| // Copyright 2005 Google Inc. All Rights Reserved. |
| // |
| // Redistribution and use in source and binary forms, with or without |
| // modification, are permitted provided that the following conditions are |
| // met: |
| // |
| // * Redistributions of source code must retain the above copyright |
| // notice, this list of conditions and the following disclaimer. |
| // * Redistributions in binary form must reproduce the above |
| // copyright notice, this list of conditions and the following disclaimer |
| // in the documentation and/or other materials provided with the |
| // distribution. |
| // * Neither the name of Google Inc. nor the names of its |
| // contributors may be used to endorse or promote products derived from |
| // this software without specific prior written permission. |
| // |
| // THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS |
| // "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT |
| // LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR |
| // A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT |
| // OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, |
| // SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT |
| // LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, |
| // DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY |
| // THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT |
| // (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE |
| // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. |
| |
| #include "snappy.h" |
| #include "snappy-internal.h" |
| #include "snappy-sinksource.h" |
| |
| #ifndef SNAPPY_HAVE_SSE2 |
| #if defined(__SSE2__) || defined(_M_X64) || \ |
| (defined(_M_IX86_FP) && _M_IX86_FP >= 2) |
| #define SNAPPY_HAVE_SSE2 1 |
| #else |
| #define SNAPPY_HAVE_SSE2 0 |
| #endif |
| #endif |
| |
| #if SNAPPY_HAVE_SSE2 |
| #include <emmintrin.h> |
| #endif |
| #include <stdio.h> |
| |
| #include <algorithm> |
| #include <string> |
| #include <vector> |
| |
| |
| namespace snappy { |
| |
| using internal::COPY_1_BYTE_OFFSET; |
| using internal::COPY_2_BYTE_OFFSET; |
| using internal::LITERAL; |
| using internal::char_table; |
| using internal::kMaximumTagLength; |
| |
| // Any hash function will produce a valid compressed bitstream, but a good |
| // hash function reduces the number of collisions and thus yields better |
| // compression for compressible input, and more speed for incompressible |
| // input. Of course, it doesn't hurt if the hash function is reasonably fast |
| // either, as it gets called a lot. |
| static inline uint32 HashBytes(uint32 bytes, int shift) { |
| uint32 kMul = 0x1e35a7bd; |
| return (bytes * kMul) >> shift; |
| } |
| static inline uint32 Hash(const char* p, int shift) { |
| return HashBytes(UNALIGNED_LOAD32(p), shift); |
| } |
| |
| size_t MaxCompressedLength(size_t source_len) { |
| // Compressed data can be defined as: |
| // compressed := item* literal* |
| // item := literal* copy |
| // |
| // The trailing literal sequence has a space blowup of at most 62/60 |
| // since a literal of length 60 needs one tag byte + one extra byte |
| // for length information. |
| // |
| // Item blowup is trickier to measure. Suppose the "copy" op copies |
| // 4 bytes of data. Because of a special check in the encoding code, |
| // we produce a 4-byte copy only if the offset is < 65536. Therefore |
| // the copy op takes 3 bytes to encode, and this type of item leads |
| // to at most the 62/60 blowup for representing literals. |
| // |
| // Suppose the "copy" op copies 5 bytes of data. If the offset is big |
| // enough, it will take 5 bytes to encode the copy op. Therefore the |
| // worst case here is a one-byte literal followed by a five-byte copy. |
| // I.e., 6 bytes of input turn into 7 bytes of "compressed" data. |
| // |
| // This last factor dominates the blowup, so the final estimate is: |
| return 32 + source_len + source_len/6; |
| } |
| |
| namespace { |
| |
| void UnalignedCopy64(const void* src, void* dst) { |
| char tmp[8]; |
| memcpy(tmp, src, 8); |
| memcpy(dst, tmp, 8); |
| } |
| |
| void UnalignedCopy128(const void* src, void* dst) { |
| // TODO(alkis): Remove this when we upgrade to a recent compiler that emits |
| // SSE2 moves for memcpy(dst, src, 16). |
| #if SNAPPY_HAVE_SSE2 |
| __m128i x = _mm_loadu_si128(static_cast<const __m128i*>(src)); |
| _mm_storeu_si128(static_cast<__m128i*>(dst), x); |
| #else |
| char tmp[16]; |
| memcpy(tmp, src, 16); |
| memcpy(dst, tmp, 16); |
| #endif |
| } |
| |
| // Copy [src, src+(op_limit-op)) to [op, (op_limit-op)) a byte at a time. Used |
| // for handling COPY operations where the input and output regions may overlap. |
| // For example, suppose: |
| // src == "ab" |
| // op == src + 2 |
| // op_limit == op + 20 |
| // After IncrementalCopySlow(src, op, op_limit), the result will have eleven |
| // copies of "ab" |
| // ababababababababababab |
| // Note that this does not match the semantics of either memcpy() or memmove(). |
| inline char* IncrementalCopySlow(const char* src, char* op, |
| char* const op_limit) { |
| while (op < op_limit) { |
| *op++ = *src++; |
| } |
| return op_limit; |
| } |
| |
| // Copy [src, src+(op_limit-op)) to [op, (op_limit-op)) but faster than |
| // IncrementalCopySlow. buf_limit is the address past the end of the writable |
| // region of the buffer. |
| inline char* IncrementalCopy(const char* src, char* op, char* const op_limit, |
| char* const buf_limit) { |
| // Terminology: |
| // |
| // slop = buf_limit - op |
| // pat = op - src |
| // len = limit - op |
| assert(src < op); |
| assert(op_limit <= buf_limit); |
| // NOTE: The compressor always emits 4 <= len <= 64. It is ok to assume that |
| // to optimize this function but we have to also handle these cases in case |
| // the input does not satisfy these conditions. |
| |
| size_t pattern_size = op - src; |
| // The cases are split into different branches to allow the branch predictor, |
| // FDO, and static prediction hints to work better. For each input we list the |
| // ratio of invocations that match each condition. |
| // |
| // input slop < 16 pat < 8 len > 16 |
| // ------------------------------------------ |
| // html|html4|cp 0% 1.01% 27.73% |
| // urls 0% 0.88% 14.79% |
| // jpg 0% 64.29% 7.14% |
| // pdf 0% 2.56% 58.06% |
| // txt[1-4] 0% 0.23% 0.97% |
| // pb 0% 0.96% 13.88% |
| // bin 0.01% 22.27% 41.17% |
| // |
| // It is very rare that we don't have enough slop for doing block copies. It |
| // is also rare that we need to expand a pattern. Small patterns are common |
| // for incompressible formats and for those we are plenty fast already. |
| // Lengths are normally not greater than 16 but they vary depending on the |
| // input. In general if we always predict len <= 16 it would be an ok |
| // prediction. |
| // |
| // In order to be fast we want a pattern >= 8 bytes and an unrolled loop |
| // copying 2x 8 bytes at a time. |
| |
| // Handle the uncommon case where pattern is less than 8 bytes. |
| if (SNAPPY_PREDICT_FALSE(pattern_size < 8)) { |
| // Expand pattern to at least 8 bytes. The worse case scenario in terms of |
| // buffer usage is when the pattern is size 3. ^ is the original position |
| // of op. x are irrelevant bytes copied by the last UnalignedCopy64. |
| // |
| // abc |
| // abcabcxxxxx |
| // abcabcabcabcxxxxx |
| // ^ |
| // The last x is 14 bytes after ^. |
| if (SNAPPY_PREDICT_TRUE(op <= buf_limit - 14)) { |
| while (pattern_size < 8) { |
| UnalignedCopy64(src, op); |
| op += pattern_size; |
| pattern_size *= 2; |
| } |
| if (SNAPPY_PREDICT_TRUE(op >= op_limit)) return op_limit; |
| } else { |
| return IncrementalCopySlow(src, op, op_limit); |
| } |
| } |
| assert(pattern_size >= 8); |
| |
| // Copy 2x 8 bytes at a time. Because op - src can be < 16, a single |
| // UnalignedCopy128 might overwrite data in op. UnalignedCopy64 is safe |
| // because expanding the pattern to at least 8 bytes guarantees that |
| // op - src >= 8. |
| while (op <= buf_limit - 16) { |
| UnalignedCopy64(src, op); |
| UnalignedCopy64(src + 8, op + 8); |
| src += 16; |
| op += 16; |
| if (SNAPPY_PREDICT_TRUE(op >= op_limit)) return op_limit; |
| } |
| // We only take this branch if we didn't have enough slop and we can do a |
| // single 8 byte copy. |
| if (SNAPPY_PREDICT_FALSE(op <= buf_limit - 8)) { |
| UnalignedCopy64(src, op); |
| src += 8; |
| op += 8; |
| } |
| return IncrementalCopySlow(src, op, op_limit); |
| } |
| |
| } // namespace |
| |
| static inline char* EmitLiteral(char* op, |
| const char* literal, |
| int len, |
| bool allow_fast_path) { |
| // The vast majority of copies are below 16 bytes, for which a |
| // call to memcpy is overkill. This fast path can sometimes |
| // copy up to 15 bytes too much, but that is okay in the |
| // main loop, since we have a bit to go on for both sides: |
| // |
| // - The input will always have kInputMarginBytes = 15 extra |
| // available bytes, as long as we're in the main loop, and |
| // if not, allow_fast_path = false. |
| // - The output will always have 32 spare bytes (see |
| // MaxCompressedLength). |
| assert(len > 0); // Zero-length literals are disallowed |
| int n = len - 1; |
| if (allow_fast_path && len <= 16) { |
| // Fits in tag byte |
| *op++ = LITERAL | (n << 2); |
| |
| UnalignedCopy128(literal, op); |
| return op + len; |
| } |
| |
| if (n < 60) { |
| // Fits in tag byte |
| *op++ = LITERAL | (n << 2); |
| } else { |
| // Encode in upcoming bytes |
| char* base = op; |
| int count = 0; |
| op++; |
| while (n > 0) { |
| *op++ = n & 0xff; |
| n >>= 8; |
| count++; |
| } |
| assert(count >= 1); |
| assert(count <= 4); |
| *base = LITERAL | ((59+count) << 2); |
| } |
| memcpy(op, literal, len); |
| return op + len; |
| } |
| |
| static inline char* EmitCopyAtMost64(char* op, size_t offset, size_t len, |
| bool len_less_than_12) { |
| assert(len <= 64); |
| assert(len >= 4); |
| assert(offset < 65536); |
| assert(len_less_than_12 == (len < 12)); |
| |
| if (len_less_than_12 && SNAPPY_PREDICT_TRUE(offset < 2048)) { |
| // offset fits in 11 bits. The 3 highest go in the top of the first byte, |
| // and the rest go in the second byte. |
| *op++ = COPY_1_BYTE_OFFSET + ((len - 4) << 2) + ((offset >> 3) & 0xe0); |
| *op++ = offset & 0xff; |
| } else { |
| // Write 4 bytes, though we only care about 3 of them. The output buffer |
| // is required to have some slack, so the extra byte won't overrun it. |
| uint32 u = COPY_2_BYTE_OFFSET + ((len - 1) << 2) + (offset << 8); |
| LittleEndian::Store32(op, u); |
| op += 3; |
| } |
| return op; |
| } |
| |
| static inline char* EmitCopy(char* op, size_t offset, size_t len, |
| bool len_less_than_12) { |
| assert(len_less_than_12 == (len < 12)); |
| if (len_less_than_12) { |
| return EmitCopyAtMost64(op, offset, len, true); |
| } else { |
| // A special case for len <= 64 might help, but so far measurements suggest |
| // it's in the noise. |
| |
| // Emit 64 byte copies but make sure to keep at least four bytes reserved. |
| while (SNAPPY_PREDICT_FALSE(len >= 68)) { |
| op = EmitCopyAtMost64(op, offset, 64, false); |
| len -= 64; |
| } |
| |
| // One or two copies will now finish the job. |
| if (len > 64) { |
| op = EmitCopyAtMost64(op, offset, 60, false); |
| len -= 60; |
| } |
| |
| // Emit remainder. |
| op = EmitCopyAtMost64(op, offset, len, len < 12); |
| return op; |
| } |
| } |
| |
| bool GetUncompressedLength(const char* start, size_t n, size_t* result) { |
| uint32 v = 0; |
| const char* limit = start + n; |
| if (Varint::Parse32WithLimit(start, limit, &v) != NULL) { |
| *result = v; |
| return true; |
| } else { |
| return false; |
| } |
| } |
| |
| namespace internal { |
| uint16* WorkingMemory::GetHashTable(size_t input_size, int* table_size) { |
| // Use smaller hash table when input.size() is smaller, since we |
| // fill the table, incurring O(hash table size) overhead for |
| // compression, and if the input is short, we won't need that |
| // many hash table entries anyway. |
| assert(kMaxHashTableSize >= 256); |
| size_t htsize = 256; |
| while (htsize < kMaxHashTableSize && htsize < input_size) { |
| htsize <<= 1; |
| } |
| |
| uint16* table; |
| if (htsize <= ARRAYSIZE(small_table_)) { |
| table = small_table_; |
| } else { |
| if (large_table_ == NULL) { |
| large_table_ = new uint16[kMaxHashTableSize]; |
| } |
| table = large_table_; |
| } |
| |
| *table_size = htsize; |
| memset(table, 0, htsize * sizeof(*table)); |
| return table; |
| } |
| } // end namespace internal |
| |
| // For 0 <= offset <= 4, GetUint32AtOffset(GetEightBytesAt(p), offset) will |
| // equal UNALIGNED_LOAD32(p + offset). Motivation: On x86-64 hardware we have |
| // empirically found that overlapping loads such as |
| // UNALIGNED_LOAD32(p) ... UNALIGNED_LOAD32(p+1) ... UNALIGNED_LOAD32(p+2) |
| // are slower than UNALIGNED_LOAD64(p) followed by shifts and casts to uint32. |
| // |
| // We have different versions for 64- and 32-bit; ideally we would avoid the |
| // two functions and just inline the UNALIGNED_LOAD64 call into |
| // GetUint32AtOffset, but GCC (at least not as of 4.6) is seemingly not clever |
| // enough to avoid loading the value multiple times then. For 64-bit, the load |
| // is done when GetEightBytesAt() is called, whereas for 32-bit, the load is |
| // done at GetUint32AtOffset() time. |
| |
| #ifdef ARCH_K8 |
| |
| typedef uint64 EightBytesReference; |
| |
| static inline EightBytesReference GetEightBytesAt(const char* ptr) { |
| return UNALIGNED_LOAD64(ptr); |
| } |
| |
| static inline uint32 GetUint32AtOffset(uint64 v, int offset) { |
| assert(offset >= 0); |
| assert(offset <= 4); |
| return v >> (LittleEndian::IsLittleEndian() ? 8 * offset : 32 - 8 * offset); |
| } |
| |
| #else |
| |
| typedef const char* EightBytesReference; |
| |
| static inline EightBytesReference GetEightBytesAt(const char* ptr) { |
| return ptr; |
| } |
| |
| static inline uint32 GetUint32AtOffset(const char* v, int offset) { |
| assert(offset >= 0); |
| assert(offset <= 4); |
| return UNALIGNED_LOAD32(v + offset); |
| } |
| |
| #endif |
| |
| // Flat array compression that does not emit the "uncompressed length" |
| // prefix. Compresses "input" string to the "*op" buffer. |
| // |
| // REQUIRES: "input" is at most "kBlockSize" bytes long. |
| // REQUIRES: "op" points to an array of memory that is at least |
| // "MaxCompressedLength(input.size())" in size. |
| // REQUIRES: All elements in "table[0..table_size-1]" are initialized to zero. |
| // REQUIRES: "table_size" is a power of two |
| // |
| // Returns an "end" pointer into "op" buffer. |
| // "end - op" is the compressed size of "input". |
| namespace internal { |
| char* CompressFragment(const char* input, |
| size_t input_size, |
| char* op, |
| uint16* table, |
| const int table_size) { |
| // "ip" is the input pointer, and "op" is the output pointer. |
| const char* ip = input; |
| assert(input_size <= kBlockSize); |
| assert((table_size & (table_size - 1)) == 0); // table must be power of two |
| const int shift = 32 - Bits::Log2Floor(table_size); |
| assert(static_cast<int>(kuint32max >> shift) == table_size - 1); |
| const char* ip_end = input + input_size; |
| const char* base_ip = ip; |
| // Bytes in [next_emit, ip) will be emitted as literal bytes. Or |
| // [next_emit, ip_end) after the main loop. |
| const char* next_emit = ip; |
| |
| const size_t kInputMarginBytes = 15; |
| if (SNAPPY_PREDICT_TRUE(input_size >= kInputMarginBytes)) { |
| const char* ip_limit = input + input_size - kInputMarginBytes; |
| |
| for (uint32 next_hash = Hash(++ip, shift); ; ) { |
| assert(next_emit < ip); |
| // The body of this loop calls EmitLiteral once and then EmitCopy one or |
| // more times. (The exception is that when we're close to exhausting |
| // the input we goto emit_remainder.) |
| // |
| // In the first iteration of this loop we're just starting, so |
| // there's nothing to copy, so calling EmitLiteral once is |
| // necessary. And we only start a new iteration when the |
| // current iteration has determined that a call to EmitLiteral will |
| // precede the next call to EmitCopy (if any). |
| // |
| // Step 1: Scan forward in the input looking for a 4-byte-long match. |
| // If we get close to exhausting the input then goto emit_remainder. |
| // |
| // Heuristic match skipping: If 32 bytes are scanned with no matches |
| // found, start looking only at every other byte. If 32 more bytes are |
| // scanned (or skipped), look at every third byte, etc.. When a match is |
| // found, immediately go back to looking at every byte. This is a small |
| // loss (~5% performance, ~0.1% density) for compressible data due to more |
| // bookkeeping, but for non-compressible data (such as JPEG) it's a huge |
| // win since the compressor quickly "realizes" the data is incompressible |
| // and doesn't bother looking for matches everywhere. |
| // |
| // The "skip" variable keeps track of how many bytes there are since the |
| // last match; dividing it by 32 (ie. right-shifting by five) gives the |
| // number of bytes to move ahead for each iteration. |
| uint32 skip = 32; |
| |
| const char* next_ip = ip; |
| const char* candidate; |
| do { |
| ip = next_ip; |
| uint32 hash = next_hash; |
| assert(hash == Hash(ip, shift)); |
| uint32 bytes_between_hash_lookups = skip >> 5; |
| skip += bytes_between_hash_lookups; |
| next_ip = ip + bytes_between_hash_lookups; |
| if (SNAPPY_PREDICT_FALSE(next_ip > ip_limit)) { |
| goto emit_remainder; |
| } |
| next_hash = Hash(next_ip, shift); |
| candidate = base_ip + table[hash]; |
| assert(candidate >= base_ip); |
| assert(candidate < ip); |
| |
| table[hash] = ip - base_ip; |
| } while (SNAPPY_PREDICT_TRUE(UNALIGNED_LOAD32(ip) != |
| UNALIGNED_LOAD32(candidate))); |
| |
| // Step 2: A 4-byte match has been found. We'll later see if more |
| // than 4 bytes match. But, prior to the match, input |
| // bytes [next_emit, ip) are unmatched. Emit them as "literal bytes." |
| assert(next_emit + 16 <= ip_end); |
| op = EmitLiteral(op, next_emit, ip - next_emit, true); |
| |
| // Step 3: Call EmitCopy, and then see if another EmitCopy could |
| // be our next move. Repeat until we find no match for the |
| // input immediately after what was consumed by the last EmitCopy call. |
| // |
| // If we exit this loop normally then we need to call EmitLiteral next, |
| // though we don't yet know how big the literal will be. We handle that |
| // by proceeding to the next iteration of the main loop. We also can exit |
| // this loop via goto if we get close to exhausting the input. |
| EightBytesReference input_bytes; |
| uint32 candidate_bytes = 0; |
| |
| do { |
| // We have a 4-byte match at ip, and no need to emit any |
| // "literal bytes" prior to ip. |
| const char* base = ip; |
| std::pair<size_t, bool> p = |
| FindMatchLength(candidate + 4, ip + 4, ip_end); |
| size_t matched = 4 + p.first; |
| ip += matched; |
| size_t offset = base - candidate; |
| assert(0 == memcmp(base, candidate, matched)); |
| op = EmitCopy(op, offset, matched, p.second); |
| next_emit = ip; |
| if (SNAPPY_PREDICT_FALSE(ip >= ip_limit)) { |
| goto emit_remainder; |
| } |
| // We are now looking for a 4-byte match again. We read |
| // table[Hash(ip, shift)] for that. To improve compression, |
| // we also update table[Hash(ip - 1, shift)] and table[Hash(ip, shift)]. |
| input_bytes = GetEightBytesAt(ip - 1); |
| uint32 prev_hash = HashBytes(GetUint32AtOffset(input_bytes, 0), shift); |
| table[prev_hash] = ip - base_ip - 1; |
| uint32 cur_hash = HashBytes(GetUint32AtOffset(input_bytes, 1), shift); |
| candidate = base_ip + table[cur_hash]; |
| candidate_bytes = UNALIGNED_LOAD32(candidate); |
| table[cur_hash] = ip - base_ip; |
| } while (GetUint32AtOffset(input_bytes, 1) == candidate_bytes); |
| |
| next_hash = HashBytes(GetUint32AtOffset(input_bytes, 2), shift); |
| ++ip; |
| } |
| } |
| |
| emit_remainder: |
| // Emit the remaining bytes as a literal |
| if (next_emit < ip_end) { |
| op = EmitLiteral(op, next_emit, ip_end - next_emit, false); |
| } |
| |
| return op; |
| } |
| } // end namespace internal |
| |
| // Called back at avery compression call to trace parameters and sizes. |
| static inline void Report(const char *algorithm, size_t compressed_size, |
| size_t uncompressed_size) {} |
| |
| // Signature of output types needed by decompression code. |
| // The decompression code is templatized on a type that obeys this |
| // signature so that we do not pay virtual function call overhead in |
| // the middle of a tight decompression loop. |
| // |
| // class DecompressionWriter { |
| // public: |
| // // Called before decompression |
| // void SetExpectedLength(size_t length); |
| // |
| // // Called after decompression |
| // bool CheckLength() const; |
| // |
| // // Called repeatedly during decompression |
| // bool Append(const char* ip, size_t length); |
| // bool AppendFromSelf(uint32 offset, size_t length); |
| // |
| // // The rules for how TryFastAppend differs from Append are somewhat |
| // // convoluted: |
| // // |
| // // - TryFastAppend is allowed to decline (return false) at any |
| // // time, for any reason -- just "return false" would be |
| // // a perfectly legal implementation of TryFastAppend. |
| // // The intention is for TryFastAppend to allow a fast path |
| // // in the common case of a small append. |
| // // - TryFastAppend is allowed to read up to <available> bytes |
| // // from the input buffer, whereas Append is allowed to read |
| // // <length>. However, if it returns true, it must leave |
| // // at least five (kMaximumTagLength) bytes in the input buffer |
| // // afterwards, so that there is always enough space to read the |
| // // next tag without checking for a refill. |
| // // - TryFastAppend must always return decline (return false) |
| // // if <length> is 61 or more, as in this case the literal length is not |
| // // decoded fully. In practice, this should not be a big problem, |
| // // as it is unlikely that one would implement a fast path accepting |
| // // this much data. |
| // // |
| // bool TryFastAppend(const char* ip, size_t available, size_t length); |
| // }; |
| |
| namespace internal { |
| |
| // Mapping from i in range [0,4] to a mask to extract the bottom 8*i bits |
| static const uint32 wordmask[] = { |
| 0u, 0xffu, 0xffffu, 0xffffffu, 0xffffffffu |
| }; |
| |
| } // end namespace internal |
| |
| // Helper class for decompression |
| class SnappyDecompressor { |
| private: |
| Source* reader_; // Underlying source of bytes to decompress |
| const char* ip_; // Points to next buffered byte |
| const char* ip_limit_; // Points just past buffered bytes |
| uint32 peeked_; // Bytes peeked from reader (need to skip) |
| bool eof_; // Hit end of input without an error? |
| char scratch_[kMaximumTagLength]; // See RefillTag(). |
| |
| // Ensure that all of the tag metadata for the next tag is available |
| // in [ip_..ip_limit_-1]. Also ensures that [ip,ip+4] is readable even |
| // if (ip_limit_ - ip_ < 5). |
| // |
| // Returns true on success, false on error or end of input. |
| bool RefillTag(); |
| |
| public: |
| explicit SnappyDecompressor(Source* reader) |
| : reader_(reader), |
| ip_(NULL), |
| ip_limit_(NULL), |
| peeked_(0), |
| eof_(false) { |
| } |
| |
| ~SnappyDecompressor() { |
| // Advance past any bytes we peeked at from the reader |
| reader_->Skip(peeked_); |
| } |
| |
| // Returns true iff we have hit the end of the input without an error. |
| bool eof() const { |
| return eof_; |
| } |
| |
| // Read the uncompressed length stored at the start of the compressed data. |
| // On succcess, stores the length in *result and returns true. |
| // On failure, returns false. |
| bool ReadUncompressedLength(uint32* result) { |
| assert(ip_ == NULL); // Must not have read anything yet |
| // Length is encoded in 1..5 bytes |
| *result = 0; |
| uint32 shift = 0; |
| while (true) { |
| if (shift >= 32) return false; |
| size_t n; |
| const char* ip = reader_->Peek(&n); |
| if (n == 0) return false; |
| const unsigned char c = *(reinterpret_cast<const unsigned char*>(ip)); |
| reader_->Skip(1); |
| uint32 val = c & 0x7f; |
| if (((val << shift) >> shift) != val) return false; |
| *result |= val << shift; |
| if (c < 128) { |
| break; |
| } |
| shift += 7; |
| } |
| return true; |
| } |
| |
| // Process the next item found in the input. |
| // Returns true if successful, false on error or end of input. |
| template <class Writer> |
| void DecompressAllTags(Writer* writer) { |
| const char* ip = ip_; |
| // For position-independent executables, accessing global arrays can be |
| // slow. Move wordmask array onto the stack to mitigate this. |
| uint32 wordmask[sizeof(internal::wordmask)/sizeof(uint32)]; |
| // Do not use memcpy to copy internal::wordmask to |
| // wordmask. LLVM converts stack arrays to global arrays if it detects |
| // const stack arrays and this hurts the performance of position |
| // independent code. This change is temporary and can be reverted when |
| // https://reviews.llvm.org/D30759 is approved. |
| wordmask[0] = internal::wordmask[0]; |
| wordmask[1] = internal::wordmask[1]; |
| wordmask[2] = internal::wordmask[2]; |
| wordmask[3] = internal::wordmask[3]; |
| wordmask[4] = internal::wordmask[4]; |
| |
| // We could have put this refill fragment only at the beginning of the loop. |
| // However, duplicating it at the end of each branch gives the compiler more |
| // scope to optimize the <ip_limit_ - ip> expression based on the local |
| // context, which overall increases speed. |
| #define MAYBE_REFILL() \ |
| if (ip_limit_ - ip < kMaximumTagLength) { \ |
| ip_ = ip; \ |
| if (!RefillTag()) return; \ |
| ip = ip_; \ |
| } |
| |
| MAYBE_REFILL(); |
| // Add loop alignment directive. Without this directive, we observed |
| // significant performance degradation on several intel architectures |
| // in snappy benchmark built with LLVM. The degradation was caused by |
| // increased branch miss prediction. |
| #if defined(__clang__) && defined(__x86_64__) |
| asm volatile (".p2align 5"); |
| #endif |
| for ( ;; ) { |
| const unsigned char c = *(reinterpret_cast<const unsigned char*>(ip++)); |
| |
| // Ratio of iterations that have LITERAL vs non-LITERAL for different |
| // inputs. |
| // |
| // input LITERAL NON_LITERAL |
| // ----------------------------------- |
| // html|html4|cp 23% 77% |
| // urls 36% 64% |
| // jpg 47% 53% |
| // pdf 19% 81% |
| // txt[1-4] 25% 75% |
| // pb 24% 76% |
| // bin 24% 76% |
| if (SNAPPY_PREDICT_FALSE((c & 0x3) == LITERAL)) { |
| size_t literal_length = (c >> 2) + 1u; |
| if (writer->TryFastAppend(ip, ip_limit_ - ip, literal_length)) { |
| assert(literal_length < 61); |
| ip += literal_length; |
| // NOTE(user): There is no MAYBE_REFILL() here, as TryFastAppend() |
| // will not return true unless there's already at least five spare |
| // bytes in addition to the literal. |
| continue; |
| } |
| if (SNAPPY_PREDICT_FALSE(literal_length >= 61)) { |
| // Long literal. |
| const size_t literal_length_length = literal_length - 60; |
| literal_length = |
| (LittleEndian::Load32(ip) & wordmask[literal_length_length]) + 1; |
| ip += literal_length_length; |
| } |
| |
| size_t avail = ip_limit_ - ip; |
| while (avail < literal_length) { |
| if (!writer->Append(ip, avail)) return; |
| literal_length -= avail; |
| reader_->Skip(peeked_); |
| size_t n; |
| ip = reader_->Peek(&n); |
| avail = n; |
| peeked_ = avail; |
| if (avail == 0) return; // Premature end of input |
| ip_limit_ = ip + avail; |
| } |
| if (!writer->Append(ip, literal_length)) { |
| return; |
| } |
| ip += literal_length; |
| MAYBE_REFILL(); |
| } else { |
| const size_t entry = char_table[c]; |
| const size_t trailer = LittleEndian::Load32(ip) & wordmask[entry >> 11]; |
| const size_t length = entry & 0xff; |
| ip += entry >> 11; |
| |
| // copy_offset/256 is encoded in bits 8..10. By just fetching |
| // those bits, we get copy_offset (since the bit-field starts at |
| // bit 8). |
| const size_t copy_offset = entry & 0x700; |
| if (!writer->AppendFromSelf(copy_offset + trailer, length)) { |
| return; |
| } |
| MAYBE_REFILL(); |
| } |
| } |
| |
| #undef MAYBE_REFILL |
| } |
| }; |
| |
| bool SnappyDecompressor::RefillTag() { |
| const char* ip = ip_; |
| if (ip == ip_limit_) { |
| // Fetch a new fragment from the reader |
| reader_->Skip(peeked_); // All peeked bytes are used up |
| size_t n; |
| ip = reader_->Peek(&n); |
| peeked_ = n; |
| eof_ = (n == 0); |
| if (eof_) return false; |
| ip_limit_ = ip + n; |
| } |
| |
| // Read the tag character |
| assert(ip < ip_limit_); |
| const unsigned char c = *(reinterpret_cast<const unsigned char*>(ip)); |
| const uint32 entry = char_table[c]; |
| const uint32 needed = (entry >> 11) + 1; // +1 byte for 'c' |
| assert(needed <= sizeof(scratch_)); |
| |
| // Read more bytes from reader if needed |
| uint32 nbuf = ip_limit_ - ip; |
| if (nbuf < needed) { |
| // Stitch together bytes from ip and reader to form the word |
| // contents. We store the needed bytes in "scratch_". They |
| // will be consumed immediately by the caller since we do not |
| // read more than we need. |
| memmove(scratch_, ip, nbuf); |
| reader_->Skip(peeked_); // All peeked bytes are used up |
| peeked_ = 0; |
| while (nbuf < needed) { |
| size_t length; |
| const char* src = reader_->Peek(&length); |
| if (length == 0) return false; |
| uint32 to_add = std::min<uint32>(needed - nbuf, length); |
| memcpy(scratch_ + nbuf, src, to_add); |
| nbuf += to_add; |
| reader_->Skip(to_add); |
| } |
| assert(nbuf == needed); |
| ip_ = scratch_; |
| ip_limit_ = scratch_ + needed; |
| } else if (nbuf < kMaximumTagLength) { |
| // Have enough bytes, but move into scratch_ so that we do not |
| // read past end of input |
| memmove(scratch_, ip, nbuf); |
| reader_->Skip(peeked_); // All peeked bytes are used up |
| peeked_ = 0; |
| ip_ = scratch_; |
| ip_limit_ = scratch_ + nbuf; |
| } else { |
| // Pass pointer to buffer returned by reader_. |
| ip_ = ip; |
| } |
| return true; |
| } |
| |
| template <typename Writer> |
| static bool InternalUncompress(Source* r, Writer* writer) { |
| // Read the uncompressed length from the front of the compressed input |
| SnappyDecompressor decompressor(r); |
| uint32 uncompressed_len = 0; |
| if (!decompressor.ReadUncompressedLength(&uncompressed_len)) return false; |
| |
| return InternalUncompressAllTags(&decompressor, writer, r->Available(), |
| uncompressed_len); |
| } |
| |
| template <typename Writer> |
| static bool InternalUncompressAllTags(SnappyDecompressor* decompressor, |
| Writer* writer, |
| uint32 compressed_len, |
| uint32 uncompressed_len) { |
| Report("snappy_uncompress", compressed_len, uncompressed_len); |
| |
| writer->SetExpectedLength(uncompressed_len); |
| |
| // Process the entire input |
| decompressor->DecompressAllTags(writer); |
| writer->Flush(); |
| return (decompressor->eof() && writer->CheckLength()); |
| } |
| |
| bool GetUncompressedLength(Source* source, uint32* result) { |
| SnappyDecompressor decompressor(source); |
| return decompressor.ReadUncompressedLength(result); |
| } |
| |
| size_t Compress(Source* reader, Sink* writer) { |
| size_t written = 0; |
| size_t N = reader->Available(); |
| const size_t uncompressed_size = N; |
| char ulength[Varint::kMax32]; |
| char* p = Varint::Encode32(ulength, N); |
| writer->Append(ulength, p-ulength); |
| written += (p - ulength); |
| |
| internal::WorkingMemory wmem; |
| char* scratch = NULL; |
| char* scratch_output = NULL; |
| |
| while (N > 0) { |
| // Get next block to compress (without copying if possible) |
| size_t fragment_size; |
| const char* fragment = reader->Peek(&fragment_size); |
| assert(fragment_size != 0); // premature end of input |
| const size_t num_to_read = std::min(N, kBlockSize); |
| size_t bytes_read = fragment_size; |
| |
| size_t pending_advance = 0; |
| if (bytes_read >= num_to_read) { |
| // Buffer returned by reader is large enough |
| pending_advance = num_to_read; |
| fragment_size = num_to_read; |
| } else { |
| // Read into scratch buffer |
| if (scratch == NULL) { |
| // If this is the last iteration, we want to allocate N bytes |
| // of space, otherwise the max possible kBlockSize space. |
| // num_to_read contains exactly the correct value |
| scratch = new char[num_to_read]; |
| } |
| memcpy(scratch, fragment, bytes_read); |
| reader->Skip(bytes_read); |
| |
| while (bytes_read < num_to_read) { |
| fragment = reader->Peek(&fragment_size); |
| size_t n = std::min<size_t>(fragment_size, num_to_read - bytes_read); |
| memcpy(scratch + bytes_read, fragment, n); |
| bytes_read += n; |
| reader->Skip(n); |
| } |
| assert(bytes_read == num_to_read); |
| fragment = scratch; |
| fragment_size = num_to_read; |
| } |
| assert(fragment_size == num_to_read); |
| |
| // Get encoding table for compression |
| int table_size; |
| uint16* table = wmem.GetHashTable(num_to_read, &table_size); |
| |
| // Compress input_fragment and append to dest |
| const int max_output = MaxCompressedLength(num_to_read); |
| |
| // Need a scratch buffer for the output, in case the byte sink doesn't |
| // have room for us directly. |
| if (scratch_output == NULL) { |
| scratch_output = new char[max_output]; |
| } else { |
| // Since we encode kBlockSize regions followed by a region |
| // which is <= kBlockSize in length, a previously allocated |
| // scratch_output[] region is big enough for this iteration. |
| } |
| char* dest = writer->GetAppendBuffer(max_output, scratch_output); |
| char* end = internal::CompressFragment(fragment, fragment_size, |
| dest, table, table_size); |
| writer->Append(dest, end - dest); |
| written += (end - dest); |
| |
| N -= num_to_read; |
| reader->Skip(pending_advance); |
| } |
| |
| Report("snappy_compress", written, uncompressed_size); |
| |
| delete[] scratch; |
| delete[] scratch_output; |
| |
| return written; |
| } |
| |
| // ----------------------------------------------------------------------- |
| // IOVec interfaces |
| // ----------------------------------------------------------------------- |
| |
| // A type that writes to an iovec. |
| // Note that this is not a "ByteSink", but a type that matches the |
| // Writer template argument to SnappyDecompressor::DecompressAllTags(). |
| class SnappyIOVecWriter { |
| private: |
| const struct iovec* output_iov_; |
| const size_t output_iov_count_; |
| |
| // We are currently writing into output_iov_[curr_iov_index_]. |
| size_t curr_iov_index_; |
| |
| // Bytes written to output_iov_[curr_iov_index_] so far. |
| size_t curr_iov_written_; |
| |
| // Total bytes decompressed into output_iov_ so far. |
| size_t total_written_; |
| |
| // Maximum number of bytes that will be decompressed into output_iov_. |
| size_t output_limit_; |
| |
| inline char* GetIOVecPointer(size_t index, size_t offset) { |
| return reinterpret_cast<char*>(output_iov_[index].iov_base) + |
| offset; |
| } |
| |
| public: |
| // Does not take ownership of iov. iov must be valid during the |
| // entire lifetime of the SnappyIOVecWriter. |
| inline SnappyIOVecWriter(const struct iovec* iov, size_t iov_count) |
| : output_iov_(iov), |
| output_iov_count_(iov_count), |
| curr_iov_index_(0), |
| curr_iov_written_(0), |
| total_written_(0), |
| output_limit_(-1) { |
| } |
| |
| inline void SetExpectedLength(size_t len) { |
| output_limit_ = len; |
| } |
| |
| inline bool CheckLength() const { |
| return total_written_ == output_limit_; |
| } |
| |
| inline bool Append(const char* ip, size_t len) { |
| if (total_written_ + len > output_limit_) { |
| return false; |
| } |
| |
| while (len > 0) { |
| assert(curr_iov_written_ <= output_iov_[curr_iov_index_].iov_len); |
| if (curr_iov_written_ >= output_iov_[curr_iov_index_].iov_len) { |
| // This iovec is full. Go to the next one. |
| if (curr_iov_index_ + 1 >= output_iov_count_) { |
| return false; |
| } |
| curr_iov_written_ = 0; |
| ++curr_iov_index_; |
| } |
| |
| const size_t to_write = std::min( |
| len, output_iov_[curr_iov_index_].iov_len - curr_iov_written_); |
| memcpy(GetIOVecPointer(curr_iov_index_, curr_iov_written_), |
| ip, |
| to_write); |
| curr_iov_written_ += to_write; |
| total_written_ += to_write; |
| ip += to_write; |
| len -= to_write; |
| } |
| |
| return true; |
| } |
| |
| inline bool TryFastAppend(const char* ip, size_t available, size_t len) { |
| const size_t space_left = output_limit_ - total_written_; |
| if (len <= 16 && available >= 16 + kMaximumTagLength && space_left >= 16 && |
| output_iov_[curr_iov_index_].iov_len - curr_iov_written_ >= 16) { |
| // Fast path, used for the majority (about 95%) of invocations. |
| char* ptr = GetIOVecPointer(curr_iov_index_, curr_iov_written_); |
| UnalignedCopy128(ip, ptr); |
| curr_iov_written_ += len; |
| total_written_ += len; |
| return true; |
| } |
| |
| return false; |
| } |
| |
| inline bool AppendFromSelf(size_t offset, size_t len) { |
| if (offset > total_written_ || offset == 0) { |
| return false; |
| } |
| const size_t space_left = output_limit_ - total_written_; |
| if (len > space_left) { |
| return false; |
| } |
| |
| // Locate the iovec from which we need to start the copy. |
| size_t from_iov_index = curr_iov_index_; |
| size_t from_iov_offset = curr_iov_written_; |
| while (offset > 0) { |
| if (from_iov_offset >= offset) { |
| from_iov_offset -= offset; |
| break; |
| } |
| |
| offset -= from_iov_offset; |
| assert(from_iov_index > 0); |
| --from_iov_index; |
| from_iov_offset = output_iov_[from_iov_index].iov_len; |
| } |
| |
| // Copy <len> bytes starting from the iovec pointed to by from_iov_index to |
| // the current iovec. |
| while (len > 0) { |
| assert(from_iov_index <= curr_iov_index_); |
| if (from_iov_index != curr_iov_index_) { |
| const size_t to_copy = std::min( |
| output_iov_[from_iov_index].iov_len - from_iov_offset, |
| len); |
| Append(GetIOVecPointer(from_iov_index, from_iov_offset), to_copy); |
| len -= to_copy; |
| if (len > 0) { |
| ++from_iov_index; |
| from_iov_offset = 0; |
| } |
| } else { |
| assert(curr_iov_written_ <= output_iov_[curr_iov_index_].iov_len); |
| size_t to_copy = std::min(output_iov_[curr_iov_index_].iov_len - |
| curr_iov_written_, |
| len); |
| if (to_copy == 0) { |
| // This iovec is full. Go to the next one. |
| if (curr_iov_index_ + 1 >= output_iov_count_) { |
| return false; |
| } |
| ++curr_iov_index_; |
| curr_iov_written_ = 0; |
| continue; |
| } |
| if (to_copy > len) { |
| to_copy = len; |
| } |
| IncrementalCopySlow( |
| GetIOVecPointer(from_iov_index, from_iov_offset), |
| GetIOVecPointer(curr_iov_index_, curr_iov_written_), |
| GetIOVecPointer(curr_iov_index_, curr_iov_written_) + to_copy); |
| curr_iov_written_ += to_copy; |
| from_iov_offset += to_copy; |
| total_written_ += to_copy; |
| len -= to_copy; |
| } |
| } |
| |
| return true; |
| } |
| |
| inline void Flush() {} |
| }; |
| |
| bool RawUncompressToIOVec(const char* compressed, size_t compressed_length, |
| const struct iovec* iov, size_t iov_cnt) { |
| ByteArraySource reader(compressed, compressed_length); |
| return RawUncompressToIOVec(&reader, iov, iov_cnt); |
| } |
| |
| bool RawUncompressToIOVec(Source* compressed, const struct iovec* iov, |
| size_t iov_cnt) { |
| SnappyIOVecWriter output(iov, iov_cnt); |
| return InternalUncompress(compressed, &output); |
| } |
| |
| // ----------------------------------------------------------------------- |
| // Flat array interfaces |
| // ----------------------------------------------------------------------- |
| |
| // A type that writes to a flat array. |
| // Note that this is not a "ByteSink", but a type that matches the |
| // Writer template argument to SnappyDecompressor::DecompressAllTags(). |
| class SnappyArrayWriter { |
| private: |
| char* base_; |
| char* op_; |
| char* op_limit_; |
| |
| public: |
| inline explicit SnappyArrayWriter(char* dst) |
| : base_(dst), |
| op_(dst), |
| op_limit_(dst) { |
| } |
| |
| inline void SetExpectedLength(size_t len) { |
| op_limit_ = op_ + len; |
| } |
| |
| inline bool CheckLength() const { |
| return op_ == op_limit_; |
| } |
| |
| inline bool Append(const char* ip, size_t len) { |
| char* op = op_; |
| const size_t space_left = op_limit_ - op; |
| if (space_left < len) { |
| return false; |
| } |
| memcpy(op, ip, len); |
| op_ = op + len; |
| return true; |
| } |
| |
| inline bool TryFastAppend(const char* ip, size_t available, size_t len) { |
| char* op = op_; |
| const size_t space_left = op_limit_ - op; |
| if (len <= 16 && available >= 16 + kMaximumTagLength && space_left >= 16) { |
| // Fast path, used for the majority (about 95%) of invocations. |
| UnalignedCopy128(ip, op); |
| op_ = op + len; |
| return true; |
| } else { |
| return false; |
| } |
| } |
| |
| inline bool AppendFromSelf(size_t offset, size_t len) { |
| char* const op_end = op_ + len; |
| |
| // Check if we try to append from before the start of the buffer. |
| // Normally this would just be a check for "produced < offset", |
| // but "produced <= offset - 1u" is equivalent for every case |
| // except the one where offset==0, where the right side will wrap around |
| // to a very big number. This is convenient, as offset==0 is another |
| // invalid case that we also want to catch, so that we do not go |
| // into an infinite loop. |
| if (Produced() <= offset - 1u || op_end > op_limit_) return false; |
| op_ = IncrementalCopy(op_ - offset, op_, op_end, op_limit_); |
| |
| return true; |
| } |
| inline size_t Produced() const { |
| assert(op_ >= base_); |
| return op_ - base_; |
| } |
| inline void Flush() {} |
| }; |
| |
| bool RawUncompress(const char* compressed, size_t n, char* uncompressed) { |
| ByteArraySource reader(compressed, n); |
| return RawUncompress(&reader, uncompressed); |
| } |
| |
| bool RawUncompress(Source* compressed, char* uncompressed) { |
| SnappyArrayWriter output(uncompressed); |
| return InternalUncompress(compressed, &output); |
| } |
| |
| bool Uncompress(const char* compressed, size_t n, string* uncompressed) { |
| size_t ulength; |
| if (!GetUncompressedLength(compressed, n, &ulength)) { |
| return false; |
| } |
| // On 32-bit builds: max_size() < kuint32max. Check for that instead |
| // of crashing (e.g., consider externally specified compressed data). |
| if (ulength > uncompressed->max_size()) { |
| return false; |
| } |
| STLStringResizeUninitialized(uncompressed, ulength); |
| return RawUncompress(compressed, n, string_as_array(uncompressed)); |
| } |
| |
| // A Writer that drops everything on the floor and just does validation |
| class SnappyDecompressionValidator { |
| private: |
| size_t expected_; |
| size_t produced_; |
| |
| public: |
| inline SnappyDecompressionValidator() : expected_(0), produced_(0) { } |
| inline void SetExpectedLength(size_t len) { |
| expected_ = len; |
| } |
| inline bool CheckLength() const { |
| return expected_ == produced_; |
| } |
| inline bool Append(const char* ip, size_t len) { |
| produced_ += len; |
| return produced_ <= expected_; |
| } |
| inline bool TryFastAppend(const char* ip, size_t available, size_t length) { |
| return false; |
| } |
| inline bool AppendFromSelf(size_t offset, size_t len) { |
| // See SnappyArrayWriter::AppendFromSelf for an explanation of |
| // the "offset - 1u" trick. |
| if (produced_ <= offset - 1u) return false; |
| produced_ += len; |
| return produced_ <= expected_; |
| } |
| inline void Flush() {} |
| }; |
| |
| bool IsValidCompressedBuffer(const char* compressed, size_t n) { |
| ByteArraySource reader(compressed, n); |
| SnappyDecompressionValidator writer; |
| return InternalUncompress(&reader, &writer); |
| } |
| |
| bool IsValidCompressed(Source* compressed) { |
| SnappyDecompressionValidator writer; |
| return InternalUncompress(compressed, &writer); |
| } |
| |
| void RawCompress(const char* input, |
| size_t input_length, |
| char* compressed, |
| size_t* compressed_length) { |
| ByteArraySource reader(input, input_length); |
| UncheckedByteArraySink writer(compressed); |
| Compress(&reader, &writer); |
| |
| // Compute how many bytes were added |
| *compressed_length = (writer.CurrentDestination() - compressed); |
| } |
| |
| size_t Compress(const char* input, size_t input_length, string* compressed) { |
| // Pre-grow the buffer to the max length of the compressed output |
| STLStringResizeUninitialized(compressed, MaxCompressedLength(input_length)); |
| |
| size_t compressed_length; |
| RawCompress(input, input_length, string_as_array(compressed), |
| &compressed_length); |
| compressed->resize(compressed_length); |
| return compressed_length; |
| } |
| |
| // ----------------------------------------------------------------------- |
| // Sink interface |
| // ----------------------------------------------------------------------- |
| |
| // A type that decompresses into a Sink. The template parameter |
| // Allocator must export one method "char* Allocate(int size);", which |
| // allocates a buffer of "size" and appends that to the destination. |
| template <typename Allocator> |
| class SnappyScatteredWriter { |
| Allocator allocator_; |
| |
| // We need random access into the data generated so far. Therefore |
| // we keep track of all of the generated data as an array of blocks. |
| // All of the blocks except the last have length kBlockSize. |
| std::vector<char*> blocks_; |
| size_t expected_; |
| |
| // Total size of all fully generated blocks so far |
| size_t full_size_; |
| |
| // Pointer into current output block |
| char* op_base_; // Base of output block |
| char* op_ptr_; // Pointer to next unfilled byte in block |
| char* op_limit_; // Pointer just past block |
| |
| inline size_t Size() const { |
| return full_size_ + (op_ptr_ - op_base_); |
| } |
| |
| bool SlowAppend(const char* ip, size_t len); |
| bool SlowAppendFromSelf(size_t offset, size_t len); |
| |
| public: |
| inline explicit SnappyScatteredWriter(const Allocator& allocator) |
| : allocator_(allocator), |
| full_size_(0), |
| op_base_(NULL), |
| op_ptr_(NULL), |
| op_limit_(NULL) { |
| } |
| |
| inline void SetExpectedLength(size_t len) { |
| assert(blocks_.empty()); |
| expected_ = len; |
| } |
| |
| inline bool CheckLength() const { |
| return Size() == expected_; |
| } |
| |
| // Return the number of bytes actually uncompressed so far |
| inline size_t Produced() const { |
| return Size(); |
| } |
| |
| inline bool Append(const char* ip, size_t len) { |
| size_t avail = op_limit_ - op_ptr_; |
| if (len <= avail) { |
| // Fast path |
| memcpy(op_ptr_, ip, len); |
| op_ptr_ += len; |
| return true; |
| } else { |
| return SlowAppend(ip, len); |
| } |
| } |
| |
| inline bool TryFastAppend(const char* ip, size_t available, size_t length) { |
| char* op = op_ptr_; |
| const int space_left = op_limit_ - op; |
| if (length <= 16 && available >= 16 + kMaximumTagLength && |
| space_left >= 16) { |
| // Fast path, used for the majority (about 95%) of invocations. |
| UnalignedCopy128(ip, op); |
| op_ptr_ = op + length; |
| return true; |
| } else { |
| return false; |
| } |
| } |
| |
| inline bool AppendFromSelf(size_t offset, size_t len) { |
| char* const op_end = op_ptr_ + len; |
| // See SnappyArrayWriter::AppendFromSelf for an explanation of |
| // the "offset - 1u" trick. |
| if (SNAPPY_PREDICT_TRUE(offset - 1u < op_ptr_ - op_base_ && |
| op_end <= op_limit_)) { |
| // Fast path: src and dst in current block. |
| op_ptr_ = IncrementalCopy(op_ptr_ - offset, op_ptr_, op_end, op_limit_); |
| return true; |
| } |
| return SlowAppendFromSelf(offset, len); |
| } |
| |
| // Called at the end of the decompress. We ask the allocator |
| // write all blocks to the sink. |
| inline void Flush() { allocator_.Flush(Produced()); } |
| }; |
| |
| template<typename Allocator> |
| bool SnappyScatteredWriter<Allocator>::SlowAppend(const char* ip, size_t len) { |
| size_t avail = op_limit_ - op_ptr_; |
| while (len > avail) { |
| // Completely fill this block |
| memcpy(op_ptr_, ip, avail); |
| op_ptr_ += avail; |
| assert(op_limit_ - op_ptr_ == 0); |
| full_size_ += (op_ptr_ - op_base_); |
| len -= avail; |
| ip += avail; |
| |
| // Bounds check |
| if (full_size_ + len > expected_) { |
| return false; |
| } |
| |
| // Make new block |
| size_t bsize = std::min<size_t>(kBlockSize, expected_ - full_size_); |
| op_base_ = allocator_.Allocate(bsize); |
| op_ptr_ = op_base_; |
| op_limit_ = op_base_ + bsize; |
| blocks_.push_back(op_base_); |
| avail = bsize; |
| } |
| |
| memcpy(op_ptr_, ip, len); |
| op_ptr_ += len; |
| return true; |
| } |
| |
| template<typename Allocator> |
| bool SnappyScatteredWriter<Allocator>::SlowAppendFromSelf(size_t offset, |
| size_t len) { |
| // Overflow check |
| // See SnappyArrayWriter::AppendFromSelf for an explanation of |
| // the "offset - 1u" trick. |
| const size_t cur = Size(); |
| if (offset - 1u >= cur) return false; |
| if (expected_ - cur < len) return false; |
| |
| // Currently we shouldn't ever hit this path because Compress() chops the |
| // input into blocks and does not create cross-block copies. However, it is |
| // nice if we do not rely on that, since we can get better compression if we |
| // allow cross-block copies and thus might want to change the compressor in |
| // the future. |
| size_t src = cur - offset; |
| while (len-- > 0) { |
| char c = blocks_[src >> kBlockLog][src & (kBlockSize-1)]; |
| Append(&c, 1); |
| src++; |
| } |
| return true; |
| } |
| |
| class SnappySinkAllocator { |
| public: |
| explicit SnappySinkAllocator(Sink* dest): dest_(dest) {} |
| ~SnappySinkAllocator() {} |
| |
| char* Allocate(int size) { |
| Datablock block(new char[size], size); |
| blocks_.push_back(block); |
| return block.data; |
| } |
| |
| // We flush only at the end, because the writer wants |
| // random access to the blocks and once we hand the |
| // block over to the sink, we can't access it anymore. |
| // Also we don't write more than has been actually written |
| // to the blocks. |
| void Flush(size_t size) { |
| size_t size_written = 0; |
| size_t block_size; |
| for (int i = 0; i < blocks_.size(); ++i) { |
| block_size = std::min<size_t>(blocks_[i].size, size - size_written); |
| dest_->AppendAndTakeOwnership(blocks_[i].data, block_size, |
| &SnappySinkAllocator::Deleter, NULL); |
| size_written += block_size; |
| } |
| blocks_.clear(); |
| } |
| |
| private: |
| struct Datablock { |
| char* data; |
| size_t size; |
| Datablock(char* p, size_t s) : data(p), size(s) {} |
| }; |
| |
| static void Deleter(void* arg, const char* bytes, size_t size) { |
| delete[] bytes; |
| } |
| |
| Sink* dest_; |
| std::vector<Datablock> blocks_; |
| |
| // Note: copying this object is allowed |
| }; |
| |
| size_t UncompressAsMuchAsPossible(Source* compressed, Sink* uncompressed) { |
| SnappySinkAllocator allocator(uncompressed); |
| SnappyScatteredWriter<SnappySinkAllocator> writer(allocator); |
| InternalUncompress(compressed, &writer); |
| return writer.Produced(); |
| } |
| |
| bool Uncompress(Source* compressed, Sink* uncompressed) { |
| // Read the uncompressed length from the front of the compressed input |
| SnappyDecompressor decompressor(compressed); |
| uint32 uncompressed_len = 0; |
| if (!decompressor.ReadUncompressedLength(&uncompressed_len)) { |
| return false; |
| } |
| |
| char c; |
| size_t allocated_size; |
| char* buf = uncompressed->GetAppendBufferVariable( |
| 1, uncompressed_len, &c, 1, &allocated_size); |
| |
| const size_t compressed_len = compressed->Available(); |
| // If we can get a flat buffer, then use it, otherwise do block by block |
| // uncompression |
| if (allocated_size >= uncompressed_len) { |
| SnappyArrayWriter writer(buf); |
| bool result = InternalUncompressAllTags(&decompressor, &writer, |
| compressed_len, uncompressed_len); |
| uncompressed->Append(buf, writer.Produced()); |
| return result; |
| } else { |
| SnappySinkAllocator allocator(uncompressed); |
| SnappyScatteredWriter<SnappySinkAllocator> writer(allocator); |
| return InternalUncompressAllTags(&decompressor, &writer, compressed_len, |
| uncompressed_len); |
| } |
| } |
| |
| } // end namespace snappy |