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Fix i386 exp missing underflows (bug 18961) [committed]
- From: Joseph Myers <joseph at codesourcery dot com>
- To: <libc-alpha at sourceware dot org>
- Date: Mon, 14 Sep 2015 22:41:26 +0000
- Subject: Fix i386 exp missing underflows (bug 18961) [committed]
- Authentication-results: sourceware.org; auth=none
On i386, the double version of exp can miss underflow exceptions if
the result is in the subnormal range for double but the last 11 bits
of the 64-bit extended-precision mantissa happen to be zero. This
patch forces the exception in a similar way to previous fixes.
As with the exp2 fixes, the expf changes may in fact not be needed to
ensure underflow exceptions, but are included for consistency and to
fix the exp part of bug 18875 by ensuring that excess range and
precision is removed from underflowing return values.
Tested for x86_64 and x86. Committed.
(auto-libm-test-out diffs omitted below.)
2015-09-14 Joseph Myers <joseph@codesourcery.com>
[BZ #18875]
[BZ #18961]
* sysdeps/i386/fpu/e_exp.S (dbl_min): New object.
(MO): New macro.
(__ieee754_exp): For small results, force underflow exception and
remove excess range and precision from return value.
(__exp_finite): Likewise.
* sysdeps/i386/fpu/e_expf.S (flt_min): New object.
(MO): New macro.
(__ieee754_expf): For small results, force underflow exception and
remove excess range and precision from return value.
(__expf_finite): Likewise.
* math/auto-libm-test-in: Add more tests of exp.
* math/auto-libm-test-out: Regenerated.
diff --git a/math/auto-libm-test-in b/math/auto-libm-test-in
index 15c9146..9da01fb 100644
--- a/math/auto-libm-test-in
+++ b/math/auto-libm-test-in
@@ -1396,6 +1396,17 @@ exp -0x1.75f113c30b1c8p+9
exp -max
exp -11342.8125
exp -0x2.c5b2319c4843acc0p12
+exp -0x2.c469d9p+8
+exp -0x2.c46d96p+8
+exp -0x2.c46727p+8
+exp -0x2.c469dep+8
+exp -0x2.c46c04p+8
+exp -0x2.c46adep+8
+exp -0x2.c471b3p+8
+exp -0x2.c46993p+8
+exp -0x2.c49fap+8
+exp -0x2.c4ac1p+8
+exp -0x2.c4d89p+8
exp 0x1p-10
exp -0x1p-10
exp 0x1p-20
diff --git a/sysdeps/i386/fpu/e_exp.S b/sysdeps/i386/fpu/e_exp.S
index 2c331d9..c00beed 100644
--- a/sysdeps/i386/fpu/e_exp.S
+++ b/sysdeps/i386/fpu/e_exp.S
@@ -5,9 +5,25 @@
#include <machine/asm.h>
+ .section .rodata.cst8,"aM",@progbits,8
+ .p2align 3
+ .type dbl_min,@object
+dbl_min: .byte 0, 0, 0, 0, 0, 0, 0x10, 0
+ ASM_SIZE_DIRECTIVE(dbl_min)
+
+#ifdef PIC
+# define MO(op) op##@GOTOFF(%ecx)
+#else
+# define MO(op) op
+#endif
+
+ .text
/* e^x = 2^(x * log2(e)) */
ENTRY(__ieee754_exp)
+#ifdef PIC
+ LOAD_PIC_REG (cx)
+#endif
fldl 4(%esp)
/* I added the following ugly construct because exp(+-Inf) resulted
in NaN. The ugliness results from the bright minds at Intel.
@@ -30,7 +46,22 @@ ENTRY(__ieee754_exp)
faddp /* 2^(fract(x * log2(e))) */
fscale /* e^x */
fstp %st(1)
- ret
+ fldl MO(dbl_min)
+ fld %st(1)
+ fucompp
+ fnstsw
+ sahf
+ jnc 3f
+ subl $8, %esp
+ cfi_adjust_cfa_offset (8)
+ fld %st(0)
+ fmul %st(0)
+ fstpl (%esp)
+ fstpl (%esp)
+ fldl (%esp)
+ addl $8, %esp
+ cfi_adjust_cfa_offset (-8)
+3: ret
1: testl $0x200, %eax /* Test sign. */
jz 2f /* If positive, jump. */
@@ -41,6 +72,9 @@ END (__ieee754_exp)
ENTRY(__exp_finite)
+#ifdef PIC
+ LOAD_PIC_REG (cx)
+#endif
fldl2e
fmull 4(%esp) /* x * log2(e) */
fld %st
@@ -52,5 +86,20 @@ ENTRY(__exp_finite)
faddp /* 2^(fract(x * log2(e))) */
fscale /* e^x */
fstp %st(1)
- ret
+ fldl MO(dbl_min)
+ fld %st(1)
+ fucompp
+ fnstsw
+ sahf
+ jnc 4f
+ subl $8, %esp
+ cfi_adjust_cfa_offset (8)
+ fld %st(0)
+ fmul %st(0)
+ fstpl (%esp)
+ fstpl (%esp)
+ fldl (%esp)
+ addl $8, %esp
+ cfi_adjust_cfa_offset (-8)
+4: ret
END(__exp_finite)
diff --git a/sysdeps/i386/fpu/e_expf.S b/sysdeps/i386/fpu/e_expf.S
index 4e4f6a0..306afd1 100644
--- a/sysdeps/i386/fpu/e_expf.S
+++ b/sysdeps/i386/fpu/e_expf.S
@@ -6,9 +6,25 @@
#include <machine/asm.h>
+ .section .rodata.cst4,"aM",@progbits,4
+ .p2align 2
+ .type flt_min,@object
+flt_min: .byte 0, 0, 0x80, 0
+ ASM_SIZE_DIRECTIVE(flt_min)
+
+#ifdef PIC
+# define MO(op) op##@GOTOFF(%ecx)
+#else
+# define MO(op) op
+#endif
+
+ .text
/* e^x = 2^(x * log2(e)) */
ENTRY(__ieee754_expf)
+#ifdef PIC
+ LOAD_PIC_REG (cx)
+#endif
flds 4(%esp)
/* I added the following ugly construct because exp(+-Inf) resulted
in NaN. The ugliness results from the bright minds at Intel.
@@ -31,7 +47,22 @@ ENTRY(__ieee754_expf)
faddp /* 2^(fract(x * log2(e))) */
fscale /* e^x */
fstp %st(1)
- ret
+ flds MO(flt_min)
+ fld %st(1)
+ fucompp
+ fnstsw
+ sahf
+ jnc 3f
+ subl $4, %esp
+ cfi_adjust_cfa_offset (4)
+ fld %st(0)
+ fmul %st(0)
+ fstps (%esp)
+ fstps (%esp)
+ flds (%esp)
+ addl $4, %esp
+ cfi_adjust_cfa_offset (-4)
+3: ret
1: testl $0x200, %eax /* Test sign. */
jz 2f /* If positive, jump. */
@@ -42,6 +73,9 @@ END (__ieee754_expf)
ENTRY(__expf_finite)
+#ifdef PIC
+ LOAD_PIC_REG (cx)
+#endif
fldl2e
fmuls 4(%esp) /* x * log2(e) */
fld %st
@@ -53,5 +87,20 @@ ENTRY(__expf_finite)
faddp /* 2^(fract(x * log2(e))) */
fscale /* e^x */
fstp %st(1)
- ret
+ flds MO(flt_min)
+ fld %st(1)
+ fucompp
+ fnstsw
+ sahf
+ jnc 4f
+ subl $4, %esp
+ cfi_adjust_cfa_offset (4)
+ fld %st(0)
+ fmul %st(0)
+ fstps (%esp)
+ fstps (%esp)
+ flds (%esp)
+ addl $4, %esp
+ cfi_adjust_cfa_offset (-4)
+4: ret
END(__expf_finite)
--
Joseph S. Myers
joseph@codesourcery.com