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Don't use std::__clz in 'test/support/hexfloat.h'. 

std::__clz is a libc++ specific function so it can't be used in the test suite.
This patch implements a dumb "count leading zeros" implementation within
hexfloat itself.

This patch also fixes UB since the output of `__builtin_clz(0)` is undefined
according to the GCC docs.

llvm-svn: 268354
This commit is contained in:
Eric Fiselier 2016-05-03 02:04:26 +00:00
parent c357278a38
commit 43a10eb637
1 changed files with 16 additions and 4 deletions
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20
libcxx/test/support/hexfloat.h
View File

@ -15,7 +15,6 @@
#ifndef HEXFLOAT_H
#define HEXFLOAT_H
#include <algorithm>
#include <cmath>
#include <climits>
@ -23,13 +22,26 @@ template <class T>
class hexfloat
{
T value_;
static int CountLeadingZeros(unsigned long long n) {
const std::size_t Digits = sizeof(unsigned long long) * CHAR_BIT;
const unsigned long long TopBit = 1ull << (Digits - 1);
if (n == 0) return Digits;
int LeadingZeros = 0;
while ((n & TopBit) == 0) {
++LeadingZeros;
n <<= 1;
}
return LeadingZeros;
}
public:
hexfloat(long long m1, unsigned long long m0, int exp)
{
const std::size_t n = sizeof(unsigned long long) * CHAR_BIT;
const std::size_t Digits = sizeof(unsigned long long) * CHAR_BIT;
int s = m1 < 0 ? -1 : 1;
value_ = std::ldexp(m1 + s * std::ldexp(T(m0), -static_cast<int>(n -
std::__clz(m0)/4*4)), exp);
int exp2 = -static_cast<int>(Digits - CountLeadingZeros(m0)/4*4);
value_ = std::ldexp(m1 + s * std::ldexp(T(m0), exp2), exp);
}
operator T() const {return value_;}