https://gcc.gnu.org/bugzilla/show_bug.cgi?id=88931
Bug ID: 88931
Summary: Failed to convert int128 to float/double with
round=FE_UPWARD/FE_TOWARDZERO
Product: gcc
Version: 9.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: libgcc
Assignee: unassigned at gcc dot gnu.org
Reporter: hjl.tools at gmail dot com
Target Milestone: ---
[hjl@gnu-cfl-1 float128-5]$ cat x.c
#include <fenv.h>
#include <stdio.h>
#include <quadmath.h>
#pragma STDC FENV_ACCESS ON
#define ROUNDING(r) { r, #r }
int
main (void)
{
char buf[128];
union
{
long long ll[2];
__int128 q;
} u = { 0xdLL, 0x8000000000000000LL };
int i;
struct
{
int r;
const char *s;
} round[] =
{
ROUNDING (FE_DOWNWARD),
ROUNDING (FE_UPWARD),
ROUNDING (FE_TOWARDZERO),
ROUNDING (FE_TONEAREST)
};
for (i = 0; i < sizeof (round) / sizeof (round[0]); i++) {
fesetround(round[i].r);
float f = (float) u.q;
double d = (double) u.q;
__float128 q = (__float128) u.q;
printf("fegetround=%d: %d, %s\n",
fegetround(), round[i].r, round[i].s);
printf("f=%f\t%x\n", f, *(int*)&f);
printf("d=%lf\t%llx\n", d, *(long long*)&d);
quadmath_snprintf(buf, 128, "%Qf", 100, q);
printf("q=%s\t%016llx%016llx\n",
buf, *((long long *)&q + 1), *(long long *)&q);
}
return 0;
}
[hjl@gnu-cfl-1 float128-5]$ make
gcc -std=c99 -fno-strict-aliasing -g -c -o x.o x.c
gcc -o x x.o -lm -lquadmath
./x
fegetround=1024: 1024, FE_DOWNWARD
f=-170141183460469231731687303715884105728.000000 ff000000
d=-170141183460469231731687303715884105728.000000 c7e0000000000000
q=-170141183460469231731687303715884105728.000000
c07e0000000000000000000000000000
fegetround=2048: 2048, FE_UPWARD
f=-170141183460469231731687303715884105728.000000 ff000000
d=-170141183460469231731687303715884105728.000000 c7e0000000000000
q=-170141183460469231731687303715884089344.000000
c07dffffffffffffffffffffffffffff
fegetround=3072: 3072, FE_TOWARDZERO
f=-170141183460469231731687303715884105728.000000 ff000000
d=-170141183460469231731687303715884105728.000000 c7e0000000000000
q=-170141183460469231731687303715884089344.000000
c07dffffffffffffffffffffffffffff
fegetround=0: 0, FE_TONEAREST
f=-170141183460469231731687303715884105728.000000 ff000000
d=-170141183460469231731687303715884105728.000000 c7e0000000000000
q=-170141183460469231731687303715884105728.000000
c07e0000000000000000000000000000
[hjl@gnu-cfl-1 float128-5]$
For FE_UPWARD and FE_TOWARDZERO, float should be feffffff and double
should be c7dfffffffffffff.
