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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 be0a60760c
commit a7d58c92b3
2 changed files with 20 additions and 5 deletions
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include/boost/functional/hash/detail/hash_float_generic.hpp
+3 -5
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@@ -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)