When testing GNU MPFR with ICX 2021.1 Beta 20200715, the test tset_float128 failed. Here's a simple testcase:
#include <stdio.h>
void foo (__float128 d)
{
int i;
__float128 p[8], q[8];
if (d >= 1.0)
{
p[0] = 2.0;
q[0] = 0.5;
printf ("q[0] = %a\n", (double) q[0]);
for (i = 0; i < 13 && d >= p[i]; i++)
{
printf ("q[%d] = %a\n", i, (double) q[i]);
p[i+1] = p[i] * p[i];
q[i+1] = q[i] * q[i];
}
for (; i >= 0; i--)
if (d >= p[i])
d *= q[i];
}
else if (d < 0.5)
{
p[0] = 2.0;
q[0] = 0.5;
for (i = 0; i < 13 && d < q[i]; i++)
{
p[i+1] = p[i] * p[i];
q[i+1] = q[i] * q[i];
}
for (; i >= 0; i--)
while (d < q[i])
d *= p[i];
}
return;
}
int main (void)
{
volatile __float128 d = 65536;
foo (d);
return 0;
}
When I compile this code with optimizations (i.e. not with -O0), I get:
q[0] = 0x1p-1
q[0] = 0x0p+0
q[1] = 0x0p+0
q[2] = 0x0p+0
q[3] = 0x0p+0
q[4] = 0x0p+0
instead of
q[0] = 0x1p-1
q[0] = 0x1p-1
q[1] = 0x1p-2
q[2] = 0x1p-4
q[3] = 0x1p-8
q[4] = 0x1p-16
