# jrand48(3c) [opensolaris man page]

```drand48(3C)						   Standard C Library Functions 					       drand48(3C)

NAME
drand48, erand48, lrand48, nrand48, mrand48, jrand48, srand48, seed48, lcong48 - generate uniformly distributed pseudo-random numbers

SYNOPSIS
#include <stdlib.h>

double drand48(void)

double erand48(unsigned short x(i)[3]);

long lrand48(void)

long nrand48(unsigned short x(i)[3]);

long mrand48(void)

long jrand48(unsigned short x(i)[3]);

void srand48(long seedval);

unsigned short *seed48(unsigned short seed16v[3]);

void lcong48(unsigned short param[7]);

DESCRIPTION
This family of functions generates pseudo-random numbers using the well-known linear congruential algorithm and 48-bit integer arithmetic.

Functions  drand48() and erand48() return non-negative double-precision floating-point values uniformly distributed over the interval [0.0,
1.0).

Functions lrand48() and nrand48() return non-negative long integers uniformly distributed over the interval [0, 2  ^31 ].

Functions mrand48() and jrand48() return signed long integers uniformly distributed over the interval [-2 ^31  , 2 ^31  ].

Functions srand48(), seed48(), and lcong48() are initialization entry points, one of which  should  be  invoked	before	either	drand48(),
lrand48(), or mrand48() is called. (Although it is not recommended practice, constant default initializer values will be supplied automati-
cally if drand48(), lrand48(), or mrand48() is called without a	prior  call  to  an  initialization  entry  point.)  Functions	erand48(),
nrand48(), and jrand48() do not require an initialization entry point to be called first.

All the routines work by generating a sequence of 48-bit integer values, X(i ), according to the linear congruential formula

X(n+1)= (aX (n)+c)(mod m) n>=0.

The  parameter  m  =  2^48;  hence 48-bit integer arithmetic is performed. Unless lcong48() has been invoked, the multiplier value aand the
addend value care given by
a = 5DEECE66D(16) = 273673163155(8)
c = B(16) = 13(8)

The value returned by any of the functions drand48(), erand48(), lrand48(), nrand48(), mrand48(), or jrand48() is computed by first  gener-
ating  the  next  48-bit  X(i) in the sequence. Then the appropriate number of bits, according to the type of data item to be returned, are
copied from the high-order (leftmost) bits of X(i) and transformed into the returned value.

The functions drand48(), lrand48(), and mrand48() store the last 48-bit X(i) generated in an internal  buffer.  X(i)  must  be  initialized
prior to being invoked. The functions erand48(), nrand48(), and jrand48() require the calling program to provide storage for the successive
X(i) values in the array specified as an argument when the functions are invoked. These routines do not have to be initialized; the calling
program	must  place  the  desired initial value of X(i) into the array and pass it as an argument. By using different arguments, functions
erand48(), nrand48(), and jrand48() allow separate modules of a large program to generate several independent streams of pseudo-random num-
bers, that is, the sequence of numbers in each stream will not depend upon how many times the routines have been called to generate numbers
for the other streams.

The initializer function srand48() sets the high-order 32 bits of X(i) to the 32 bits contained in its argument. The low-order 16  bits	of
X(i) are set to the arbitrary value 330E(16) .

The  initializer  function  seed48()  sets the value of X(i) to the 48-bit value specified in the argument array. In addition, the previous
value of X(i) is copied into a 48-bit internal buffer, used only by seed48(), and a pointer  to	this  buffer  is  the  value  returned	by
seed48().  This	returned pointer, which can just be ignored if not needed, is useful if a program is to be restarted from a given point at
some future time -- use the pointer to get at and store the last X(i) value, and then use this value to reinitialize  using  seed48()  when
the program is restarted.

The  initialization function lcong48() allows the user to specify the initial X(i) the multiplier value a, and the addend value c. Argument
array elements param[0-2] specify X(i), param[3-5] specify the multiplier a, and param[6] specifies the 16-bit addend  c.  After  lcong48()
has  been  called,  a  subsequent call to either srand48() or seed48() will restore the ``standard'' multiplier and addend values, a and c,
specified above.

ATTRIBUTES
See attributes(5) for descriptions of the following attributes:

+-----------------------------+-----------------------------+
|      ATTRIBUTE TYPE	     |	    ATTRIBUTE VALUE	   |
+-----------------------------+-----------------------------+
|Interface Stability	     |Standard			   |
+-----------------------------+-----------------------------+
|MT-Level		     |Safe			   |
+-----------------------------+-----------------------------+