Hi Gianfranco, >> I quickly looked at the test >> setRoundingMode(TO_POSINF); >> check(getRoundingMode() = TO_POSINF); >> val pos = 1.0/3.0; >> check(pos * 3.0 > 1.0); >> val neg = ~1.0/3.0; >> check(neg * 3.0 > ~1.0); >> >> >> well, I'm not sure the test is correct, I mean, you might have the exact 1.0 >> value too > > 1/3 can’t be represented exactly, so when rounding to +Inf, you get a little > bit more than 1/3. 3 can be represented exactly, so 3 * 1/3 is a little more > than 1, and since the rounding mode is set to +Inf it should therefore round > to a little over 1. I’m pretty sure the test is correct; certainly it works > on every other supported platform.
I just wrote a test program (modified from when I was debugging and fixing
qemu’s ppc rounding mode...):
#include <fenv.h>
#include <stdio.h>
int main(int argc, char **argv) {
int ret;
ret = fegetround();
printf("Current rounding: %d\n", ret);
ret = fesetround(FE_UPWARD);
printf("Setting to FE_UPWARD (%d): %d\n", FE_UPWARD, ret);
ret = fegetround();
printf("Current rounding: %d\n", ret);
double one = 1.0;
double three = 3.0;
double third = one / three;
printf("1.0 / 3.0: %.18f\n", third);
double aboutOne = third * 3.0;
printf("1.0 / 3.0 * 1.0: %.18f\n", aboutOne);
ret = fegetround();
printf("Current rounding: %d\n", ret);
return 0;
}
On amd64:
Current rounding: 0
Setting to FE_UPWARD (2048): 0
Current rounding: 2048
1.0 / 3.0: 0.333333333333333371
1.0 / 3.0 * 1.0: 1.000000000000000223
Current rounding: 2048
On armel:
Current rounding: 0
Setting to FE_UPWARD (4194304): 0
Current rounding: 4194304
Current rounding: 4194304
1.0 / 3.0: 0.333333333333333315
1.0 / 3.0 * 1.0: 1.000000000000000000
Besides FE_UPWARD having a different value (given that it’s platform-specific),
armel calculates 1.0 / 3.0 as 0.333333333333333315, which is wrong for
FE_UPWARD (but correct for FE_NEAREST), and I imagine there are similar issues
for the other rounding modes (other than FE_NEAREST). Any thoughts as to what
could be going on?
Regards,
James
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