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Diffstat (limited to 'snappy/snappy.cc')
| -rw-r--r-- | snappy/snappy.cc | 1119 |
1 files changed, 0 insertions, 1119 deletions
diff --git a/snappy/snappy.cc b/snappy/snappy.cc deleted file mode 100644 index 1230321f..00000000 --- a/snappy/snappy.cc +++ /dev/null @@ -1,1119 +0,0 @@ -// 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" - -#include <stdio.h> - -#include <algorithm> -#include <string> -#include <vector> - - -namespace snappy { - -// 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; -} - -enum { - LITERAL = 0, - COPY_1_BYTE_OFFSET = 1, // 3 bit length + 3 bits of offset in opcode - COPY_2_BYTE_OFFSET = 2, - COPY_4_BYTE_OFFSET = 3 -}; - -// Copy "len" bytes from "src" to "op", one 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 -// len == 20 -// After IncrementalCopy(src, op, len), the result will have -// eleven copies of "ab" -// ababababababababababab -// Note that this does not match the semantics of either memcpy() -// or memmove(). -static inline void IncrementalCopy(const char* src, char* op, int len) { - assert(len > 0); - do { - *op++ = *src++; - } while (--len > 0); -} - -// Equivalent to IncrementalCopy except that it can write up to ten extra -// bytes after the end of the copy, and that it is faster. -// -// The main part of this loop is a simple copy of eight bytes at a time until -// we've copied (at least) the requested amount of bytes. However, if op and -// src are less than eight bytes apart (indicating a repeating pattern of -// length < 8), we first need to expand the pattern in order to get the correct -// results. For instance, if the buffer looks like this, with the eight-byte -// <src> and <op> patterns marked as intervals: -// -// abxxxxxxxxxxxx -// [------] src -// [------] op -// -// a single eight-byte copy from <src> to <op> will repeat the pattern once, -// after which we can move <op> two bytes without moving <src>: -// -// ababxxxxxxxxxx -// [------] src -// [------] op -// -// and repeat the exercise until the two no longer overlap. -// -// This allows us to do very well in the special case of one single byte -// repeated many times, without taking a big hit for more general cases. -// -// The worst case of extra writing past the end of the match occurs when -// op - src == 1 and len == 1; the last copy will read from byte positions -// [0..7] and write to [4..11], whereas it was only supposed to write to -// position 1. Thus, ten excess bytes. - -namespace { - -const int kMaxIncrementCopyOverflow = 10; - -} // namespace - -static inline void IncrementalCopyFastPath(const char* src, char* op, int len) { - while (op - src < 8) { - UnalignedCopy64(src, op); - len -= op - src; - op += op - src; - } - while (len > 0) { - UnalignedCopy64(src, op); - src += 8; - op += 8; - len -= 8; - } -} - -static inline char* EmitLiteral(char* op, - const char* literal, - int len, - bool allow_fast_path) { - int n = len - 1; // Zero-length literals are disallowed - if (n < 60) { - // Fits in tag byte - *op++ = LITERAL | (n << 2); - - // 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). - if (allow_fast_path && len <= 16) { - UnalignedCopy64(literal, op); - UnalignedCopy64(literal + 8, op + 8); - return op + len; - } - } 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* EmitCopyLessThan64(char* op, size_t offset, int len) { - assert(len <= 64); - assert(len >= 4); - assert(offset < 65536); - - if ((len < 12) && (offset < 2048)) { - size_t len_minus_4 = len - 4; - assert(len_minus_4 < 8); // Must fit in 3 bits - *op++ = COPY_1_BYTE_OFFSET + ((len_minus_4) << 2) + ((offset >> 8) << 5); - *op++ = offset & 0xff; - } else { - *op++ = COPY_2_BYTE_OFFSET + ((len-1) << 2); - LittleEndian::Store16(op, offset); - op += 2; - } - return op; -} - -static inline char* EmitCopy(char* op, size_t offset, int len) { - // Emit 64 byte copies but make sure to keep at least four bytes reserved - while (len >= 68) { - op = EmitCopyLessThan64(op, offset, 64); - len -= 64; - } - - // Emit an extra 60 byte copy if have too much data to fit in one copy - if (len > 64) { - op = EmitCopyLessThan64(op, offset, 60); - len -= 60; - } - - // Emit remainder - op = EmitCopyLessThan64(op, offset, len); - 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 (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, 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; - next_ip = ip + bytes_between_hash_lookups; - if (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 (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; - int matched = 4 + FindMatchLength(candidate + 4, ip + 4, ip_end); - ip += matched; - size_t offset = base - candidate; - assert(0 == memcmp(base, candidate, matched)); - op = EmitCopy(op, offset, matched); - // We could immediately start working at ip now, but to improve - // compression we first update table[Hash(ip - 1, ...)]. - const char* insert_tail = ip - 1; - next_emit = ip; - if (PREDICT_FALSE(ip >= ip_limit)) { - goto emit_remainder; - } - input_bytes = GetEightBytesAt(insert_tail); - 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 - -// 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 difference between TryFastAppend and Append is that TryFastAppend -// // is allowed to read up to <available> bytes from the input buffer, -// // whereas Append is allowed to read <length>. -// // -// // Also, TryFastAppend is allowed to return false, declining the append, -// // without it being a fatal error -- 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. -// // -// // NOTE(user): 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); -// }; - -// ----------------------------------------------------------------------- -// Lookup table for decompression code. Generated by ComputeTable() below. -// ----------------------------------------------------------------------- - -// 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 -}; - -// Data stored per entry in lookup table: -// Range Bits-used Description -// ------------------------------------ -// 1..64 0..7 Literal/copy length encoded in opcode byte -// 0..7 8..10 Copy offset encoded in opcode byte / 256 -// 0..4 11..13 Extra bytes after opcode -// -// We use eight bits for the length even though 7 would have sufficed -// because of efficiency reasons: -// (1) Extracting a byte is faster than a bit-field -// (2) It properly aligns copy offset so we do not need a <<8 -static const uint16 char_table[256] = { - 0x0001, 0x0804, 0x1001, 0x2001, 0x0002, 0x0805, 0x1002, 0x2002, - 0x0003, 0x0806, 0x1003, 0x2003, 0x0004, 0x0807, 0x1004, 0x2004, - 0x0005, 0x0808, 0x1005, 0x2005, 0x0006, 0x0809, 0x1006, 0x2006, - 0x0007, 0x080a, 0x1007, 0x2007, 0x0008, 0x080b, 0x1008, 0x2008, - 0x0009, 0x0904, 0x1009, 0x2009, 0x000a, 0x0905, 0x100a, 0x200a, - 0x000b, 0x0906, 0x100b, 0x200b, 0x000c, 0x0907, 0x100c, 0x200c, - 0x000d, 0x0908, 0x100d, 0x200d, 0x000e, 0x0909, 0x100e, 0x200e, - 0x000f, 0x090a, 0x100f, 0x200f, 0x0010, 0x090b, 0x1010, 0x2010, - 0x0011, 0x0a04, 0x1011, 0x2011, 0x0012, 0x0a05, 0x1012, 0x2012, - 0x0013, 0x0a06, 0x1013, 0x2013, 0x0014, 0x0a07, 0x1014, 0x2014, - 0x0015, 0x0a08, 0x1015, 0x2015, 0x0016, 0x0a09, 0x1016, 0x2016, - 0x0017, 0x0a0a, 0x1017, 0x2017, 0x0018, 0x0a0b, 0x1018, 0x2018, - 0x0019, 0x0b04, 0x1019, 0x2019, 0x001a, 0x0b05, 0x101a, 0x201a, - 0x001b, 0x0b06, 0x101b, 0x201b, 0x001c, 0x0b07, 0x101c, 0x201c, - 0x001d, 0x0b08, 0x101d, 0x201d, 0x001e, 0x0b09, 0x101e, 0x201e, - 0x001f, 0x0b0a, 0x101f, 0x201f, 0x0020, 0x0b0b, 0x1020, 0x2020, - 0x0021, 0x0c04, 0x1021, 0x2021, 0x0022, 0x0c05, 0x1022, 0x2022, - 0x0023, 0x0c06, 0x1023, 0x2023, 0x0024, 0x0c07, 0x1024, 0x2024, - 0x0025, 0x0c08, 0x1025, 0x2025, 0x0026, 0x0c09, 0x1026, 0x2026, - 0x0027, 0x0c0a, 0x1027, 0x2027, 0x0028, 0x0c0b, 0x1028, 0x2028, - 0x0029, 0x0d04, 0x1029, 0x2029, 0x002a, 0x0d05, 0x102a, 0x202a, - 0x002b, 0x0d06, 0x102b, 0x202b, 0x002c, 0x0d07, 0x102c, 0x202c, - 0x002d, 0x0d08, 0x102d, 0x202d, 0x002e, 0x0d09, 0x102e, 0x202e, - 0x002f, 0x0d0a, 0x102f, 0x202f, 0x0030, 0x0d0b, 0x1030, 0x2030, - 0x0031, 0x0e04, 0x1031, 0x2031, 0x0032, 0x0e05, 0x1032, 0x2032, - 0x0033, 0x0e06, 0x1033, 0x2033, 0x0034, 0x0e07, 0x1034, 0x2034, - 0x0035, 0x0e08, 0x1035, 0x2035, 0x0036, 0x0e09, 0x1036, 0x2036, - 0x0037, 0x0e0a, 0x1037, 0x2037, 0x0038, 0x0e0b, 0x1038, 0x2038, - 0x0039, 0x0f04, 0x1039, 0x2039, 0x003a, 0x0f05, 0x103a, 0x203a, - 0x003b, 0x0f06, 0x103b, 0x203b, 0x003c, 0x0f07, 0x103c, 0x203c, - 0x0801, 0x0f08, 0x103d, 0x203d, 0x1001, 0x0f09, 0x103e, 0x203e, - 0x1801, 0x0f0a, 0x103f, 0x203f, 0x2001, 0x0f0b, 0x1040, 0x2040 -}; - -// In debug mode, allow optional computation of the table at startup. -// Also, check that the decompression table is correct. -#ifndef NDEBUG -DEFINE_bool(snappy_dump_decompression_table, false, - "If true, we print the decompression table at startup."); - -static uint16 MakeEntry(unsigned int extra, - unsigned int len, - unsigned int copy_offset) { - // Check that all of the fields fit within the allocated space - assert(extra == (extra & 0x7)); // At most 3 bits - assert(copy_offset == (copy_offset & 0x7)); // At most 3 bits - assert(len == (len & 0x7f)); // At most 7 bits - return len | (copy_offset << 8) | (extra << 11); -} - -static void ComputeTable() { - uint16 dst[256]; - - // Place invalid entries in all places to detect missing initialization - int assigned = 0; - for (int i = 0; i < 256; i++) { - dst[i] = 0xffff; - } - - // Small LITERAL entries. We store (len-1) in the top 6 bits. - for (unsigned int len = 1; len <= 60; len++) { - dst[LITERAL | ((len-1) << 2)] = MakeEntry(0, len, 0); - assigned++; - } - - // Large LITERAL entries. We use 60..63 in the high 6 bits to - // encode the number of bytes of length info that follow the opcode. - for (unsigned int extra_bytes = 1; extra_bytes <= 4; extra_bytes++) { - // We set the length field in the lookup table to 1 because extra - // bytes encode len-1. - dst[LITERAL | ((extra_bytes+59) << 2)] = MakeEntry(extra_bytes, 1, 0); - assigned++; - } - - // COPY_1_BYTE_OFFSET. - // - // The tag byte in the compressed data stores len-4 in 3 bits, and - // offset/256 in 5 bits. offset%256 is stored in the next byte. - // - // This format is used for length in range [4..11] and offset in - // range [0..2047] - for (unsigned int len = 4; len < 12; len++) { - for (unsigned int offset = 0; offset < 2048; offset += 256) { - dst[COPY_1_BYTE_OFFSET | ((len-4)<<2) | ((offset>>8)<<5)] = - MakeEntry(1, len, offset>>8); - assigned++; - } - } - - // COPY_2_BYTE_OFFSET. - // Tag contains len-1 in top 6 bits, and offset in next two bytes. - for (unsigned int len = 1; len <= 64; len++) { - dst[COPY_2_BYTE_OFFSET | ((len-1)<<2)] = MakeEntry(2, len, 0); - assigned++; - } - - // COPY_4_BYTE_OFFSET. - // Tag contents len-1 in top 6 bits, and offset in next four bytes. - for (unsigned int len = 1; len <= 64; len++) { - dst[COPY_4_BYTE_OFFSET | ((len-1)<<2)] = MakeEntry(4, len, 0); - assigned++; - } - - // Check that each entry was initialized exactly once. - if (assigned != 256) { - fprintf(stderr, "ComputeTable: assigned only %d of 256\n", assigned); - abort(); - } - for (int i = 0; i < 256; i++) { - if (dst[i] == 0xffff) { - fprintf(stderr, "ComputeTable: did not assign byte %d\n", i); - abort(); - } - } - - if (FLAGS_snappy_dump_decompression_table) { - printf("static const uint16 char_table[256] = {\n "); - for (int i = 0; i < 256; i++) { - printf("0x%04x%s", - dst[i], - ((i == 255) ? "\n" : (((i%8) == 7) ? ",\n " : ", "))); - } - printf("};\n"); - } - - // Check that computed table matched recorded table - for (int i = 0; i < 256; i++) { - if (dst[i] != char_table[i]) { - fprintf(stderr, "ComputeTable: byte %d: computed (%x), expect (%x)\n", - i, static_cast<int>(dst[i]), static_cast<int>(char_table[i])); - abort(); - } - } -} -#endif /* !NDEBUG */ - -// 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_[5]; // Temporary buffer for PeekFast() boundaries - - // 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); - *result |= static_cast<uint32>(c & 0x7f) << 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_; - - // 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 < 5) { \ - ip_ = ip; \ - if (!RefillTag()) return; \ - ip = ip_; \ - } - - MAYBE_REFILL(); - for ( ;; ) { - const unsigned char c = *(reinterpret_cast<const unsigned char*>(ip++)); - - if ((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; - MAYBE_REFILL(); - continue; - } - if (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 uint32 entry = char_table[c]; - const uint32 trailer = LittleEndian::Load32(ip) & wordmask[entry >> 11]; - const uint32 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 uint32 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; - if (n == 0) { - eof_ = true; - 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 = 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 < 5) { - // 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, - uint32 max_len) { - // 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, uncompressed_len, max_len); -} - -template <typename Writer> -static bool InternalUncompressAllTags(SnappyDecompressor* decompressor, - Writer* writer, - uint32 uncompressed_len, - uint32 max_len) { - // Protect against possible DoS attack - if (static_cast<uint64>(uncompressed_len) > max_len) { - return false; - } - - writer->SetExpectedLength(uncompressed_len); - - // Process the entire input - decompressor->DecompressAllTags(writer); - 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(); - 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 = 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 = 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); - } - - delete[] scratch; - delete[] scratch_output; - - return written; -} - -// ----------------------------------------------------------------------- -// 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) { - } - - 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 && space_left >= 16) { - // Fast path, used for the majority (about 95%) of invocations. - UnalignedCopy64(ip, op); - UnalignedCopy64(ip + 8, op + 8); - op_ = op + len; - return true; - } else { - return false; - } - } - - inline bool AppendFromSelf(size_t offset, size_t len) { - char* op = op_; - const size_t space_left = op_limit_ - op; - - if (op - base_ <= offset - 1u) { // -1u catches offset==0 - return false; - } - if (len <= 16 && offset >= 8 && space_left >= 16) { - // Fast path, used for the majority (70-80%) of dynamic invocations. - UnalignedCopy64(op - offset, op); - UnalignedCopy64(op - offset + 8, op + 8); - } else { - if (space_left >= len + kMaxIncrementCopyOverflow) { - IncrementalCopyFastPath(op - offset, op, len); - } else { - if (space_left < len) { - return false; - } - IncrementalCopy(op - offset, op, len); - } - } - - op_ = op + len; - return true; - } -}; - -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, kuint32max); -} - -bool Uncompress(const char* compressed, size_t n, string* uncompressed) { - size_t ulength; - if (!GetUncompressedLength(compressed, n, &ulength)) { - return false; - } - // Protect against possible DoS attack - if ((static_cast<uint64>(ulength) + uncompressed->size()) > - 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() : 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) { - if (produced_ <= offset - 1u) return false; // -1u catches offset==0 - produced_ += len; - return produced_ <= expected_; - } -}; - -bool IsValidCompressedBuffer(const char* compressed, size_t n) { - ByteArraySource reader(compressed, n); - SnappyDecompressionValidator writer; - return InternalUncompress(&reader, &writer, kuint32max); -} - -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 - compressed->resize(MaxCompressedLength(input_length)); - - size_t compressed_length; - RawCompress(input, input_length, string_as_array(compressed), - &compressed_length); - compressed->resize(compressed_length); - return compressed_length; -} - - -} // end namespace snappy - |