diff options
Diffstat (limited to 'base/hash.h')
| -rw-r--r-- | base/hash.h | 81 |
1 files changed, 0 insertions, 81 deletions
diff --git a/base/hash.h b/base/hash.h index d5dc549..ed8d9fd 100644 --- a/base/hash.h +++ b/base/hash.h @@ -10,7 +10,6 @@ #include <limits> #include <string> -#include <utility> #include "base/base_export.h" #include "base/logging.h" @@ -36,86 +35,6 @@ inline uint32_t Hash(const std::string& str) { return Hash(str.data(), str.size()); } -// 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 -// -// Contact danakj@chromium.org for any questions. -inline size_t HashInts32(uint32_t value1, uint32_t value2) { - uint64_t value1_64 = value1; - uint64_t hash64 = (value1_64 << 32) | value2; - - if (sizeof(size_t) >= sizeof(uint64_t)) - return static_cast<size_t>(hash64); - - uint64_t odd_random = 481046412LL << 32 | 1025306955LL; - uint32_t shift_random = 10121U << 16; - - hash64 = hash64 * odd_random + shift_random; - size_t high_bits = static_cast<size_t>( - hash64 >> (8 * (sizeof(uint64_t) - sizeof(size_t)))); - return high_bits; -} - -// 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. -inline size_t HashInts64(uint64_t value1, uint64_t value2) { - uint32_t short_random1 = 842304669U; - uint32_t short_random2 = 619063811U; - uint32_t short_random3 = 937041849U; - uint32_t short_random4 = 3309708029U; - - uint32_t value1a = static_cast<uint32_t>(value1 & 0xffffffff); - uint32_t value1b = static_cast<uint32_t>((value1 >> 32) & 0xffffffff); - uint32_t value2a = static_cast<uint32_t>(value2 & 0xffffffff); - uint32_t value2b = static_cast<uint32_t>((value2 >> 32) & 0xffffffff); - - uint64_t product1 = static_cast<uint64_t>(value1a) * short_random1; - uint64_t product2 = static_cast<uint64_t>(value1b) * short_random2; - uint64_t product3 = static_cast<uint64_t>(value2a) * short_random3; - uint64_t product4 = static_cast<uint64_t>(value2b) * short_random4; - - uint64_t hash64 = product1 + product2 + product3 + product4; - - if (sizeof(size_t) >= sizeof(uint64_t)) - return static_cast<size_t>(hash64); - - uint64_t odd_random = 1578233944LL << 32 | 194370989LL; - uint32_t shift_random = 20591U << 16; - - hash64 = hash64 * odd_random + shift_random; - size_t high_bits = static_cast<size_t>( - hash64 >> (8 * (sizeof(uint64_t) - sizeof(size_t)))); - return high_bits; -} - -template<typename T1, typename T2> -inline size_t HashInts(T1 value1, T2 value2) { - // This condition is expected to be compile-time evaluated and optimised away - // in release builds. - if (sizeof(T1) > sizeof(uint32_t) || (sizeof(T2) > sizeof(uint32_t))) - return HashInts64(value1, value2); - - return HashInts32(value1, value2); -} - -// A templated hasher for pairs of integer types. -template<typename T> struct IntPairHash; - -template<typename Type1, typename Type2> -struct IntPairHash<std::pair<Type1, Type2>> { - size_t operator()(std::pair<Type1, Type2> value) const { - return HashInts(value.first, value.second); - } -}; - } // namespace base #endif // BASE_HASH_H_ |
