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Diffstat (limited to 'main/snappy/snappy-internal.h')
| -rw-r--r-- | main/snappy/snappy-internal.h | 150 |
1 files changed, 150 insertions, 0 deletions
diff --git a/main/snappy/snappy-internal.h b/main/snappy/snappy-internal.h new file mode 100644 index 00000000..c99d3313 --- /dev/null +++ b/main/snappy/snappy-internal.h @@ -0,0 +1,150 @@ +// Copyright 2008 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. +// +// Internals shared between the Snappy implementation and its unittest. + +#ifndef UTIL_SNAPPY_SNAPPY_INTERNAL_H_ +#define UTIL_SNAPPY_SNAPPY_INTERNAL_H_ + +#include "snappy-stubs-internal.h" + +namespace snappy { +namespace internal { + +class WorkingMemory { + public: + WorkingMemory() : large_table_(NULL) { } + ~WorkingMemory() { delete[] large_table_; } + + // Allocates and clears a hash table using memory in "*this", + // stores the number of buckets in "*table_size" and returns a pointer to + // the base of the hash table. + uint16* GetHashTable(size_t input_size, int* table_size); + + private: + uint16 small_table_[1<<10]; // 2KB + uint16* large_table_; // Allocated only when needed + + DISALLOW_COPY_AND_ASSIGN(WorkingMemory); +}; + +// Flat array compression that does not emit the "uncompressed length" +// prefix. Compresses "input" string to the "*op" buffer. +// +// REQUIRES: "input_length <= kBlockSize" +// REQUIRES: "op" points to an array of memory that is at least +// "MaxCompressedLength(input_length)" 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". +char* CompressFragment(const char* input, + size_t input_length, + char* op, + uint16* table, + const int table_size); + +// Return the largest n such that +// +// s1[0,n-1] == s2[0,n-1] +// and n <= (s2_limit - s2). +// +// Does not read *s2_limit or beyond. +// Does not read *(s1 + (s2_limit - s2)) or beyond. +// Requires that s2_limit >= s2. +// +// Separate implementation for x86_64, for speed. Uses the fact that +// x86_64 is little endian. +#if defined(ARCH_K8) +static inline int FindMatchLength(const char* s1, + const char* s2, + const char* s2_limit) { + assert(s2_limit >= s2); + int matched = 0; + + // Find out how long the match is. We loop over the data 64 bits at a + // time until we find a 64-bit block that doesn't match; then we find + // the first non-matching bit and use that to calculate the total + // length of the match. + while (PREDICT_TRUE(s2 <= s2_limit - 8)) { + if (PREDICT_FALSE(UNALIGNED_LOAD64(s2) == UNALIGNED_LOAD64(s1 + matched))) { + s2 += 8; + matched += 8; + } else { + // On current (mid-2008) Opteron models there is a 3% more + // efficient code sequence to find the first non-matching byte. + // However, what follows is ~10% better on Intel Core 2 and newer, + // and we expect AMD's bsf instruction to improve. + uint64 x = UNALIGNED_LOAD64(s2) ^ UNALIGNED_LOAD64(s1 + matched); + int matching_bits = Bits::FindLSBSetNonZero64(x); + matched += matching_bits >> 3; + return matched; + } + } + while (PREDICT_TRUE(s2 < s2_limit)) { + if (PREDICT_TRUE(s1[matched] == *s2)) { + ++s2; + ++matched; + } else { + return matched; + } + } + return matched; +} +#else +static inline int FindMatchLength(const char* s1, + const char* s2, + const char* s2_limit) { + // Implementation based on the x86-64 version, above. + assert(s2_limit >= s2); + int matched = 0; + + while (s2 <= s2_limit - 4 && + UNALIGNED_LOAD32(s2) == UNALIGNED_LOAD32(s1 + matched)) { + s2 += 4; + matched += 4; + } + if (LittleEndian::IsLittleEndian() && s2 <= s2_limit - 4) { + uint32 x = UNALIGNED_LOAD32(s2) ^ UNALIGNED_LOAD32(s1 + matched); + int matching_bits = Bits::FindLSBSetNonZero(x); + matched += matching_bits >> 3; + } else { + while ((s2 < s2_limit) && (s1[matched] == *s2)) { + ++s2; + ++matched; + } + } + return matched; +} +#endif + +} // end namespace internal +} // end namespace snappy + +#endif // UTIL_SNAPPY_SNAPPY_INTERNAL_H_ |