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Fix i386 atanhl spurious underflows (bug 18049) [committed]
- From: Joseph Myers <joseph at codesourcery dot com>
- To: <libc-alpha at sourceware dot org>
- Date: Tue, 19 May 2015 23:07:23 +0000
- Subject: Fix i386 atanhl spurious underflows (bug 18049) [committed]
- Authentication-results: sourceware.org; auth=none
The i386 implementation of atanhl, for small arguments, does a
calculation that involves computing twice the square of the argument,
resulting in spurious underflows for some arguments. This patch fixes
this by just returning the argument when its exponent is below -32,
with underflow being forced as needed for subnormal arguments.
Tested for x86 and x86_64. Committed.
(auto-libm-test-out diffs omitted below.)
2015-05-19 Joseph Myers <joseph@codesourcery.com>
[BZ #18049]
* sysdeps/i386/fpu/e_atanhl.S (__ieee754_atanhl): For exponents
below -32, return the argument, with underflow if subnormal.
* math/auto-libm-test-in: Add more tests of atanh.
* math/auto-libm-test-out: Regenerated.
diff --git a/math/auto-libm-test-in b/math/auto-libm-test-in
index 6fe0ed7..9e55d91 100644
--- a/math/auto-libm-test-in
+++ b/math/auto-libm-test-in
@@ -368,6 +368,11 @@ atanh 0x1p-57
atanh 0x1p-58
atanh 0x1p-59
atanh 0x1p-100
+atanh -0x1p-100
+atanh 0x1p-600
+atanh -0x1p-600
+atanh 0x1p-10000
+atanh -0x1p-10000
atanh -0x6.e6c77p-20
atanh 0x3.2ca824p-4
atanh -0x1.cc1d66p-4
diff --git a/sysdeps/i386/fpu/e_atanhl.S b/sysdeps/i386/fpu/e_atanhl.S
index 88a9703..1ad6851 100644
--- a/sysdeps/i386/fpu/e_atanhl.S
+++ b/sysdeps/i386/fpu/e_atanhl.S
@@ -56,6 +56,16 @@ ENTRY(__ieee754_atanhl)
andl $0x7fff, %eax
cmpl $0x7fff, %eax
je 5f
+ cmpl $0x3fdf, %eax
+ jge 7f
+ // Exponent below -32; return x, with underflow if subnormal.
+ fldt 4(%esp)
+ cmpl $0, %eax
+ jne 8f
+ fld %st(0)
+ fmul %st(0)
+ fstp %st(0)
+8: ret
7:
#ifdef PIC
--
Joseph S. Myers
joseph@codesourcery.com