On 3/15/21 3:10 AM, Philippe Mathieu-Daudé wrote:
On 3/15/21 12:48 AM, Richard Henderson wrote:
Use fma to simulatneously scale and round up fraction.
"simultaneously"
The libm function will always return a properly rounded double precision
value, which will eliminate any extra precision the x87 co-processor may
give us, which will keep the output predictable vs other hosts.
Adding DBL_EPSILON while scaling should help with fractions like
12.345, where the closest representable number is actually 12.3449*.
Signed-off-by: Richard Henderson <richard.hender...@linaro.org>
---
util/cutils.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/util/cutils.c b/util/cutils.c
index d89a40a8c3..f7f8e48a68 100644
--- a/util/cutils.c
+++ b/util/cutils.c
@@ -342,7 +342,7 @@ static int do_strtosz(const char *nptr, const char **end,
if (val > (UINT64_MAX - ((uint64_t) (fraction * mul))) / mul) {
Shouldn't we use fma() here too? ^^^^^^^^^^^^^^^^^^^^^^^^^^
Yep, I should have looked at the larger context.
r~
retval = -ERANGE;
goto out;
}
- *result = val * mul + (uint64_t) (fraction * mul);
+ *result = val * mul + (uint64_t)fma(fraction, mul, DBL_EPSILON);
retval = 0;
out:
