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// Copyright 2008 Google Inc. All Rights Reserved.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
//
// 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) {
DCHECK_GE(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.
DCHECK_GE(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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