* [PATCH] math: Fix asin and acos invalid exception with old gcc
@ 2022-10-14 14:31 Wilco Dijkstra
0 siblings, 0 replies; 2+ messages in thread
From: Wilco Dijkstra @ 2022-10-14 14:31 UTC (permalink / raw)
To: Szabolcs Nagy; +Cc: 'GNU C Library'
Hi Szabolcs,
> This works around a gcc issue where it const folded inf/inf into nan,
> preventing the invalid exception to be signalled.
>
> (x-x)/(x-x) is more robust against optimizations and works for all
> out of bounds values including x==nan.
>
> The gcc issue https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95115
> should be fixed on release branches starting from gcc-10, but it is
> better to change the code in case glibc is built with older gcc.
LGTM.
Reviewed-by: Wilco Dijkstra <Wilco.Dijkstra@arm.com>
Cheers,
Wilco
---
sysdeps/ieee754/dbl-64/e_asin.c | 18 ++----------------
1 file changed, 2 insertions(+), 16 deletions(-)
diff --git a/sysdeps/ieee754/dbl-64/e_asin.c b/sysdeps/ieee754/dbl-64/e_asin.c
index e7ea0cbe8f..6b7c971e76 100644
--- a/sysdeps/ieee754/dbl-64/e_asin.c
+++ b/sysdeps/ieee754/dbl-64/e_asin.c
@@ -165,14 +165,7 @@ __ieee754_asin(double x){
/*---------------------------- |x|>=1 -------------------------------*/
else if (k==0x3ff00000 && u.i[LOW_HALF]==0) return (m>0)?hp0.x:-hp0.x;
else
- if (k>0x7ff00000 || (k == 0x7ff00000 && u.i[LOW_HALF] != 0)) return x + x;
- else {
- u.i[HIGH_HALF]=0x7ff00000;
- v.i[HIGH_HALF]=0x7ff00000;
- u.i[LOW_HALF]=0;
- v.i[LOW_HALF]=0;
- return u.x/v.x; /* NaN */
- }
+ return (x - x) / (x - x);
}
#ifndef __ieee754_asin
libm_alias_finite (__ieee754_asin, __asin)
@@ -334,14 +327,7 @@ __ieee754_acos(double x)
else
if (k==0x3ff00000 && u.i[LOW_HALF]==0) return (m>0)?0:2.0*hp0.x;
else
- if (k>0x7ff00000 || (k == 0x7ff00000 && u.i[LOW_HALF] != 0)) return x + x;
- else {
- u.i[HIGH_HALF]=0x7ff00000;
- v.i[HIGH_HALF]=0x7ff00000;
- u.i[LOW_HALF]=0;
- v.i[LOW_HALF]=0;
- return u.x/v.x;
- }
+ return (x - x) / (x - x);
}
#ifndef __ieee754_acos
libm_alias_finite (__ieee754_acos, __acos)
^ permalink raw reply [flat|nested] 2+ messages in thread
* [PATCH] math: Fix asin and acos invalid exception with old gcc
@ 2022-10-14 12:41 Szabolcs Nagy
0 siblings, 0 replies; 2+ messages in thread
From: Szabolcs Nagy @ 2022-10-14 12:41 UTC (permalink / raw)
To: libc-alpha; +Cc: Yu-Chien Peter Lin
This works around a gcc issue where it const folded inf/inf into nan,
preventing the invalid exception to be signalled.
(x-x)/(x-x) is more robust against optimizations and works for all
out of bounds values including x==nan.
The gcc issue https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95115
should be fixed on release branches starting from gcc-10, but it is
better to change the code in case glibc is built with older gcc.
---
sysdeps/ieee754/dbl-64/e_asin.c | 18 ++----------------
1 file changed, 2 insertions(+), 16 deletions(-)
diff --git a/sysdeps/ieee754/dbl-64/e_asin.c b/sysdeps/ieee754/dbl-64/e_asin.c
index e7ea0cbe8f..6b7c971e76 100644
--- a/sysdeps/ieee754/dbl-64/e_asin.c
+++ b/sysdeps/ieee754/dbl-64/e_asin.c
@@ -165,14 +165,7 @@ __ieee754_asin(double x){
/*---------------------------- |x|>=1 -------------------------------*/
else if (k==0x3ff00000 && u.i[LOW_HALF]==0) return (m>0)?hp0.x:-hp0.x;
else
- if (k>0x7ff00000 || (k == 0x7ff00000 && u.i[LOW_HALF] != 0)) return x + x;
- else {
- u.i[HIGH_HALF]=0x7ff00000;
- v.i[HIGH_HALF]=0x7ff00000;
- u.i[LOW_HALF]=0;
- v.i[LOW_HALF]=0;
- return u.x/v.x; /* NaN */
- }
+ return (x - x) / (x - x);
}
#ifndef __ieee754_asin
libm_alias_finite (__ieee754_asin, __asin)
@@ -334,14 +327,7 @@ __ieee754_acos(double x)
else
if (k==0x3ff00000 && u.i[LOW_HALF]==0) return (m>0)?0:2.0*hp0.x;
else
- if (k>0x7ff00000 || (k == 0x7ff00000 && u.i[LOW_HALF] != 0)) return x + x;
- else {
- u.i[HIGH_HALF]=0x7ff00000;
- v.i[HIGH_HALF]=0x7ff00000;
- u.i[LOW_HALF]=0;
- v.i[LOW_HALF]=0;
- return u.x/v.x;
- }
+ return (x - x) / (x - x);
}
#ifndef __ieee754_acos
libm_alias_finite (__ieee754_acos, __acos)
--
2.25.1
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2022-10-14 12:41 Szabolcs Nagy
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