       } else {
         973               8 :         if (space_left < len) {
         974               0 :           return false;
         975                 :         }
         976               8 :         IncrementalCopy(op - offset, op, len);
         977                 :       }
         978                 :     }
         979                 :
         980            4250 :     op_ = op + len;
         981            4250 :     return true;
         982                 :   }
         983                 : };
         984                 :
         985            1970 : bool RawUncompress(const char* compressed, size_t n, char* uncompressed) {
         986            3940 :   ByteArraySource reader(compressed, n);
         987            1970 :   return RawUncompress(&reader, uncompressed);
         988                 : }
         989                 :
         990            1970 : bool RawUncompress(Source* compressed, char* uncompressed) {
         991            1970 :   SnappyArrayWriter output(uncompressed);
         992            1970 :   return InternalUncompress(compressed, &output, kuint32max);
         993                 : }
         994                 :
         995               0 : bool Uncompress(const char* compressed, size_t n, string* uncompressed) {
         996                 :   size_t ulength;
         997               0 :   if (!GetUncompressedLength(compressed, n, &ulength)) {
         998               0 :     return false;
         999                 :   }
        1000                 :   // Protect against possible DoS attack
        1001               0 :   if ((static_cast<uint64>(ulength) + uncompressed->size()) >
        1002               0 :       uncompressed->max_size()) {
        1003               0 :     return false;
        1004                 :   }
        1005               0 :   STLStringResizeUninitialized(uncompressed, ulength);
        1006               0 :   return RawUncompress(compressed, n, string_as_array(uncompressed));
        1007                 : }
        1008                 :
        1009                 :
        1010                 : // A Writer that drops everything on the floor and just does validation
        1011                 : class SnappyDecompressionValidator {
        1012                 :  private:
        1013                 :   size_t expected_;
        1014                 :   size_t produced_;
        1015                 :
        1016                 :  public:
        1017               0 :   inline SnappyDecompressionValidator() : produced_(0) { }
        1018               0 :   inline void SetExpectedLength(size_t len) {
        1019               0 :     expected_ = len;
        1020               0 :   }
        1021               0 :   inline bool CheckLength() const {
        1022               0 :     return expected_ == produced_;
        1023                 :   }
        1024               0 :   inline bool Append(const char* ip, size_t len) {
        1025               0 :     produced_ += len;
        1026               0 :     return produced_ <= expected_;
        1027                 :   }
        1028               0 :   inline bool TryFastAppend(const char* ip, size_t available, size_t length) {
        1029               0 :     return false;
        1030                 :   }
        1031               0 :   inline bool AppendFromSelf(size_t offset, size_t len) {
        1032               0 :     if (produced_ <= offset - 1u) return false;  // -1u catches offset==0
        1033               0 :     produced_ += len;
        1034               0 :     return produced_ <= expected_;
        1035                 :   }
        1036                 : };
        1037                 :
        1038               0 : bool IsValidCompressedBuffer(const char* compressed, size_t n) {
        1039               0 :   ByteArraySource reader(compressed, n);
        1040               0 :   SnappyDecompressionValidator writer;
        1041               0 :   return InternalUncompress(&reader, &writer, kuint32max);
        1042                 : }
        1043                 :
        1044            1837 : void RawCompress(const char* input,
        1045                 :                  size_t input_length,
        1046                 :                  char* compressed,
        1047                 :                  size_t* compressed_length) {
        1048            3674 :   ByteArraySource reader(input, input_length);
        1049            3674 :   UncheckedByteArraySink writer(compressed);
        1050            1837 :   Compress(&reader, &writer);
        1051                 :
        1052                 :   // Compute how many bytes were added
        1053            1837 :   *compressed_length = (writer.CurrentDestination() - compressed);
        1054            1837 : }
        1055                 :
        1056               0 : size_t Compress(const char* input, size_t input_length, string* compressed) {
        1057                 :   // Pre-grow the buffer to the max length of the compressed output
        1058               0 :   compressed->resize(MaxCompressedLength(input_length));
        1059                 :
        1060                 :   size_t compressed_length;
        1061                 :   RawCompress(input, input_length, string_as_array(compressed),
        1062               0 :               &compressed_length);
        1063               0 :   compressed->resize(compressed_length);
        1064               0 :   return compressed_length;
        1065                 : }
        1066                 :
        1067                 :
        1068            4392 : } // end namespace snappy
        1069                 :

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