myrand.c

[詳解]

/*++
/* NAME
/*  myrand 3
/* SUMMARY
/*  rand wrapper
/* SYNOPSIS
/*  #include <myrand.h>
/*
/*  void    mysrand(seed)
/*  int seed;
/*
/*  int myrand()
/* DESCRIPTION
/*  This module implements a wrapper for the portable, pseudo-random
/*  number generator. The wrapper adds automatic initialization.
/*
/*  mysrand() performs initialization. This call may be skipped.
/*
/*  myrand() returns a pseudo-random number in the range [0, RAND_MAX].
/*  If mysrand() was not called, it is invoked with the process ID
/*  ex-or-ed with the time of day in seconds.
/* LICENSE
/* .ad
/* .fi
/*  The Secure Mailer license must be distributed with this software.
/* WARNING
/*  Do not use this code for generating unpredictable numbers.
/* AUTHOR(S)
/*  Wietse Venema
/*  IBM T.J. Watson Research
/*  P.O. Box 704
/*  Yorktown Heights, NY 10598, USA
/*--*/

/* System library. */

#include <sys_defs.h>
#include <stdlib.h>
#include <unistd.h>
#include <time.h>

/* Utility library. */

#include <myrand.h>

static int myrand_initdone = 0;

/* mysrand - initialize */

void    mysrand(int seed)
{
    srand(seed);
    myrand_initdone = 1;
}

/* myrand - pseudo-random number */

int     myrand(void)
{
    if (myrand_initdone == 0)
    mysrand(getpid() ^ time((time_t *) 0));
    return (rand());
}