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- // 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_
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