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Fix x86 / x86_64 expl, exp10l missing underflows (bug 16361) [committed]
- From: Joseph Myers <joseph at codesourcery dot com>
- To: <libc-alpha at sourceware dot org>
- Date: Sun, 21 Jun 2015 17:48:32 +0000
- Subject: Fix x86 / x86_64 expl, exp10l missing underflows (bug 16361) [committed]
- Authentication-results: sourceware.org; auth=none
Similar to various other bugs in this area, the x86 and x86_64
implementations of expl / exp10l can fail to produce underflow
exceptions when the unscaled result has trailing 0 bits so the scaling
down to subnormal precision is exact. This patch fixes this by
forcing the exception in the case of tiny results.
Tested for x86_64 and x86. Committed.
(auto-libm-test-out diffs omitted below.)
2015-06-21 Joseph Myers <joseph@codesourcery.com>
[BZ #16361]
* sysdeps/i386/fpu/e_expl.S [!USE_AS_EXPM1L] (cmin): New object.
[!USE_AS_EXPM1L] (IEEE754_EXPL): Force underflow exception for
tiny results.
* sysdeps/x86_64/fpu/e_expl.S [!USE_AS_EXPM1L] (cmin): New object.
[!USE_AS_EXPM1L] (IEEE754_EXPL): Force underflow exception for
tiny results.
* math/auto-libm-test-in: Add more tests of exp and exp10. Do not
mark underflow exceptions as possibly missing for bug 16361.
* math/auto-libm-test-out: Regenerated.
diff --git a/math/auto-libm-test-in b/math/auto-libm-test-in
index 6ec4bc6..e8e4da6 100644
--- a/math/auto-libm-test-in
+++ b/math/auto-libm-test-in
@@ -1191,6 +1191,7 @@ exp -7.4444006192138124e+02
exp -0x1.75f113c30b1c8p+9
exp -max
exp -11342.8125
+exp -0x2.c5b2319c4843acc0p12
exp 0x1p-10
exp -0x1p-10
exp 0x1p-20
@@ -1223,8 +1224,8 @@ exp10 305
exp10 -305
# GCC bug 59666: results on directed rounding may be incorrect.
exp10 4932 xfail-rounding:ldbl-128ibm
-# Bug 16361: underflow exception may be misssing
-exp10 -4932 missing-underflow:ldbl-96-intel:x86 missing-underflow:ldbl-96-intel:x86_64
+exp10 -4932
+exp10 -0x1.343793004f503232p12
# GCC bug 59666: results on directed rounding may be incorrect.
exp10 1e5 xfail-rounding:ldbl-128ibm
exp10 -1e5
diff --git a/sysdeps/i386/fpu/e_expl.S b/sysdeps/i386/fpu/e_expl.S
index c7e4373..74968bb 100644
--- a/sysdeps/i386/fpu/e_expl.S
+++ b/sysdeps/i386/fpu/e_expl.S
@@ -65,6 +65,10 @@ c1: .byte 0x20, 0xfa, 0xee, 0xc2, 0x5f, 0x70, 0xa5, 0xec, 0xed, 0x3f
csat: .byte 0, 0, 0, 0, 0, 0, 0, 0x80, 0x0e, 0x40
.byte 0, 0, 0, 0, 0, 0
ASM_SIZE_DIRECTIVE(csat)
+ .type cmin,@object
+cmin: .byte 0, 0, 0, 0, 0, 0, 0, 0x80, 0x1, 0
+ .byte 0, 0, 0, 0, 0, 0
+ ASM_SIZE_DIRECTIVE(cmin)
#endif
#ifdef PIC
@@ -189,8 +193,18 @@ ENTRY(IEEE754_EXPL)
fstp %st(1) /* 2 */
fscale /* 2 scale factor is st(1); base^x */
fstp %st(1) /* 1 */
+ /* Ensure underflow for tiny result. */
+ fldt MO(cmin) /* 2 cmin */
+ fld %st(1) /* 3 */
+ fcompp /* 1 */
+ fnstsw
+ sahf
+ jnc 6f
+ fld %st
+ fmul %st
+ fstp %st
#endif
- fstp %st(1) /* 0 */
+6: fstp %st(1) /* 0 */
jmp 2f
1:
#ifdef USE_AS_EXPM1L
diff --git a/sysdeps/x86_64/fpu/e_expl.S b/sysdeps/x86_64/fpu/e_expl.S
index 0ebe388..866bad2 100644
--- a/sysdeps/x86_64/fpu/e_expl.S
+++ b/sysdeps/x86_64/fpu/e_expl.S
@@ -65,6 +65,10 @@ c1: .byte 0x20, 0xfa, 0xee, 0xc2, 0x5f, 0x70, 0xa5, 0xec, 0xed, 0x3f
csat: .byte 0, 0, 0, 0, 0, 0, 0, 0x80, 0x0e, 0x40
.byte 0, 0, 0, 0, 0, 0
ASM_SIZE_DIRECTIVE(csat)
+ .type cmin,@object
+cmin: .byte 0, 0, 0, 0, 0, 0, 0, 0x80, 0x1, 0
+ .byte 0, 0, 0, 0, 0, 0
+ ASM_SIZE_DIRECTIVE(cmin)
#endif
#ifdef PIC
@@ -182,8 +186,17 @@ ENTRY(IEEE754_EXPL)
fstp %st(1) /* 2 */
fscale /* 2 scale factor is st(1); base^x */
fstp %st(1) /* 1 */
+ /* Ensure underflow for tiny result. */
+ fldt MO(cmin) /* 2 cmin */
+ fld %st(1) /* 3 */
+ fcomip %st(1), %st /* 2 */
+ fstp %st /* 1 */
+ jnc 6f
+ fld %st
+ fmul %st
+ fstp %st
#endif
- fstp %st(1) /* 0 */
+6: fstp %st(1) /* 0 */
jmp 2f
1:
#ifdef USE_AS_EXPM1L
--
Joseph S. Myers
joseph@codesourcery.com