Line data    Source code

       1             : /*-------------------------------------------------------------------------
       2             :  *
       3             :  * fls.c
       4             :  *    finds the last (most significant) bit that is set
       5             :  *
       6             :  * Portions Copyright (c) 1996-2017, 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         134 : fls(int mask)
      56             : {
      57             :     int         bit;
      58             : 
      59         134 :     if (mask == 0)
      60          68 :         return (0);
      61         236 :     for (bit = 1; mask != 1; bit++)
      62         170 :         mask = (unsigned int) mask >> 1;
      63          66 :     return (bit);
      64             : }