@node rand48, random number
@subheading Syntax

@example
#include <stdlib.h>

double drand48(void);
double erand48(unsigned short state[3]);
unsigned long lrand48(void);
unsigned long nrand48(unsigned short state[3]);
long mrand48(void);
long jrand48(unsigned short state[3]);
void srand48(long seed);
unsigned short *seed48(unsigned short state_seed[3]);
void lcong48(unsigned short param[7]);
@end example

@subheading Description

This is the family of @code{*rand48} functions.  The basis for these functions
is the linear congruential formula @math{X[n+1] = (a*X[n] + c) mod 2^48,
n >= 0}.  a = 0x5deece66d and c = 0xb at start and after a call to either
@code{srand48} or @code{seed48}.  A call to @code{lcong48}
changes a and c (and the internal state). 

@code{drand48} and @code{erand48} return @code{double}s uniformly
distributed in the interval [0.0, 1.0). 

@code{lrand48} and @code{nrand48} return @code{unsigned long}s
uniformly distributed in the interval [0, 2^31).

@code{mrand48} and @code{jrand48} return @code{long}s uniformly
distributed in the interval [-2^31, 2^31). 

@code{erand48}, @code{jrand48} and @code{nrand48} requires the
state of the random generator to be passed.  

@code{drand48}, @code{lrand48} and @code{mrand48} uses an
internal state (common with all three functions) which should be
initialized with a call to one of the functions @code{srand48},
@code{seed48} or @code{lcong48}. 

@code{srand48} sets the high order 32 bits to the argument
@var{seed}.  The low order 16 bits are set to the arbitrary value
0x330e. 

@code{seed48} sets the internal state according to the argument
@var{state_seed} (@code{@var{state_seed}[0]} is least significant).
The previous state of the random generator is saved in an internal
(static) buffer, to which a pointer is returned. 

@code{lcong48} sets the internal state to @code{@var{param}[0-2]}, a to 
@code{@var{param}[3-5]} (@code{@var{param}[0]} and @code{@var{param}[3]}
are least significant) and c to @code{@var{param}[6]}. 

@subheading Return Value

A random number.

@subheading Portability

@portability !ansi, !posix

@subheading Example

@example
#include <stdio.h>
#include <stdlib.h>
#include <time.h>

int main(void)
@{

  srand48(time(NULL));
  printf("%.12f is a random number in [0.0, 1.0).\n", drand48());

  exit(0);
@}

@end example