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// Copyright 2016 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
// Based on "v8/src/base/functional.cc".
// See: Thomas Wang, Integer Hash Functions.
// https://gist.github.com/badboy/6267743
// TODO(pkalinnikov): Consider moving the implementation into base/.
#ifndef COMPONENTS_URL_PATTERN_INDEX_UINT64_HASHER_H_
#define COMPONENTS_URL_PATTERN_INDEX_UINT64_HASHER_H_
#include <stddef.h>
#include <stdint.h>
#include <type_traits>
namespace url_pattern_index {
template <typename T>
requires(sizeof(T) == 4)
T Uint64Hash(uint64_t v) {
// "64 bit to 32 bit Hash Functions"
v = ~v + (v << 18); // v = (v << 18) - v - 1;
v = v ^ (v >> 31);
v = v * 21; // v = (v + (v << 2)) + (v << 4);
v = v ^ (v >> 11);
v = v + (v << 6);
v = v ^ (v >> 22);
return static_cast<T>(v);
}
template <typename T>
requires(sizeof(T) == 8)
T Uint64Hash(uint64_t v) {
// "64 bit Mix Functions"
v = ~v + (v << 21); // v = (v << 21) - v - 1;
v = v ^ (v >> 24);
v = (v + (v << 3)) + (v << 8); // v * 265
v = v ^ (v >> 14);
v = (v + (v << 2)) + (v << 4); // v * 21
v = v ^ (v >> 28);
v = v + (v << 31);
return static_cast<T>(v);
}
// Note: A Uint64ToUint64Hasher variant is currently not needed.
// Note: Be careful about a variant that hashes differently in 32-bit vs. 64-bit
// processes (i.e., using |size_t| where the below uses |uint32_t|). Such a
// variant will break compatibility for tables that are built and accessed in
// processes of differing bitness, which is a real-world concern for users of
// this component (see crbug.com/1174797 for details).
class Uint64ToUint32Hasher {
public:
uint32_t operator()(uint64_t v) const { return Uint64Hash<uint32_t>(v); }
};
} // namespace url_pattern_index
#endif // COMPONENTS_URL_PATTERN_INDEX_UINT64_HASHER_H_
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