From 4ba7a00fe3779e6ffafad6d47305b3491cdac33e Mon Sep 17 00:00:00 2001 From: Joseph Myers Date: Wed, 18 Jun 2014 12:32:01 +0000 Subject: [PATCH] Fix __ieee754_logl (-LDBL_MAX) in FE_DOWNWARD mode (bug 17022). This patch fixes __ieee754_logl (-LDBL_MAX) on x86_64 and x86 not to subtract 1 from its argument and so cause spurious overflow in FE_DOWNWARD mode. (For any argument strictly less than -1, it doesn't matter whether or not 1 is subtracted before computing log1p, as long as the result doesn't overflow to -Inf.) Tested x86_64 and x86. (This particular case lacks test coverage, since the testsuite doesn't cover -lieee, but it will be covered by tests after the following patch to test pow in all rounding modes, which was the context in which this bug was found.) [BZ #17022] * sysdeps/i386/fpu/e_logl.S (__ieee754_logl): Do not subtract 1 from arguments -2 or below. * sysdeps/i386/i686/fpu/e_logl.S (__ieee754_logl): Likewise. * sysdeps/x86_64/fpu/e_logl.S (__ieee754_logl): Likewise. --- ChangeLog | 8 ++++++++ NEWS | 4 ++-- sysdeps/i386/fpu/e_logl.S | 5 ++++- sysdeps/i386/i686/fpu/e_logl.S | 5 ++++- sysdeps/x86_64/fpu/e_logl.S | 5 ++++- 5 files changed, 22 insertions(+), 5 deletions(-) diff --git a/ChangeLog b/ChangeLog index 997cec6..3204c4e 100644 --- a/ChangeLog +++ b/ChangeLog @@ -1,3 +1,11 @@ +2014-06-18 Joseph Myers + + [BZ #17022] + * sysdeps/i386/fpu/e_logl.S (__ieee754_logl): Do not subtract 1 + from arguments -2 or below. + * sysdeps/i386/i686/fpu/e_logl.S (__ieee754_logl): Likewise. + * sysdeps/x86_64/fpu/e_logl.S (__ieee754_logl): Likewise. + 2014-06-18 Andreas Schwab [BZ #17062] diff --git a/NEWS b/NEWS index 429dba5..0c4d8bb 100644 --- a/NEWS +++ b/NEWS @@ -19,8 +19,8 @@ Version 2.20 16791, 16796, 16799, 16800, 16815, 16823, 16824, 16831, 16838, 16849, 16854, 16876, 16877, 16878, 16882, 16885, 16888, 16890, 16912, 16915, 16916, 16917, 16922, 16927, 16928, 16932, 16943, 16958, 16965, 16966, - 16967, 16977, 16978, 16984, 16990, 16996, 17009, 17031, 17042, 17048, - 17058, 17062. + 16967, 16977, 16978, 16984, 16990, 16996, 17009, 17022, 17031, 17042, + 17048, 17058, 17062. * The minimum Linux kernel version that this version of the GNU C Library can be used with is 2.6.32. diff --git a/sysdeps/i386/fpu/e_logl.S b/sysdeps/i386/fpu/e_logl.S index edae1d7..828e98a 100644 --- a/sysdeps/i386/fpu/e_logl.S +++ b/sysdeps/i386/fpu/e_logl.S @@ -40,8 +40,11 @@ ENTRY(__ieee754_logl) fld %st // x : x : log(2) sahf jc 3f // in case x is NaN or +-Inf + movzwl 4+8(%esp), %eax + cmpl $0xc000, %eax + jae 6f // x <= -2, avoid overflow from -LDBL_MAX - 1. 4: fsubl MO(one) // x-1 : x : log(2) - fld %st // x-1 : x-1 : x : log(2) +6: fld %st // x-1 : x-1 : x : log(2) fabs // |x-1| : x-1 : x : log(2) fcompl MO(limit) // x-1 : x : log(2) fnstsw // x-1 : x : log(2) diff --git a/sysdeps/i386/i686/fpu/e_logl.S b/sysdeps/i386/i686/fpu/e_logl.S index a0d1107..0ccc8fc 100644 --- a/sysdeps/i386/i686/fpu/e_logl.S +++ b/sysdeps/i386/i686/fpu/e_logl.S @@ -39,8 +39,11 @@ ENTRY(__ieee754_logl) LOAD_PIC_REG (dx) #endif fld %st // x : x : log(2) + movzwl 4+8(%esp), %eax + cmpl $0xc000, %eax + jae 5f // x <= -2, avoid overflow from -LDBL_MAX - 1. fsubl MO(one) // x-1 : x : log(2) - fld %st // x-1 : x-1 : x : log(2) +5: fld %st // x-1 : x-1 : x : log(2) fabs // |x-1| : x-1 : x : log(2) fld MO(limit) // 0.29 : |x-1| : x-1 : x : log(2) fcomip %st(1) // |x-1| : x-1 : x : log(2) diff --git a/sysdeps/x86_64/fpu/e_logl.S b/sysdeps/x86_64/fpu/e_logl.S index 315afc0..047b8db 100644 --- a/sysdeps/x86_64/fpu/e_logl.S +++ b/sysdeps/x86_64/fpu/e_logl.S @@ -38,8 +38,11 @@ ENTRY(__ieee754_logl) fld %st // x : x : log(2) testb $1, %ah jnz 3f // in case x is NaN or +-Inf + movzwl 8+8(%rsp), %eax + cmpl $0xc000, %eax + jae 6f // x <= -2, avoid overflow from -LDBL_MAX - 1. 4: fsubl MO(one) // x-1 : x : log(2) - fld %st // x-1 : x-1 : x : log(2) +6: fld %st // x-1 : x-1 : x : log(2) fabs // |x-1| : x-1 : x : log(2) fcompl MO(limit) // x-1 : x : log(2) fnstsw // x-1 : x : log(2) -- 2.7.4