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float: use ULP based comparison

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This commit is contained in:
Danny Robson 2015-01-21 23:32:06 +11:00
parent f64e232201
commit ca6fa4ad3e
2 changed files with 48 additions and 10 deletions
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56
float.cpp
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@ -76,22 +76,58 @@ ieee_float<E, S>::operator==(floating_t _floating) const {
#include <iostream>
//template <unsigned int E, unsigned int S>
//bool
//ieee_float<E, S>::almost_equal (floating_t a,
// floating_t b) {
// // Static cast to avoid integer casting warnings when using uint16_t for half
// static const floating_t epsilon = static_cast<floating_t> (0.001);
// const floating_t diff = static_cast<floating_t> (std::fabs (a - b));
//
// // * Use an exact equality first so that infinities are not indirectly compared. This would generate NaNs in the diff.
// // * Do not use gte or lte. This stops an infinite from making infinities on both sides of the inequality.
// return exactly_equal (a, b) ||
// diff < epsilon * std::fabs (a) ||
// diff < epsilon * std::fabs (b);
//}
template <unsigned int E, unsigned int S>
bool
ieee_float<E, S>::almost_equal (floating_t a,
floating_t b) {
// Static cast to avoid integer casting warnings when using uint16_t for half
static const floating_t epsilon = static_cast<floating_t> (0.001);
const floating_t diff = static_cast<floating_t> (std::fabs (a - b));
// * Use an exact equality first so that infinities are not indirectly compared. This would generate NaNs in the diff.
// * Do not use gte or lte. This stops an infinite from making infinities on both sides of the inequality.
return exactly_equal (a, b) ||
diff < epsilon * std::fabs (a) ||
diff < epsilon * std::fabs (b);
floating_t b)
{
return almost_equal (a, b, 10000);
}
template <unsigned int E, unsigned int S>
bool
ieee_float<E, S>::almost_equal (floating_t _a,
floating_t _b,
uint_t ulps)
{
union {
floating_t f;
sint_t s;
} a, b;
a.f = _a;
b.f = _b;
if (std::isnan (a.f) || std::isnan (b.f))
return false;
if (a.s == b.s)
return true;
uint_t diff = std::abs (a.s - b.s);
std::cerr << "diff: " << diff << '\n';
return diff <= ulps;
}
template class ieee_float< 5, 10>; // ieee_half
template class ieee_float< 8, 23>; // ieee_single;
template class ieee_float<11, 52>; // ieee_double;

2
float.hpp
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@ -14,6 +14,7 @@ class ieee_float {
static const unsigned int BIAS = (1 << (EXPONENT - 1)) - 1;
typedef typename bits_type<TOTAL_BITS>::sint sint_t;
typedef typename bits_type<TOTAL_BITS>::uint uint_t;
typedef typename bits_type<TOTAL_BITS>::floating floating_t;
@ -50,6 +51,7 @@ class ieee_float {
bool operator== (floating_t) const;
static bool almost_equal (floating_t, floating_t);
static bool almost_equal (floating_t, floating_t, uint_t ulps);
};