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// Copyright (c) 2012 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.
//
// Defines methods for hashing a pair of integers.
#ifndef CC_BASE_HASH_PAIR_H_
#define CC_BASE_HASH_PAIR_H_
#include "base/hash_tables.h"
#if defined(COMPILER_MSVC)
#define DEFINE_PAIR_HASH_FUNCTION_START(type1, type2) \
template<> \
inline std::size_t hash_value<std::pair<type1, type2> >( \
const std::pair<type1, type2>& value)
#define DEFINE_PAIR_HASH_FUNCTION_END()
#elif defined(COMPILER_GCC)
#define DEFINE_PAIR_HASH_FUNCTION_START(type1, type2) \
template<> \
struct hash<std::pair<type1, type2> > { \
std::size_t operator()(std::pair<type1, type2> value) const
#define DEFINE_PAIR_HASH_FUNCTION_END() \
};
#else
#error define DEFINE_PAIR_HASH_FUNCTION_START for your compiler
#endif // COMPILER
namespace BASE_HASH_NAMESPACE {
// Implement hashing for pairs of at-most 32 bit integer values.
// When size_t is 32 bits, we turn the 64-bit hash code into 32 bits by using
// multiply-add hashing. This algorithm, as described in
// Theorem 4.3.3 of the thesis "Über die Komplexität der Multiplikation in
// eingeschränkten Branchingprogrammmodellen" by Woelfel, is:
//
// h32(x32, y32) = (h64(x32, y32) * rand_odd64 + rand16 * 2^16) % 2^64 / 2^32
#define DEFINE_32BIT_PAIR_HASH(type1, type2) \
DEFINE_PAIR_HASH_FUNCTION_START(type1, type2) { \
uint64 first = value.first; \
uint32 second = value.second; \
uint64 hash64 = (first << 32) | second; \
\
if (sizeof(std::size_t) >= sizeof(uint64)) \
return static_cast<std::size_t>(hash64); \
\
uint64 odd_random = 481046412LL << 32 | 1025306954LL; \
uint32 shift_random = 10121U << 16; \
\
hash64 = hash64 * odd_random + shift_random; \
std::size_t high_bits = static_cast<std::size_t>( \
hash64 >> (sizeof(uint64) - sizeof(std::size_t))); \
return high_bits; \
} \
DEFINE_PAIR_HASH_FUNCTION_END();
DEFINE_32BIT_PAIR_HASH(short, short);
DEFINE_32BIT_PAIR_HASH(short, unsigned short);
DEFINE_32BIT_PAIR_HASH(short, int);
DEFINE_32BIT_PAIR_HASH(short, unsigned);
DEFINE_32BIT_PAIR_HASH(unsigned short, short);
DEFINE_32BIT_PAIR_HASH(unsigned short, unsigned short);
DEFINE_32BIT_PAIR_HASH(unsigned short, int);
DEFINE_32BIT_PAIR_HASH(unsigned short, unsigned);
DEFINE_32BIT_PAIR_HASH(int, short);
DEFINE_32BIT_PAIR_HASH(int, unsigned short);
DEFINE_32BIT_PAIR_HASH(int, int);
DEFINE_32BIT_PAIR_HASH(int, unsigned);
DEFINE_32BIT_PAIR_HASH(unsigned, short);
DEFINE_32BIT_PAIR_HASH(unsigned, unsigned short);
DEFINE_32BIT_PAIR_HASH(unsigned, int);
DEFINE_32BIT_PAIR_HASH(unsigned, unsigned);
#undef DEFINE_32BIT_PAIR_HASH
// Implement hashing for pairs of up-to 64-bit integer values.
// We use the compound integer hash method to produce a 64-bit hash code, by
// breaking the two 64-bit inputs into 4 32-bit values:
// http://opendatastructures.org/versions/edition-0.1d/ods-java/node33.html#SECTION00832000000000000000
// Then we reduce our result to 32 bits if required, similar to above.
#define DEFINE_64BIT_PAIR_HASH(type1, type2) \
DEFINE_PAIR_HASH_FUNCTION_START(type1, type2) { \
uint32 short_random1 = 842304669U; \
uint32 short_random2 = 619063811U; \
uint32 short_random3 = 937041849U; \
uint32 short_random4 = 3309708029U; \
\
uint64 value1 = value.first; \
uint64 value2 = value.second; \
uint32 value1a = static_cast<uint32>(value1 & 0xffffffff); \
uint32 value1b = static_cast<uint32>((value1 >> 32) & 0xffffffff); \
uint32 value2a = static_cast<uint32>(value2 & 0xffffffff); \
uint32 value2b = static_cast<uint32>((value2 >> 32) & 0xffffffff); \
\
uint64 product1 = static_cast<uint64>(value1a) * short_random1; \
uint64 product2 = static_cast<uint64>(value1b) * short_random2; \
uint64 product3 = static_cast<uint64>(value2a) * short_random3; \
uint64 product4 = static_cast<uint64>(value2b) * short_random4; \
\
uint64 hash64 = product1 + product2 + product3 + product4; \
\
if (sizeof(std::size_t) >= sizeof(uint64)) \
return static_cast<std::size_t>(hash64); \
\
uint64 odd_random = 1578233944LL << 32 | 194370989LL; \
uint32 shift_random = 20591U << 16; \
\
hash64 = hash64 * odd_random + shift_random; \
std::size_t high_bits = static_cast<std::size_t>( \
hash64 >> (sizeof(uint64) - sizeof(std::size_t))); \
return high_bits; \
} \
DEFINE_PAIR_HASH_FUNCTION_END();
DEFINE_64BIT_PAIR_HASH(short, int64);
DEFINE_64BIT_PAIR_HASH(short, uint64);
DEFINE_64BIT_PAIR_HASH(unsigned short, int64);
DEFINE_64BIT_PAIR_HASH(unsigned short, uint64);
DEFINE_64BIT_PAIR_HASH(int, int64);
DEFINE_64BIT_PAIR_HASH(int, uint64);
DEFINE_64BIT_PAIR_HASH(unsigned, int64);
DEFINE_64BIT_PAIR_HASH(unsigned, uint64);
DEFINE_64BIT_PAIR_HASH(int64, short);
DEFINE_64BIT_PAIR_HASH(int64, unsigned short);
DEFINE_64BIT_PAIR_HASH(int64, int);
DEFINE_64BIT_PAIR_HASH(int64, unsigned);
DEFINE_64BIT_PAIR_HASH(int64, int64);
DEFINE_64BIT_PAIR_HASH(int64, uint64);
DEFINE_64BIT_PAIR_HASH(uint64, short);
DEFINE_64BIT_PAIR_HASH(uint64, unsigned short);
DEFINE_64BIT_PAIR_HASH(uint64, int);
DEFINE_64BIT_PAIR_HASH(uint64, unsigned);
DEFINE_64BIT_PAIR_HASH(uint64, int64);
DEFINE_64BIT_PAIR_HASH(uint64, uint64);
#undef DEFINE_64BIT_PAIR_HASH
}
#undef DEFINE_PAIR_HASH_FUNCTION_START
#undef DEFINE_PAIR_HASH_FUNCTION_END
#endif // CC_BASE_HASH_PAIR_H_
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