src/port/fls.c

   1 /*-------------------------------------------------------------------------
   2  *
   3  * fls.c
   4  *        finds the last (most significant) bit that is set
   5  *
   6  * Portions Copyright (c) 1996-2020, PostgreSQL Global Development Group
   7  *
   8  *
   9  * IDENTIFICATION
  10  *        src/port/fls.c
  11  *
  12  * This file was taken from FreeBSD to provide an implementation of fls()
  13  * for platforms that lack it.  Note that the operating system's version may
  14  * be substantially more efficient than ours, since some platforms have an
  15  * assembly instruction that does exactly this.
  16  *
  17  * The FreeBSD copyright terms follow.
  18  */
  19
  20 /*-
  21  * Copyright (c) 1990, 1993
  22  *      The Regents of the University of California.  All rights reserved.
  23  *
  24  * Redistribution and use in source and binary forms, with or without
  25  * modification, are permitted provided that the following conditions
  26  * are met:
  27  * 1. Redistributions of source code must retain the above copyright
  28  *        notice, this list of conditions and the following disclaimer.
  29  * 2. Redistributions in binary form must reproduce the above copyright
  30  *        notice, this list of conditions and the following disclaimer in the
  31  *        documentation and/or other materials provided with the distribution.
  32  * 4. Neither the name of the University nor the names of its contributors
  33  *        may be used to endorse or promote products derived from this software
  34  *        without specific prior written permission.
  35  *
  36  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
  37  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  38  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  39  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
  40  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  41  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  42  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  43  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  44  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  45  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  46  * SUCH DAMAGE.
  47  */
  48
  49 #include "c.h"
  50
  51 /*
  52  * Find Last Set bit
  53  */
  54 int
  55 fls(int mask)
  56 {
  57         int                     bit;
  58
  59         if (mask == 0)
  60                 return (0);
  61         for (bit = 1; mask != 1; bit++)
  62                 mask = (unsigned int) mask >> 1;
  63         return (bit);
  64 }