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Fix lgammaf spurious underflow (bug 15427)
- From: "Joseph S. Myers" <joseph at codesourcery dot com>
- To: <libc-alpha at sourceware dot org>
- Date: Mon, 2 Sep 2013 20:41:13 +0000
- Subject: Fix lgammaf spurious underflow (bug 15427)
- Authentication-results: sourceware.org; auth=none
This patch fixes bug 15427, spurious underflow exceptions from lgammaf
on arguments close to 0. The code uses 2**-70 as a threshold for
returning -log(|x|), but what's relevant there is that lgamma(1+x) (on
the order of constant*x) is negligible compared to -log(|x|); 2**-70
is a value chosen for double and a value such as 2**30 suffices for
float and also suffices to avoid underflow from the calculation of
polynomial approximations in terms of x.
Tested x86_64 and x86 and ulps updated accordingly.
2013-09-02 Joseph Myers <joseph@codesourcery.com>
[BZ #15427]
* sysdeps/ieee754/flt-32/e_lgammaf_r.c (__ieee754_lgammaf_r): Use
2**-30 instead of 2**-70 as threshold for returning -log(|x|).
* math/libm-test.inc (lgamma_test_data): Add more tests.
* 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 fb5e977..98a609a 100644
--- a/math/libm-test.inc
+++ b/math/libm-test.inc
@@ -9978,6 +9978,62 @@ static const struct test_f_f1_data lgamma_test_data[] =
TEST_f_f1 (lgamma, -0.5, M_LOG_2_SQRT_PIl, -1),
TEST_f_f1 (lgamma, 0.7L, 0.260867246531666514385732417016759578L, 1),
TEST_f_f1 (lgamma, 1.2L, -0.853740900033158497197028392998854470e-1L, 1),
+
+ TEST_f_f1 (lgamma, 0x1p-5L, 3.4484891277979584796832693452686366085801e+00L, 1),
+ TEST_f_f1 (lgamma, -0x1p-5L, 3.4845895751341394376217526729956836492792e+00L, -1),
+ TEST_f_f1 (lgamma, 0x1p-10L, 6.9309089024194618895406190646600805357273e+00L, 1),
+ TEST_f_f1 (lgamma, -0x1p-10L, 6.9320362775113082175565786721095494761582e+00L, -1),
+ TEST_f_f1 (lgamma, 0x1p-15L, 1.0397190093941001762077888432721419773538e+01L, 1),
+ TEST_f_f1 (lgamma, -0x1p-15L, 1.0397225324389321751118257981741350715545e+01L, -1),
+ TEST_f_f1 (lgamma, 0x1p-20L, 1.3862943060723899573457963336920089012399e+01L, 1),
+ TEST_f_f1 (lgamma, -0x1p-20L, 1.3862944161675408862049886226750366625112e+01L, -1),
+ TEST_f_f1 (lgamma, 0x1p-25L, 1.7328679496796266133304874243201700664713e+01L, 1),
+ TEST_f_f1 (lgamma, -0x1p-25L, 1.7328679531201000798551671833865469674673e+01L, -1),
+ TEST_f_f1 (lgamma, 0x1p-30L, 2.0794415416260785304085859198055798098863e+01L, 1),
+ TEST_f_f1 (lgamma, -0x1p-30L, 2.0794415417335933262374820960532606449975e+01L, -1),
+ TEST_f_f1 (lgamma, 0x1p-40L, 2.7725887222397287402100277256545578941303e+01L, 1),
+ TEST_f_f1 (lgamma, -0x1p-40L, 2.7725887222398337351278293820766115529596e+01L, -1),
+ TEST_f_f1 (lgamma, 0x1p-50L, 3.4657359027997264958191108994508978906983e+01L, 1),
+ TEST_f_f1 (lgamma, -0x1p-50L, 3.4657359027997265983532103151309975524744e+01L, -1),
+ TEST_f_f1 (lgamma, 0x1p-60L, 4.1588830833596718564533272505187468598519e+01L, 1),
+ TEST_f_f1 (lgamma, -0x1p-60L, 4.1588830833596718565534582069793719571779e+01L, -1),
+ TEST_f_f1 (lgamma, 0x1p-64L, 4.4361419555836499802671564849429355013920e+01L, 1),
+ TEST_f_f1 (lgamma, -0x1p-64L, 4.4361419555836499802734146697217245699749e+01L, -1),
+ TEST_f_f1 (lgamma, 0x1p-70L, 4.8520302639196171659205759581386516869302e+01L, 1),
+ TEST_f_f1 (lgamma, -0x1p-70L, 4.8520302639196171659206737422758202661268e+01L, -1),
+ TEST_f_f1 (lgamma, 0x1p-100L, 6.9314718055994530941723212145817201464678e+01L, 1),
+ TEST_f_f1 (lgamma, -0x1p-100L, 6.9314718055994530941723212145818112150422e+01L, -1),
+ TEST_f_f1 (lgamma, 0x1p-126L, 8.7336544750553108986571247303730247577506e+01L, 1),
+ TEST_f_f1 (lgamma, -0x1p-126L, 8.7336544750553108986571247303730247577520e+01L, -1),
+ TEST_f_f1 (lgamma, 0x1p-149L, 1.0327892990343185110316758609726830864325e+02L, 1),
+ TEST_f_f1 (lgamma, -0x1p-149L, 1.0327892990343185110316758609726830864325e+02L, -1),
+#ifndef TEST_FLOAT
+ TEST_f_f1 (lgamma, 0x1p-200L, 1.3862943611198906188344642429163531361510e+02L, 1),
+ TEST_f_f1 (lgamma, -0x1p-200L, 1.3862943611198906188344642429163531361510e+02L, -1),
+ TEST_f_f1 (lgamma, 0x1p-500L, 3.4657359027997265470861606072908828403775e+02L, 1),
+ TEST_f_f1 (lgamma, -0x1p-500L, 3.4657359027997265470861606072908828403775e+02L, -1),
+ TEST_f_f1 (lgamma, 0x1p-1000L, 6.9314718055994530941723212145817656807550e+02L, 1),
+ TEST_f_f1 (lgamma, -0x1p-1000L, 6.9314718055994530941723212145817656807550e+02L, -1),
+ TEST_f_f1 (lgamma, 0x1p-1022L, 7.0839641853226410622441122813025645257316e+02L, 1),
+ TEST_f_f1 (lgamma, -0x1p-1022L, 7.0839641853226410622441122813025645257316e+02L, -1),
+ TEST_f_f1 (lgamma, 0x1p-1074L, 7.4444007192138126231410729844608163411309e+02L, 1),
+ TEST_f_f1 (lgamma, -0x1p-1074L, 7.4444007192138126231410729844608163411309e+02L, -1),
+#endif
+#if defined TEST_LDOUBLE && LDBL_MIN_EXP <= -16381
+ TEST_f_f1 (lgamma, 0x1p-5000L, 3.4657359027997265470861606072908828403775e+03L, 1),
+ TEST_f_f1 (lgamma, -0x1p-5000L, 3.4657359027997265470861606072908828403775e+03L, -1),
+ TEST_f_f1 (lgamma, 0x1p-10000L, 6.9314718055994530941723212145817656807550e+03L, 1),
+ TEST_f_f1 (lgamma, -0x1p-10000L, 6.9314718055994530941723212145817656807550e+03L, -1),
+ TEST_f_f1 (lgamma, 0x1p-16382L, 1.1355137111933024058873096613727848538213e+04L, 1),
+ TEST_f_f1 (lgamma, -0x1p-16382L, 1.1355137111933024058873096613727848538213e+04L, -1),
+ TEST_f_f1 (lgamma, 0x1p-16445L, 1.1398805384308300613366382237379713662002e+04L, 1),
+ TEST_f_f1 (lgamma, -0x1p-16445L, 1.1398805384308300613366382237379713662002e+04L, -1),
+# if LDBL_MANT_DIG >= 113
+ TEST_f_f1 (lgamma, 0x1p-16494L, 1.1432769596155737933527826611331164313837e+04L, 1),
+ TEST_f_f1 (lgamma, -0x1p-16494L, 1.1432769596155737933527826611331164313837e+04L, -1),
+# endif
+#endif
+
};
static void
diff --git a/sysdeps/i386/fpu/libm-test-ulps b/sysdeps/i386/fpu/libm-test-ulps
index 8244863..4759aa9 100644
--- a/sysdeps/i386/fpu/libm-test-ulps
+++ b/sysdeps/i386/fpu/libm-test-ulps
@@ -5470,9 +5470,35 @@ double: 1
idouble: 1
ildouble: 1
ldouble: 1
+Test "gamma (-0x1p-10)":
+double: 1
+float: 1
+idouble: 1
+ifloat: 1
+ildouble: 1
+ldouble: 1
+Test "gamma (-0x1p-15)":
+double: 1
+float: 1
+idouble: 1
+ifloat: 1
+Test "gamma (-0x1p-20)":
+double: 1
+idouble: 1
+Test "gamma (-0x1p-30)":
+double: 1
+idouble: 1
+ildouble: 1
+ldouble: 1
+Test "gamma (-0x1p-5)":
+double: 1
+idouble: 1
Test "gamma (0.7)":
float: 1
ifloat: 1
+Test "gamma (0x1p-40)":
+ildouble: 1
+ldouble: 1
Test "gamma (1.2)":
double: 1
float: 2
@@ -5723,9 +5749,35 @@ double: 1
idouble: 1
ildouble: 1
ldouble: 1
+Test "lgamma (-0x1p-10)":
+double: 1
+float: 1
+idouble: 1
+ifloat: 1
+ildouble: 1
+ldouble: 1
+Test "lgamma (-0x1p-15)":
+double: 1
+float: 1
+idouble: 1
+ifloat: 1
+Test "lgamma (-0x1p-20)":
+double: 1
+idouble: 1
+Test "lgamma (-0x1p-30)":
+double: 1
+idouble: 1
+ildouble: 1
+ldouble: 1
+Test "lgamma (-0x1p-5)":
+double: 1
+idouble: 1
Test "lgamma (0.7)":
float: 1
ifloat: 1
+Test "lgamma (0x1p-40)":
+ildouble: 1
+ldouble: 1
Test "lgamma (1.2)":
double: 1
float: 2
diff --git a/sysdeps/ieee754/flt-32/e_lgammaf_r.c b/sysdeps/ieee754/flt-32/e_lgammaf_r.c
index 2e92269..0dba9af 100644
--- a/sysdeps/ieee754/flt-32/e_lgammaf_r.c
+++ b/sysdeps/ieee754/flt-32/e_lgammaf_r.c
@@ -150,8 +150,8 @@ __ieee754_lgammaf_r(float x, int *signgamp)
*signgamp = -1;
return one/fabsf(x);
}
- if(__builtin_expect(ix<0x1c800000, 0)) {
- /* |x|<2**-70, return -log(|x|) */
+ if(__builtin_expect(ix<0x30800000, 0)) {
+ /* |x|<2**-30, return -log(|x|) */
if(hx<0) {
*signgamp = -1;
return -__ieee754_logf(-x);
diff --git a/sysdeps/x86_64/fpu/libm-test-ulps b/sysdeps/x86_64/fpu/libm-test-ulps
index 477eedc..6fbfa64 100644
--- a/sysdeps/x86_64/fpu/libm-test-ulps
+++ b/sysdeps/x86_64/fpu/libm-test-ulps
@@ -6222,11 +6222,39 @@ idouble: 1
Test "gamma (-0.5)":
ildouble: 1
ldouble: 1
+Test "gamma (-0x1p-10)":
+double: 1
+idouble: 1
+ildouble: 1
+ldouble: 1
+Test "gamma (-0x1p-15)":
+double: 1
+float: 1
+idouble: 1
+ifloat: 1
+Test "gamma (-0x1p-20)":
+double: 1
+idouble: 1
+Test "gamma (-0x1p-30)":
+ildouble: 1
+ldouble: 1
+Test "gamma (-0x1p-5)":
+double: 1
+idouble: 1
Test "gamma (0.7)":
double: 1
float: 1
idouble: 1
ifloat: 1
+Test "gamma (0x1p-10)":
+float: 1
+ifloat: 1
+Test "gamma (0x1p-30)":
+double: 1
+idouble: 1
+Test "gamma (0x1p-40)":
+ildouble: 1
+ldouble: 1
Test "gamma (1.2)":
double: 1
float: 2
@@ -6491,11 +6519,39 @@ ldouble: 2
Test "lgamma (-0.5)":
ildouble: 1
ldouble: 1
+Test "lgamma (-0x1p-10)":
+double: 1
+idouble: 1
+ildouble: 1
+ldouble: 1
+Test "lgamma (-0x1p-15)":
+double: 1
+float: 1
+idouble: 1
+ifloat: 1
+Test "lgamma (-0x1p-20)":
+double: 1
+idouble: 1
+Test "lgamma (-0x1p-30)":
+ildouble: 1
+ldouble: 1
+Test "lgamma (-0x1p-5)":
+double: 1
+idouble: 1
Test "lgamma (0.7)":
double: 1
float: 1
idouble: 1
ifloat: 1
+Test "lgamma (0x1p-10)":
+float: 1
+ifloat: 1
+Test "lgamma (0x1p-30)":
+double: 1
+idouble: 1
+Test "lgamma (0x1p-40)":
+ildouble: 1
+ldouble: 1
Test "lgamma (1.2)":
double: 1
float: 2
--
Joseph S. Myers
joseph@codesourcery.com