stdlib/FreeBSD/rand.3

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  36 .\"     @(#)rand.3      8.1 (Berkeley) 6/4/93
  37 .\" $FreeBSD: src/lib/libc/stdlib/rand.3,v 1.13 2002/12/18 12:45:10 ru Exp $
  38 .\"
  39 .Dd May 25, 1999
  40 .Dt RAND 3
  41 .Os
  42 .Sh NAME
  43 .Nm rand ,
  44 .Nm srand ,
  45 .Nm sranddev ,
  46 .Nm rand_r
  47 .Nd bad random number generator
  48 .Sh LIBRARY
  49 .Lb libc
  50 .Sh SYNOPSIS
  51 .In stdlib.h
  52 .Ft void
  53 .Fn srand "unsigned seed"
  54 .Ft void
  55 .Fn sranddev void
  56 .Ft int
  57 .Fn rand void
  58 .Ft int
  59 .Fn rand_r "unsigned *ctx"
  60 .Sh DESCRIPTION
  61 .Bf -symbolic
  62 These interfaces are obsoleted by
  63 .Xr random 3 .
  64 .Ef
  65 .Pp
  66 The
  67 .Fn rand
  68 function computes a sequence of pseudo-random integers in the range
  69 of 0 to
  70 .Dv RAND_MAX
  71 (as defined by the header file
  72 .Aq Pa stdlib.h ) .
  73 .Pp
  74 The
  75 .Fn srand
  76 function sets its argument
  77 .Fa seed
  78 as the seed for a new sequence of
  79 pseudo-random numbers to be returned by
  80 .Fn rand .
  81 These sequences are repeatable by calling
  82 .Fn srand
  83 with the same seed value.
  84 .Pp
  85 If no
  86 .Fa seed
  87 value is provided, the functions are automatically
  88 seeded with a value of 1.
  89 .Pp
  90 The
  91 .Fn sranddev
  92 function initializes a seed using the
  93 .Xr random 4
  94 random number device which returns good random numbers,
  95 suitable for cryptographic use.
  96 .Pp
  97 The
  98 .Fn rand_r
  99 function
 100 provides the same functionality as
 101 .Fn rand .
 102 A pointer to the context value
 103 .Fa ctx
 104 must be supplied by the caller.
 105 .Sh SEE ALSO
 106 .Xr random 3 ,
 107 .Xr random 4
 108 .Sh STANDARDS
 109 The
 110 .Fn rand
 111 and
 112 .Fn srand
 113 functions
 114 conform to
 115 .St -isoC .
 116 .Pp
 117 The
 118 .Fn rand_r
 119 function is as proposed in the POSIX.4a Draft #6 document.