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authorJoseph Myers <joseph@codesourcery.com>2015-08-10 20:35:30 +0000
committerJoseph Myers <joseph@codesourcery.com>2015-08-10 20:35:30 +0000
commit7ee06ef15827f8f2582a94b1ceaad47eaf502744 (patch)
treea9708093ad2f011a6a92b76e7aab574b72593649 /sysdeps
parenteb32b0d40308166c4d8f6330cc2958cb1e545075 (diff)
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Fix ldbl-128ibm tanhl inaccuracy (bug 18790).
ldbl-128ibm tanhl uses a too-small threshold to decide when to return +/-1, resulting in large errors. This patch changes it to a more appropriate threshold (the requirement is for 2*exp(-2|x|) to be small in terms of ulps of 1). Tested for x86_64, x86 and powerpc. [BZ #18790] * sysdeps/ieee754/ldbl-128ibm/s_tanhl.c (__tanhl): Increase threshold for returning +/- 1. * math/auto-libm-test-in: Add more tests of tanh. * math/auto-libm-test-out: Regenerated. * sysdeps/i386/fpu/libm-test-ulps: Update.
Diffstat (limited to 'sysdeps')
-rw-r--r--sysdeps/i386/fpu/libm-test-ulps2
-rw-r--r--sysdeps/ieee754/ldbl-128ibm/s_tanhl.c10
2 files changed, 6 insertions, 6 deletions
diff --git a/sysdeps/i386/fpu/libm-test-ulps b/sysdeps/i386/fpu/libm-test-ulps
index eddb3dc990..dbc8f2f331 100644
--- a/sysdeps/i386/fpu/libm-test-ulps
+++ b/sysdeps/i386/fpu/libm-test-ulps
@@ -1924,7 +1924,7 @@ double: 1
float: 1
idouble: 1
ifloat: 1
-ildouble: 5
+ildouble: 7
ldouble: 4
Function: "tanh_towardzero":
diff --git a/sysdeps/ieee754/ldbl-128ibm/s_tanhl.c b/sysdeps/ieee754/ldbl-128ibm/s_tanhl.c
index c63e25345d..fe396e9bd3 100644
--- a/sysdeps/ieee754/ldbl-128ibm/s_tanhl.c
+++ b/sysdeps/ieee754/ldbl-128ibm/s_tanhl.c
@@ -29,9 +29,9 @@ static char rcsid[] = "$NetBSD: s_tanh.c,v 1.7 1995/05/10 20:48:22 jtc Exp $";
* 2**-57 < x <= 1 : tanh(x) := -----; t = expm1(-2x)
* t + 2
* 2
- * 1 <= x <= 22.0 : tanh(x) := 1- ----- ; t=expm1(2x)
+ * 1 <= x <= 40.0 : tanh(x) := 1- ----- ; t=expm1(2x)
* t + 2
- * 22.0 < x <= INF : tanh(x) := 1.
+ * 40.0 < x <= INF : tanh(x) := 1.
*
* Special cases:
* tanh(NaN) is NaN;
@@ -61,8 +61,8 @@ long double __tanhl(long double x)
else return one/x-one; /* tanh(NaN) = NaN */
}
- /* |x| < 22 */
- if (ix < 0x4036000000000000LL) { /* |x|<22 */
+ /* |x| < 40 */
+ if (ix < 0x4044000000000000LL) { /* |x|<40 */
if (ix == 0)
return x; /* x == +-0 */
if (ix<0x3c60000000000000LL) /* |x|<2**-57 */
@@ -74,7 +74,7 @@ long double __tanhl(long double x)
t = __expm1l(-two*fabsl(x));
z= -t/(t+two);
}
- /* |x| > 22, return +-1 */
+ /* |x| > 40, return +-1 */
} else {
z = one - tiny; /* raised inexact flag */
}