string/FreeBSD/ffs.3

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  30 .\"     @(#)ffs.3       8.2 (Berkeley) 4/19/94
  31 .\" $FreeBSD: src/lib/libc/string/ffs.3,v 1.13 2009/01/13 13:19:42 kib Exp $
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  33 .Dd October 26, 2008
  34 .Dt FFS 3
  35 .Os
  36 .Sh NAME
  37 .Nm ffs ,
  38 .Nm ffsl ,
  39 .Nm fls ,
  40 .Nm flsl
  41 .Nd find first or last bit set in a bit string
  42 .Sh LIBRARY
  43 .Lb libc
  44 .Sh SYNOPSIS
  45 .In strings.h
  46 .Ft int
  47 .Fn ffs "int i"
  48 .Ft int
  49 .Fn ffsl "long i"
  50 .Ft int
  51 .Fn fls "int i"
  52 .Ft int
  53 .Fn flsl "long i"
  54 .Sh DESCRIPTION
  55 The
  56 .Fn ffs
  57 and
  58 .Fn ffsl
  59 functions find the first bit set
  60 (beginning with the least significant bit)
  61 in
  62 .Fa i
  63 and return the index of that bit.
  64 .Pp
  65 The
  66 .Fn fls
  67 and
  68 .Fn flsl
  69 functions find the last bit set in
  70 .Fa i
  71 and return the index of that bit.
  72 .Pp
  73 Bits are numbered starting at 1 (the least significant bit).
  74 A return value of zero from any of these functions means that the
  75 argument was zero.
  76 .Sh SEE ALSO
  77 .Xr bitstring 3
  78 .Sh HISTORY
  79 The
  80 .Fn ffs
  81 function appeared in
  82 .Bx 4.3 .
  83 Its prototype existed previously in
  84 .In string.h
  85 before it was moved to
  86 .In strings.h
  87 for
  88 .St -p1003.1-2001
  89 compliance.
  90 .Pp
  91 The
  92 .Fn ffsl ,
  93 .Fn fls ,
  94 and
  95 .Fn flsl
  96 functions appeared in
  97 .Fx 5.3 .