From 672f05a903f2b3ef7144c8c92efdff5e766a0dba Mon Sep 17 00:00:00 2001
From: XingLi <lixing@loongson.cn>
Date: Thu, 2 Feb 2023 18:49:01 +0800
Subject: [PATCH]    math: Fix asin and acos invalid exception with old gcc

    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.

    Reviewed-by: Wilco Dijkstra  <Wilco.Dijkstra@arm.com>

    upstream commit 7363a9a9a097c455a7ddb9386b4c6f7bdf91065f
    Author: Szabolcs Nagy <szabolcs.nagy@arm.com>
---
 sysdeps/ieee754/dbl-64/e_asin.c | 20 +++-----------------
 1 file changed, 3 insertions(+), 17 deletions(-)

diff --git a/sysdeps/ieee754/dbl-64/e_asin.c b/sysdeps/ieee754/dbl-64/e_asin.c
index 4473ae5d..b03a0a94 100644
--- a/sysdeps/ieee754/dbl-64/e_asin.c
+++ b/sysdeps/ieee754/dbl-64/e_asin.c
@@ -165,15 +165,8 @@ __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)
 #endif
@@ -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)
-- 
2.33.0

