stdlib/rand.3

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  36 .\"     @(#)rand.3      8.1 (Berkeley) 6/4/93
  37 .\" $FreeBSD: src/lib/libc/stdlib/rand.3,v 1.14 2003/09/08 19:57:15 ru Exp $
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  39 .Dd May 25, 1999
  40 .Dt RAND 3
  41 .Os
  42 .Sh NAME
  43 .Nm rand ,
  44 .Nm rand_r ,
  45 .Nm srand ,
  46 .Nm sranddev
  47 .Nd bad random number generator
  48 .Sh LIBRARY
  49 .Lb libc
  50 .Sh SYNOPSIS
  51 .In stdlib.h
  52 .Ft int
  53 .Fo rand
  54 .Fa void
  55 .Fc
  56 .Ft int
  57 .Fo rand_r
  58 .Fa "unsigned *seed"
  59 .Fc
  60 .Ft void
  61 .Fo srand
  62 .Fa "unsigned seed"
  63 .Fc
  64 .Ft void
  65 .Fo sranddev
  66 .Fa void
  67 .Fc
  68 .Sh DESCRIPTION
  69 .Bf -symbolic
  70 These interfaces are obsoleted by
  71 .Xr random 3 .
  72 .Ef
  73 .Pp
  74 The
  75 .Fn rand
  76 function computes a sequence of pseudo-random integers in the range
  77 of 0 to
  78 .Dv RAND_MAX
  79 (as defined by the header file
  80 .In stdlib.h ) .
  81 .Pp
  82 The
  83 .Fn srand
  84 function sets its argument
  85 .Fa seed
  86 as the seed for a new sequence of
  87 pseudo-random numbers to be returned by
  88 .Fn rand .
  89 These sequences are repeatable by calling
  90 .Fn srand
  91 with the same seed value.
  92 .Pp
  93 If no
  94 .Fa seed
  95 value is provided, the functions are automatically
  96 seeded with a value of 1.
  97 .Pp
  98 The
  99 .Fn sranddev
 100 function initializes a seed, using the
 101 .Xr random 4
 102 random number device which returns good random numbers,
 103 suitable for cryptographic use.
 104 .Pp
 105 The
 106 .Fn rand_r
 107 function
 108 provides the same functionality as
 109 .Fn rand .
 110 A pointer to the context value
 111 .Fa seed
 112 must be supplied by the caller.
 113 .Sh SEE ALSO
 114 .Xr random 3 ,
 115 .Xr random 4
 116 .Sh STANDARDS
 117 The
 118 .Fn rand
 119 and
 120 .Fn srand
 121 functions
 122 conform to
 123 .St -isoC .
 124 .Pp
 125 The
 126 .Fn rand_r
 127 function is as proposed in the POSIX.4a Draft #6 document.