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fls.c
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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 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 }
Datum bit(PG_FUNCTION_ARGS)
Definition: varbit.c:361
int fls(int mask)
Definition: fls.c:55