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Hash: A single unified algorithm for hashing floats.

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Attempts to automatically use a binary hash for floats where it's known to
work, and then use the generic hash algorithm as a fallback.

[SVN r80177]
This commit is contained in:
Daniel James
2012-08-24 22:52:42 +00:00
parent f1de575546
commit eec47991f9
4 changed files with 182 additions and 162 deletions
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182
include/boost/functional/hash/detail/hash_float.hpp
View File

@@ -1,5 +1,5 @@
// Copyright 2005-2009 Daniel James.
// Copyright 2005-2012 Daniel James.
// Distributed under the Boost Software License, Version 1.0. (See accompanying
// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
@@ -13,21 +13,19 @@
#include <boost/config.hpp>
#include <boost/functional/hash/detail/float_functions.hpp>
#include <boost/functional/hash/detail/limits.hpp>
#include <boost/utility/enable_if.hpp>
#include <boost/integer/static_log2.hpp>
#include <boost/cstdint.hpp>
#include <boost/assert.hpp>
#include <boost/limits.hpp>
#include <cstring>
// Include hash implementation for the current platform.
// Cygwn
#if defined(__CYGWIN__)
# if defined(__i386__) || defined(_M_IX86)
# include <boost/functional/hash/detail/hash_float_x86.hpp>
# else
# include <boost/functional/hash/detail/hash_float_generic.hpp>
# endif
#else
# include <boost/functional/hash/detail/hash_float_generic.hpp>
#if defined(BOOST_MSVC)
#pragma warning(push)
#if BOOST_MSVC >= 1400
#pragma warning(disable:6294) // Ill-defined for-loop: initial condition does
// not satisfy test. Loop body not executed
#endif
#endif
// Can we use fpclassify?
@@ -50,6 +48,158 @@
# define BOOST_HASH_USE_FPCLASSIFY 0
#endif
namespace boost
{
namespace hash_detail
{
inline void hash_float_combine(std::size_t& seed, std::size_t value)
{
seed ^= value + (seed<<6) + (seed>>2);
}
////////////////////////////////////////////////////////////////////////
// Binary hash function
//
// Only used for floats with known iec559 floats, and certain values in
// numeric_limits
inline std::size_t hash_binary(char* ptr, std::size_t length)
{
std::size_t seed = 0;
if (length >= sizeof(std::size_t)) {
seed = *(std::size_t*) ptr;
length -= sizeof(std::size_t);
ptr += sizeof(std::size_t);
while(length >= sizeof(std::size_t)) {
hash_float_combine(seed, *(std::size_t*) ptr);
length -= sizeof(std::size_t);
ptr += sizeof(std::size_t);
}
}
if (length > 0) {
std::size_t buffer = 0;
std::memcpy(&buffer, ptr, length);
hash_float_combine(seed, buffer);
}
return seed;
}
template <typename Float>
inline std::size_t float_hash_impl(Float v,
BOOST_DEDUCED_TYPENAME boost::enable_if_c<
std::numeric_limits<Float>::is_iec559 &&
std::numeric_limits<Float>::digits == 24 &&
std::numeric_limits<Float>::radix == 2 &&
std::numeric_limits<Float>::max_exponent == 128,
int>::type
)
{
boost::uint32_t* ptr = (boost::uint32_t*)&v;
return (std::size_t) *ptr;
}
template <typename Float>
inline std::size_t float_hash_impl(Float v,
BOOST_DEDUCED_TYPENAME boost::enable_if_c<
std::numeric_limits<Float>::is_iec559 &&
std::numeric_limits<Float>::digits == 53 &&
std::numeric_limits<Float>::radix == 2 &&
std::numeric_limits<Float>::max_exponent == 1024,
int>::type
)
{
return hash_binary((char*) &v, 8);
}
template <typename Float>
inline std::size_t float_hash_impl(Float v,
BOOST_DEDUCED_TYPENAME boost::enable_if_c<
std::numeric_limits<Float>::is_iec559 &&
std::numeric_limits<Float>::digits == 64 &&
std::numeric_limits<Float>::radix == 2 &&
std::numeric_limits<Float>::max_exponent == 16384,
int>::type
)
{
return hash_binary((char*) &v, 10);
}
template <typename Float>
inline std::size_t float_hash_impl(Float v,
BOOST_DEDUCED_TYPENAME boost::enable_if_c<
std::numeric_limits<Float>::is_iec559 &&
std::numeric_limits<Float>::digits == 113 &&
std::numeric_limits<Float>::radix == 2 &&
std::numeric_limits<Float>::max_exponent == 16384,
int>::type
)
{
return hash_binary((char*) &v, 16);
}
////////////////////////////////////////////////////////////////////////
// Portable hash function
//
// Used as a fallback when the binary hash function isn't supported.
template <class T>
inline std::size_t float_hash_impl2(T v)
{
boost::hash_detail::call_frexp<T> frexp;
boost::hash_detail::call_ldexp<T> ldexp;
int exp = 0;
v = frexp(v, &exp);
// A postive value is easier to hash, so combine the
// sign with the exponent and use the absolute value.
if(v < 0) {
v = -v;
exp += limits<T>::max_exponent -
limits<T>::min_exponent;
}
v = ldexp(v, limits<std::size_t>::digits);
std::size_t seed = static_cast<std::size_t>(v);
v -= static_cast<T>(seed);
// ceiling(digits(T) * log2(radix(T))/ digits(size_t)) - 1;
std::size_t const length
= (limits<T>::digits *
boost::static_log2<limits<T>::radix>::value
+ limits<std::size_t>::digits - 1)
/ limits<std::size_t>::digits;
for(std::size_t i = 0; i != length; ++i)
{
v = ldexp(v, limits<std::size_t>::digits);
std::size_t part = static_cast<std::size_t>(v);
v -= static_cast<T>(part);
hash_float_combine(seed, part);
}
hash_float_combine(seed, exp);
return seed;
}
#if !defined(BOOST_HASH_DETAIL_TEST_WITHOUT_GENERIC)
template <class T>
inline std::size_t float_hash_impl(T v, ...)
{
typedef BOOST_DEDUCED_TYPENAME select_hash_type<T>::type type;
return float_hash_impl2(static_cast<type>(v));
}
#endif
}
}
#if BOOST_HASH_USE_FPCLASSIFY
#include <boost/config/no_tr1/cmath.hpp>
@@ -71,7 +221,7 @@ namespace boost
return (std::size_t)(-3);
case FP_NORMAL:
case FP_SUBNORMAL:
return float_hash_impl(v);
return float_hash_impl(v, 0);
default:
BOOST_ASSERT(0);
return 0;
@@ -103,7 +253,7 @@ namespace boost
template <class T>
inline std::size_t float_hash_value(T v)
{
return boost::hash_detail::is_zero(v) ? 0 : float_hash_impl(v);
return boost::hash_detail::is_zero(v) ? 0 : float_hash_impl(v, 0);
}
}
}
@@ -112,4 +262,8 @@ namespace boost
#undef BOOST_HASH_USE_FPCLASSIFY
#if defined(BOOST_MSVC)
#pragma warning(pop)
#endif
#endif

91
include/boost/functional/hash/detail/hash_float_generic.hpp
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@@ -1,91 +0,0 @@
// Copyright 2005-2009 Daniel James.
// Distributed under the Boost Software License, Version 1.0. (See accompanying
// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
// A general purpose hash function for non-zero floating point values.
#if !defined(BOOST_FUNCTIONAL_HASH_DETAIL_HASH_FLOAT_GENERIC_HEADER)
#define BOOST_FUNCTIONAL_HASH_DETAIL_HASH_FLOAT_GENERIC_HEADER
#include <boost/functional/hash/detail/float_functions.hpp>
#include <boost/integer/static_log2.hpp>
#include <boost/functional/hash/detail/limits.hpp>
#if defined(_MSC_VER) && (_MSC_VER >= 1020)
# pragma once
#endif
#if defined(BOOST_MSVC)
#pragma warning(push)
#if BOOST_MSVC >= 1400
#pragma warning(disable:6294) // Ill-defined for-loop: initial condition does
// not satisfy test. Loop body not executed
#endif
#endif
namespace boost
{
namespace hash_detail
{
inline void hash_float_combine(std::size_t& seed, std::size_t value)
{
seed ^= value + (seed<<6) + (seed>>2);
}
template <class T>
inline std::size_t float_hash_impl2(T v)
{
boost::hash_detail::call_frexp<T> frexp;
boost::hash_detail::call_ldexp<T> ldexp;
int exp = 0;
v = frexp(v, &exp);
// A postive value is easier to hash, so combine the
// sign with the exponent and use the absolute value.
if(v < 0) {
v = -v;
exp += limits<T>::max_exponent -
limits<T>::min_exponent;
}
v = ldexp(v, limits<std::size_t>::digits);
std::size_t seed = static_cast<std::size_t>(v);
v -= static_cast<T>(seed);
// ceiling(digits(T) * log2(radix(T))/ digits(size_t)) - 1;
std::size_t const length
= (limits<T>::digits *
boost::static_log2<limits<T>::radix>::value
+ limits<std::size_t>::digits - 1)
/ limits<std::size_t>::digits;
for(std::size_t i = 0; i != length; ++i)
{
v = ldexp(v, limits<std::size_t>::digits);
std::size_t part = static_cast<std::size_t>(v);
v -= static_cast<T>(part);
hash_float_combine(seed, part);
}
hash_float_combine(seed, exp);
return seed;
}
template <class T>
inline std::size_t float_hash_impl(T v)
{
typedef BOOST_DEDUCED_TYPENAME select_hash_type<T>::type type;
return float_hash_impl2(static_cast<type>(v));
}
}
}
#if defined(BOOST_MSVC)
#pragma warning(pop)
#endif
#endif

56
include/boost/functional/hash/detail/hash_float_x86.hpp
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@@ -1,56 +0,0 @@
// Copyright 2005-2009 Daniel James.
// Distributed under the Boost Software License, Version 1.0. (See accompanying
// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
// A non-portable hash function form non-zero floats on x86.
//
// Even if you're on an x86 platform, this might not work if their floating
// point isn't set up as this expects. So this should only be used if it's
// absolutely certain that it will work.
#if !defined(BOOST_FUNCTIONAL_HASH_DETAIL_HASH_FLOAT_X86_HEADER)
#define BOOST_FUNCTIONAL_HASH_DETAIL_HASH_FLOAT_X86_HEADER
#include <boost/cstdint.hpp>
#if defined(_MSC_VER) && (_MSC_VER >= 1020)
# pragma once
#endif
namespace boost
{
namespace hash_detail
{
inline void hash_float_combine(std::size_t& seed, std::size_t value)
{
seed ^= value + (seed<<6) + (seed>>2);
}
inline std::size_t float_hash_impl(float v)
{
boost::uint32_t* ptr = (boost::uint32_t*)&v;
std::size_t seed = *ptr;
return seed;
}
inline std::size_t float_hash_impl(double v)
{
boost::uint32_t* ptr = (boost::uint32_t*)&v;
std::size_t seed = *ptr++;
hash_float_combine(seed, *ptr);
return seed;
}
inline std::size_t float_hash_impl(long double v)
{
boost::uint32_t* ptr = (boost::uint32_t*)&v;
std::size_t seed = *ptr++;
hash_float_combine(seed, *ptr++);
hash_float_combine(seed, *(boost::uint16_t*)ptr);
return seed;
}
}
}
#endif

15
test/Jamfile.v2
View File

@@ -1,5 +1,5 @@
# Copyright 2005-2011 Daniel James.
# Copyright 2005-2012 Daniel James.
# Distributed under the Boost Software License, Version 1.0. (See accompanying
# file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
@@ -66,4 +66,17 @@ test-suite functional/hash_no_ext
[ run link_test.cpp link_test_2.cpp : : : <define>BOOST_HASH_NO_EXTENSIONS : no_ext_link_test ]
;
# Tests to see if the floating point hash is using the binary hash.
# Not run normally because on some platforms these should fail.
test-suite functional/hash_no_generic_float
:
[ run hash_float_test.cpp
: : : <define>BOOST_HASH_DETAIL_TEST_WITHOUT_GENERIC
: hash_float_test_no_generic ]
[ run hash_long_double_test.cpp
: : : <define>BOOST_HASH_DETAIL_TEST_WITHOUT_GENERIC
: hash_long_double_test_no_generic ]
;
explicit functional/hash_no_generic_float ;
build-project ../examples ;