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// Copyright 2018 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#include "components/variations/variations_murmur_hash.h"
#include "base/compiler_specific.h"
#include "base/logging.h"
#include "base/sys_byteorder.h"
#include "build/build_config.h"
#if !(defined(ARCH_CPU_LITTLE_ENDIAN) || defined(ARCH_CPU_BIG_ENDIAN))
#error "unknown endianness"
#endif
namespace variations {
namespace internal {
// static
std::vector<uint32_t> VariationsMurmurHash::StringToLE32(
const std::string& data) {
const size_t data_size = data.size();
const size_t word_num = (data_size + 3) / 4; // data_size / 4, rounding up
std::vector<uint32_t> words(word_num, 0);
DCHECK_GE(words.size() * sizeof(uint32_t), data_size * sizeof(char));
memcpy(words.data(), data.data(), data_size);
#if defined(ARCH_CPU_BIG_ENDIAN)
// When packing chars into uint32_t, "abcd" may become 0x61626364 (big endian)
// or 0x64636261 (little endian). If big endian, swap everything, so we get
// the same values across platforms.
for (auto it = words.begin(); it != words.end(); ++it)
*it = base::ByteSwapToLE32(*it);
#endif // defined(ARCH_CPU_BIG_ENDIAN)
return words;
}
// static
uint32_t VariationsMurmurHash::Hash(const std::vector<uint32_t>& data,
size_t length) {
DCHECK_LE(length, data.size() * sizeof(uint32_t));
uint32_t h1 = 0;
// body
size_t num_full_blocks = length / sizeof(uint32_t);
for (size_t i = 0; i < num_full_blocks; i++) {
uint32_t k1 = data[i];
k1 *= c1;
k1 = RotateLeft(k1, 15);
k1 *= c2;
h1 ^= k1;
h1 = RotateLeft(h1, 13);
h1 = h1 * 5 + 0xe6546b64;
}
// tail
uint32_t k1 = 0;
switch (length & 3) {
case 3:
k1 |= data[num_full_blocks] & 0xFF0000;
FALLTHROUGH;
case 2:
k1 |= data[num_full_blocks] & 0xFF00;
FALLTHROUGH;
case 1:
k1 |= data[num_full_blocks] & 0xFF;
}
k1 *= c1;
k1 = RotateLeft(k1, 15);
k1 *= c2;
h1 ^= k1;
// finalization
h1 ^= length;
h1 = FinalMix(h1);
return h1;
}
} // namespace internal
} // namespace variations
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