math: Fix asin and acos invalid exception

This works around a gcc issue where it const folds inf/inf into nan,
preventing the invalid exception signal to be raised.

(x-x)/(x-x) is more robust against optimizations and works for x==nan
too.

The issue should be fixed in gcc-11.3.0 and gcc-12, but glibc supports
older compilers.

diff --git a/sysdeps/ieee754/dbl-64/e_asin.c b/sysdeps/ieee754/dbl-64/e_asin.c
index e7ea0cbe8fa35edcb5cc0e0e0d92169837d13c02..6b7c971e760747b2401617e91028728678a5aa85 100644 (file)
--- 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)