From: Joseph Myers Date: Fri, 18 Sep 2015 20:34:59 +0000 (+0000) Subject: Avoid excess range in results from i386 scalb functions (bug 18981). X-Git-Tag: glibc-2.23~453 X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=94ced920a951bcab51f2ef955ccd2cc51668e6f3;p=thirdparty%2Fglibc.git Avoid excess range in results from i386 scalb functions (bug 18981). i386 scalb / scalbn / scalbln (and thus ldexp) functions for float and double can return results with excess range (and consequently excess precision for subnormal results). As the results of these functions are fully determined by reference to IEEE 754 operations, this is unambiguously a bug, apart from the testsuite failures it causes. This patch makes those functions store their results on the stack and load them back to eliminate the excess range. Double rounding is not a problem, as the only cases where it could occur are when the result overflows or underflows for extended precision, and then the double-rounded results are the same as the single-rounded results. The new macros will be used for more functions, more such macros added, and existing code refactored to use such macros, in subsequent patches. Tested for x86. Committed. [BZ #18981] * sysdeps/i386/fpu/i386-math-asm.h: New file. * sysdeps/i386/fpu/e_scalb.S: Include . (__ieee754_scalb): Use DBL_NARROW_EVAL. * sysdeps/i386/fpu/e_scalbf.S: Include . (__ieee754_scalbf): Use FLT_NARROW_EVAL. * sysdeps/i386/fpu/s_scalbn.S: Include . (__scalbn): Use DBL_NARROW_EVAL. * sysdeps/i386/fpu/s_scalbnf.S: Include . (__scalbnf): Use FLT_NARROW_EVAL. --- diff --git a/ChangeLog b/ChangeLog index 67c837da5ab..cafe59e3fb5 100644 --- a/ChangeLog +++ b/ChangeLog @@ -1,3 +1,16 @@ +2015-09-18 Joseph Myers + + [BZ #18981] + * sysdeps/i386/fpu/i386-math-asm.h: New file. + * sysdeps/i386/fpu/e_scalb.S: Include . + (__ieee754_scalb): Use DBL_NARROW_EVAL. + * sysdeps/i386/fpu/e_scalbf.S: Include . + (__ieee754_scalbf): Use FLT_NARROW_EVAL. + * sysdeps/i386/fpu/s_scalbn.S: Include . + (__scalbn): Use DBL_NARROW_EVAL. + * sysdeps/i386/fpu/s_scalbnf.S: Include . + (__scalbnf): Use FLT_NARROW_EVAL. + 2015-09-18 Wilco Dijkstra * math/w_tgamma.c (__ieee754_gamma_r): Use explicit sign check. diff --git a/NEWS b/NEWS index 8f487fac8d6..4d65df21b81 100644 --- a/NEWS +++ b/NEWS @@ -16,7 +16,7 @@ Version 2.23 18647, 18661, 18674, 18675, 18681, 18757, 18778, 18781, 18787, 18789, 18790, 18795, 18796, 18820, 18823, 18824, 18857, 18863, 18870, 18872, 18873, 18875, 18887, 18921, 18951, 18952, 18961, 18966, 18967, 18970, - 18977. + 18977, 18981. * The obsolete header has been removed. Programs that require this header must be updated to use instead. diff --git a/sysdeps/i386/fpu/e_scalb.S b/sysdeps/i386/fpu/e_scalb.S index 6a01aa64d69..370924c29fb 100644 --- a/sysdeps/i386/fpu/e_scalb.S +++ b/sysdeps/i386/fpu/e_scalb.S @@ -6,6 +6,7 @@ */ #include +#include .section .rodata @@ -52,6 +53,7 @@ ENTRY(__ieee754_scalb) jne 4f fscale fstp %st(1) + DBL_NARROW_EVAL ret /* y is -inf */ diff --git a/sysdeps/i386/fpu/e_scalbf.S b/sysdeps/i386/fpu/e_scalbf.S index 12b25159ace..4f2dfa3acf7 100644 --- a/sysdeps/i386/fpu/e_scalbf.S +++ b/sysdeps/i386/fpu/e_scalbf.S @@ -7,6 +7,7 @@ */ #include +#include .section .rodata @@ -54,6 +55,7 @@ ENTRY(__ieee754_scalbf) jne 4f fscale fstp %st(1) + FLT_NARROW_EVAL ret /* y is -inf */ diff --git a/sysdeps/i386/fpu/i386-math-asm.h b/sysdeps/i386/fpu/i386-math-asm.h new file mode 100644 index 00000000000..fd4313016cd --- /dev/null +++ b/sysdeps/i386/fpu/i386-math-asm.h @@ -0,0 +1,39 @@ +/* Helper macros for x86 libm functions. + Copyright (C) 2015 Free Software Foundation, Inc. + This file is part of the GNU C Library. + + The GNU C Library is free software; you can redistribute it and/or + modify it under the terms of the GNU Lesser General Public + License as published by the Free Software Foundation; either + version 2.1 of the License, or (at your option) any later version. + + The GNU C Library is distributed in the hope that it will be useful, + but WITHOUT ANY WARRANTY; without even the implied warranty of + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU + Lesser General Public License for more details. + + You should have received a copy of the GNU Lesser General Public + License along with the GNU C Library; if not, see + . */ + +#ifndef _I386_MATH_ASM_H +#define _I386_MATH_ASM_H 1 + +/* Remove excess range and precision by storing a value on the stack + and loading it back. */ +#define FLT_NARROW_EVAL \ + subl $4, %esp; \ + cfi_adjust_cfa_offset (4); \ + fstps (%esp); \ + flds (%esp); \ + addl $4, %esp; \ + cfi_adjust_cfa_offset (-4); +#define DBL_NARROW_EVAL \ + subl $8, %esp; \ + cfi_adjust_cfa_offset (8); \ + fstpl (%esp); \ + fldl (%esp); \ + addl $8, %esp; \ + cfi_adjust_cfa_offset (-8); + +#endif /* i386-math-asm.h. */ diff --git a/sysdeps/i386/fpu/s_scalbn.S b/sysdeps/i386/fpu/s_scalbn.S index dab75801c52..4e909031153 100644 --- a/sysdeps/i386/fpu/s_scalbn.S +++ b/sysdeps/i386/fpu/s_scalbn.S @@ -4,6 +4,7 @@ */ #include +#include RCSID("$NetBSD: s_scalbn.S,v 1.4 1995/05/09 00:19:06 jtc Exp $") @@ -12,6 +13,7 @@ ENTRY(__scalbn) fldl 4(%esp) fscale fstp %st(1) + DBL_NARROW_EVAL ret END (__scalbn) strong_alias (__scalbn, __scalbln) diff --git a/sysdeps/i386/fpu/s_scalbnf.S b/sysdeps/i386/fpu/s_scalbnf.S index ad97be86f40..f8353c4c75b 100644 --- a/sysdeps/i386/fpu/s_scalbnf.S +++ b/sysdeps/i386/fpu/s_scalbnf.S @@ -4,6 +4,7 @@ */ #include +#include RCSID("$NetBSD: s_scalbnf.S,v 1.3 1995/05/09 00:19:59 jtc Exp $") @@ -12,6 +13,7 @@ ENTRY(__scalbnf) flds 4(%esp) fscale fstp %st(1) + FLT_NARROW_EVAL ret END (__scalbnf) strong_alias (__scalbnf, __scalblnf)