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/* ffsl.h -- find the first set bit in a word.
Copyright (C) 2011-2013 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/>. */
/* Written by Eric Blake. */
/* This file is meant to be included by ffsl.c and ffsll.c, after
they have defined FUNC and TYPE. */
#include <config.h>
/* Specification. */
#include <string.h>
#include <limits.h>
#include <strings.h>
#if !defined FUNC || !defined TYPE
# error
#endif
int
FUNC (TYPE i)
{
#if (__GNUC__ > 3 || (__GNUC__ == 3 && __GNUC_MINOR__ >= 4)) && defined GCC_BUILTIN
return GCC_BUILTIN (i);
#else
unsigned TYPE j = i;
/* Split j into chunks, and look at one chunk after the other. */
enum { chunk_bits = CHAR_BIT * sizeof (unsigned int) };
/* The number of chunks is ceil (sizeof (TYPE) / sizeof (unsigned int))
= (sizeof (TYPE) - 1) / sizeof (unsigned int) + 1. */
enum { chunk_count = (sizeof (TYPE) - 1) / sizeof (unsigned int) + 1 };
if (chunk_count > 1)
{
size_t k;
/* It is tempting to write if (!j) here, but if we do this,
Solaris 10/x86 "cc -O" miscompiles the code. */
if (!i)
return 0;
/* Unroll the first loop round. k = 0. */
if ((unsigned int) j)
return ffs ((unsigned int) j);
/* Generic loop. */
for (k = 1; k < chunk_count - 1; k++)
if ((unsigned int) (j >> (k * chunk_bits)) != 0)
return k * chunk_bits + ffs ((unsigned int) (j >> (k * chunk_bits)));
}
/* Last loop round. k = chunk_count - 1. */
return (chunk_count - 1) * chunk_bits
+ ffs ((unsigned int) (j >> ((chunk_count - 1) * chunk_bits)));
#endif
}
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