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Remove optimization which causes 0.5 to hash to 0. Refs #4038.

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I have an internal requirement the 0 hashes to 0, a better solution
might be to remove that, put the optimization back and hash 0 to another
value. Or alternatively, use the main combine function instead.

[SVN r60805]
This commit is contained in:
Daniel James
2010-03-24 08:49:00 +00:00
parent 77f856e3cf
commit 733422d1b9
2 changed files with 20 additions and 5 deletions
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8
include/boost/functional/hash/detail/hash_float_generic.hpp
View File

@@ -51,17 +51,15 @@ namespace boost
limits<T>::min_exponent;
}
// The result of frexp is always between 0.5 and 1, so its
// top bit will always be 1. Subtract by 0.5 to remove that.
v -= T(0.5);
v = ldexp(v, limits<std::size_t>::digits + 1);
v = ldexp(v, limits<std::size_t>::digits);
std::size_t seed = static_cast<std::size_t>(v);
v -= 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 - 1)
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)

17
test/hash_float_test.hpp
View File

@@ -79,6 +79,11 @@ void float_tests(char const* name, T* = 0)
BOOST_TEST(x1(minus_zero) == HASH_NAMESPACE::hash_value(minus_zero));
#endif
BOOST_TEST(x1(zero) != x1(0.5));
BOOST_TEST(x1(minus_zero) != x1(0.5));
BOOST_TEST(x1(0.5) != x1(-0.5));
BOOST_TEST(x1(1) != x1(-1));
using namespace std;
// Doing anything with infinity causes borland to crash.
@@ -176,6 +181,12 @@ void float_tests(char const* name, T* = 0)
BOOST_TEST(half_max != three_quarter_max);
BOOST_TEST(quarter_max != three_quarter_max);
BOOST_TEST(max != -max);
BOOST_TEST(half_max != -half_max);
BOOST_TEST(quarter_max != -quarter_max);
BOOST_TEST(three_quarter_max != -three_quarter_max);
#if defined(TEST_EXTENSIONS)
BOOST_TEST(x1(max) == HASH_NAMESPACE::hash_value(max));
BOOST_TEST(x1(half_max) == HASH_NAMESPACE::hash_value(half_max));
@@ -197,6 +208,12 @@ void float_tests(char const* name, T* = 0)
BOOST_TEST(x1(half_max) != x1(three_quarter_max));
BOOST_TEST(x1(three_quarter_max) == x1(three_quarter_max));
BOOST_TEST(x1(max) != x1(-max));
BOOST_TEST(x1(half_max) != x1(-half_max));
BOOST_TEST(x1(quarter_max) != x1(-quarter_max));
BOOST_TEST(x1(three_quarter_max) != x1(-three_quarter_max));
// Intel with gcc stdlib sometimes segfaults on calls to asin and acos.
#if !((defined(__INTEL_COMPILER) || defined(__ICL) || \
defined(__ICC) || defined(__ECC)) && \