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Fix log10 (1) in round-downward mode (bug 16977)
- From: "Joseph S. Myers" <joseph at codesourcery dot com>
- To: <libc-alpha at sourceware dot org>
- Date: Fri, 23 May 2014 00:55:20 +0000
- Subject: Fix log10 (1) in round-downward mode (bug 16977)
- Authentication-results: sourceware.org; auth=none
As with various other issues of this kind, bug 16977 is log10 (1)
wrongly returning -0 rather than +0 in round-downward mode because of
an implementation effectively in terms of log1p (x - 1). This patch
fixes the issue in the same way used for log.
Tested x86_64 and x86 and ulps updated accordingly. Also tested for
mips64 to confirm a fix was needed for ldbl-128 and to validate that
fix (also applied to ldbl-128ibm since that version of logl is
essentially the same as the ldbl-128 one).
2014-05-22 Joseph Myers <joseph@codesourcery.com>
[BZ #16977]
* sysdeps/i386/fpu/e_log10.S (__ieee754_log10): Take absolute
value when x - 1 is zero.
* sysdeps/i386/fpu/e_log10f.S (__ieee754_log10f): Likewise.
* sysdeps/i386/fpu/e_log10l.S (__ieee754_log10l): Likewise.
* sysdeps/ieee754/ldbl-128/e_log10l.c (__ieee754_log10l): Return
0.0L for an argument of 1.0L.
* sysdeps/ieee754/ldbl-128ibm/e_log10l.c (__ieee754_log10l):
Likewise.
* sysdeps/x86_64/fpu/e_log10l.S (__ieee754_log10l): Take absolute
value when x - 1 is zero.
* math/libm-test.inc (log10_test): Use ALL_RM_TEST.
* sysdeps/i386/fpu/libm-test-ulps: Update.
* sysdeps/x86_64/fpu/libm-test-ulps: Likewise.
diff --git a/math/libm-test.inc b/math/libm-test.inc
index de7bc8a..0d467a2 100644
--- a/math/libm-test.inc
+++ b/math/libm-test.inc
@@ -7798,9 +7798,7 @@ static const struct test_f_f_data log10_test_data[] =
static void
log10_test (void)
{
- START (log10, 0);
- RUN_TEST_LOOP_f_f (log10, log10_test_data, );
- END;
+ ALL_RM_TEST (log10, 0, log10_test_data, RUN_TEST_LOOP_f_f, END);
}
diff --git a/sysdeps/i386/fpu/e_log10.S b/sysdeps/i386/fpu/e_log10.S
index ce6a81a..1727708 100644
--- a/sysdeps/i386/fpu/e_log10.S
+++ b/sysdeps/i386/fpu/e_log10.S
@@ -46,7 +46,13 @@ ENTRY(__ieee754_log10)
fnstsw // x-1 : x : log10(2)
andb $0x45, %ah
jz 2f
- fstp %st(1) // x-1 : log10(2)
+ fxam
+ fnstsw
+ andb $0x45, %ah
+ cmpb $0x40, %ah
+ jne 5f
+ fabs // log10(1) is +0 in all rounding modes.
+5: fstp %st(1) // x-1 : log10(2)
fyl2xp1 // log10(x)
ret
diff --git a/sysdeps/i386/fpu/e_log10f.S b/sysdeps/i386/fpu/e_log10f.S
index 8c20723..72a3b88 100644
--- a/sysdeps/i386/fpu/e_log10f.S
+++ b/sysdeps/i386/fpu/e_log10f.S
@@ -47,7 +47,13 @@ ENTRY(__ieee754_log10f)
fnstsw // x-1 : x : log10(2)
andb $0x45, %ah
jz 2f
- fstp %st(1) // x-1 : log10(2)
+ fxam
+ fnstsw
+ andb $0x45, %ah
+ cmpb $0x40, %ah
+ jne 5f
+ fabs // log10(1) is +0 in all rounding modes.
+5: fstp %st(1) // x-1 : log10(2)
fyl2xp1 // log10(x)
ret
diff --git a/sysdeps/i386/fpu/e_log10l.S b/sysdeps/i386/fpu/e_log10l.S
index cde987b..45b9c6d 100644
--- a/sysdeps/i386/fpu/e_log10l.S
+++ b/sysdeps/i386/fpu/e_log10l.S
@@ -48,7 +48,13 @@ ENTRY(__ieee754_log10l)
fnstsw // x-1 : x : log10(2)
andb $0x45, %ah
jz 2f
- fstp %st(1) // x-1 : log10(2)
+ fxam
+ fnstsw
+ andb $0x45, %ah
+ cmpb $0x40, %ah
+ jne 5f
+ fabs // log10(1) is +0 in all rounding modes.
+5: fstp %st(1) // x-1 : log10(2)
fyl2xp1 // log10(x)
ret
diff --git a/sysdeps/i386/fpu/libm-test-ulps b/sysdeps/i386/fpu/libm-test-ulps
index 946cad4..1e89284 100644
--- a/sysdeps/i386/fpu/libm-test-ulps
+++ b/sysdeps/i386/fpu/libm-test-ulps
@@ -1536,6 +1536,30 @@ Function: "log10":
ildouble: 1
ldouble: 1
+Function: "log10_downward":
+double: 1
+float: 1
+idouble: 1
+ifloat: 1
+ildouble: 1
+ldouble: 1
+
+Function: "log10_towardzero":
+double: 1
+float: 1
+idouble: 1
+ifloat: 1
+ildouble: 1
+ldouble: 1
+
+Function: "log10_upward":
+double: 1
+float: 1
+idouble: 1
+ifloat: 1
+ildouble: 1
+ldouble: 1
+
Function: "log1p":
ildouble: 1
ldouble: 1
diff --git a/sysdeps/ieee754/ldbl-128/e_log10l.c b/sysdeps/ieee754/ldbl-128/e_log10l.c
index b403f81..618255f 100644
--- a/sysdeps/ieee754/ldbl-128/e_log10l.c
+++ b/sysdeps/ieee754/ldbl-128/e_log10l.c
@@ -193,6 +193,9 @@ __ieee754_log10l (long double x)
if (hx >= 0x7fff000000000000LL)
return (x + x);
+ if (x == 1.0L)
+ return 0.0L;
+
/* separate mantissa from exponent */
/* Note, frexp is used so that denormal numbers
diff --git a/sysdeps/ieee754/ldbl-128ibm/e_log10l.c b/sysdeps/ieee754/ldbl-128ibm/e_log10l.c
index 1a6a4a0..7477791 100644
--- a/sysdeps/ieee754/ldbl-128ibm/e_log10l.c
+++ b/sysdeps/ieee754/ldbl-128ibm/e_log10l.c
@@ -195,6 +195,9 @@ __ieee754_log10l (long double x)
if (hx >= 0x7ff0000000000000LL)
return (x + x);
+ if (x == 1.0L)
+ return 0.0L;
+
/* separate mantissa from exponent */
/* Note, frexp is used so that denormal numbers
diff --git a/sysdeps/x86_64/fpu/e_log10l.S b/sysdeps/x86_64/fpu/e_log10l.S
index 6c07024..2607ad1 100644
--- a/sysdeps/x86_64/fpu/e_log10l.S
+++ b/sysdeps/x86_64/fpu/e_log10l.S
@@ -46,7 +46,13 @@ ENTRY(__ieee754_log10l)
fnstsw // x-1 : x : log10(2)
andb $0x45, %ah
jz 2f
- fstp %st(1) // x-1 : log10(2)
+ fxam
+ fnstsw
+ andb $0x45, %ah
+ cmpb $0x40, %ah
+ jne 5f
+ fabs // log10(1) is +0 in all rounding modes.
+5: fstp %st(1) // x-1 : log10(2)
fyl2xp1 // log10(x)
ret
diff --git a/sysdeps/x86_64/fpu/libm-test-ulps b/sysdeps/x86_64/fpu/libm-test-ulps
index d472876..bb549d2 100644
--- a/sysdeps/x86_64/fpu/libm-test-ulps
+++ b/sysdeps/x86_64/fpu/libm-test-ulps
@@ -1611,6 +1611,30 @@ ifloat: 2
ildouble: 1
ldouble: 1
+Function: "log10_downward":
+double: 1
+float: 1
+idouble: 1
+ifloat: 1
+ildouble: 1
+ldouble: 1
+
+Function: "log10_towardzero":
+double: 1
+float: 1
+idouble: 1
+ifloat: 1
+ildouble: 1
+ldouble: 1
+
+Function: "log10_upward":
+double: 1
+float: 1
+idouble: 1
+ifloat: 1
+ildouble: 1
+ldouble: 1
+
Function: "log1p":
float: 1
ifloat: 1
--
Joseph S. Myers
joseph@codesourcery.com