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authorJoseph Myers <joseph@codesourcery.com>2015-02-26 21:06:34 +0000
committerJoseph Myers <joseph@codesourcery.com>2015-02-26 21:06:34 +0000
commit1d9ab20c14211abbf45514e63c190dfeec27fa5e (patch)
treecbe705e320799863f477d32c3062f6260c0c72a2 /sysdeps/ieee754
parentec0ce0d3be4ae21add09139c705852ed8bb114c7 (diff)
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Fix ldbl-128/ldbl-128ibm acosl inaccuracy (bug 18038, bug 18039).
The ldbl-128 and ldbl-128ibm implementations of acosl have similar
bugs, using a threshold of 0x1p-57L to determine when they just return
pi/2.  Since the result pi/2 - asinl (x) is roughly pi/2 - x for small
x, the relevant cut-off is actually x being < 0.5ulp of 1.  This patch
fixes the implementations to use that cut-off and adds tests of small
acos arguments.

Tested for powerpc and mips64.  Also tested for x86_64 and x86; no
ulps updates needed.

	[BZ #18038]
	[BZ #18039]
	* sysdeps/ieee754/ldbl-128/e_acosl.c (__ieee754_acosl): Only
	return pi/2 for arguments below 0x1p-113L.
	* sysdeps/ieee754/ldbl-128ibm/e_acosl.c (__ieee754_acosl): Only
	return pi/2 for arguments below 0x1p-106L.
	* math/auto-libm-test-in: Add more tests of acos.
	* math/auto-libm-test-out: Regenerated.
Diffstat (limited to 'sysdeps/ieee754')
-rw-r--r--sysdeps/ieee754/ldbl-128/e_acosl.c2
-rw-r--r--sysdeps/ieee754/ldbl-128ibm/e_acosl.c2
2 files changed, 2 insertions, 2 deletions
diff --git a/sysdeps/ieee754/ldbl-128/e_acosl.c b/sysdeps/ieee754/ldbl-128/e_acosl.c
index 28c94ed404..8c8ec93339 100644
--- a/sysdeps/ieee754/ldbl-128/e_acosl.c
+++ b/sysdeps/ieee754/ldbl-128/e_acosl.c
@@ -173,7 +173,7 @@ __ieee754_acosl (long double x)
     }
   else if (ix < 0x3ffe0000)	/* |x| < 0.5 */
     {
-      if (ix < 0x3fc60000)	/* |x| < 2**-57 */
+      if (ix < 0x3f8e0000)	/* |x| < 2**-113 */
 	return pio2_hi + pio2_lo;
       if (ix < 0x3ffde000)	/* |x| < .4375 */
 	{
diff --git a/sysdeps/ieee754/ldbl-128ibm/e_acosl.c b/sysdeps/ieee754/ldbl-128ibm/e_acosl.c
index 2cb288238b..e5030f1b52 100644
--- a/sysdeps/ieee754/ldbl-128ibm/e_acosl.c
+++ b/sysdeps/ieee754/ldbl-128ibm/e_acosl.c
@@ -169,7 +169,7 @@ __ieee754_acosl (long double x)
     }
   if (a < 0.5L)
     {
-      if (a < 6.938893903907228e-18L)	/* |x| < 2**-57 */
+      if (a < 0x1p-106L)
 	return pio2_hi + pio2_lo;
       if (a < 0.4375L)
 	{