Mercurial > gnulib
view lib/log2f.c @ 37246:5cfb3a67238d
regex: avoid glibc deadlock during configure
glibc has a known bug where certain corruptions of the heap can
cause malloc to default to printing a debug message that includes
a backtrace, but the act of getting the backtrace uses dlopen
which in turn calls into malloc, causing a recursive lock ending
in deadlock. Thus, when configure is probing for a known glibc
heap corruption bug, the overall configure would hang.
The solution suggested by glibc developers is to force malloc
to quit printing debug messages, which avoids recursive malloc.
* m4/regex.m4 (gl_REGEX): Avoid recursive malloc deadlock when
glibc bug 15078 in turn triggers bug 16159.
Reported by Michal Privoznik.
Signed-off-by: Eric Blake <eblake@redhat.com>
author | Eric Blake <eblake@redhat.com> |
---|---|
date | Tue, 03 Dec 2013 10:34:13 -0700 |
parents | c741bc27922a |
children | 344018b6e5d7 |
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/* Base 2 logarithm. Copyright (C) 2012-2013 Free Software Foundation, Inc. This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 3 of the License, or (at your option) any later version. This program 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 General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <http://www.gnu.org/licenses/>. */ #include <config.h> /* Specification. */ #include <math.h> #if HAVE_LOG2 float log2f (float x) { return (float) log2 ((double) x); } #else /* Best possible approximation of log(2) as a 'float'. */ #define LOG2 0.693147180559945309417232121458176568075f /* Best possible approximation of 1/log(2) as a 'float'. */ #define LOG2_INVERSE 1.44269504088896340735992468100189213743f /* sqrt(0.5). */ #define SQRT_HALF 0.707106781186547524400844362104849039284f float log2f (float x) { if (isnanf (x)) return x; if (x <= 0.0f) { if (x == 0.0f) /* Return -Infinity. */ return - HUGE_VALF; else { /* Return NaN. */ #if defined _MSC_VER static float zero; return zero / zero; #else return 0.0f / 0.0f; #endif } } /* Decompose x into x = 2^e * y where e is an integer, 1/2 < y < 2. Then log2(x) = e + log2(y) = e + log(y)/log(2). */ { int e; float y; y = frexpf (x, &e); if (y < SQRT_HALF) { y = 2.0f * y; e = e - 1; } return (float) e + logf (y) * LOG2_INVERSE; } } #endif