Updated: 1993-07-02

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#include <stdlib.h>double drand48(void);double erand48(unsigned shortxsubi[3]);long int lrand48(void);long int nrand48(unsigned shortxsubi[3]);long int mrand48(void);long int jrand48(unsigned shortxsubi[3]);void srand48(long intseedval);unsigned short *seed48(unsigned shortseed16v[3]);void lcong48(unsigned shortparam[7]);

The **drand48**() and **erand48**() functions return non-negative
double-precision floating-point values uniformly distributed between
[0.0, 1.0).

The **lrand48**() and **nrand48**() functions return non-negative
long integers uniformly distributed between 0 and 2^31.

The **mrand48**() and **jrand48**() functions return signed long
integers uniformly distributed between -2^31 and 2^31.

The **srand48**(), **seed48**() and **lcong48**() functions are
initialization functions, one of which should be called before using
**drand48**(), **lrand48**() or **mrand48**(). The functions
**erand48**(), **nrand48**() and **jrand48**() do not require
an initialization function to be called first.

All the functions work by generating a sequence of 48-bit integers,
*Xi*, according to the linear congruential formula:

**Xn+1 = (aXn + c) mod m, where n >= 0**

The parameter *m* = 2^48, hence 48-bit integer arithmetic is performed.
Unless **lcong48**() is called, *a* and *c* are given by:

**a = 0x5DEECE66D****c = 0xB**

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

The functions **drand48**(), **lrand48**() and **mrand48**() store
the last 48-bit *Xi* generated in an internal buffer. The functions
**erand48**(), **nrand48**() and **jrand48**() require the calling
program to provide storage for the successive *Xi* values in the array
argument *xsubi*. The functions are initialized by placing the initial
value of *Xi* into the array before calling the function for the first
time.

The initializer function **srand48**() sets the high order 32-bits of
*Xi* to the argument *seedval*. The low order 16-bits are set
to the arbitrary value 0x330E.

The initializer function **seed48**() sets the value of *Xi* to
the 48-bit value specified in the array argument *seed16v*. The
previous value of *Xi* is copied into an internal buffer and a
pointer to this buffer is returned by **seed48**().

The initialization function **lcong48**() allows the user to specify
initial values for *Xi*, *a* and *c*. Array argument
elements *param[0-2]* specify *Xi*, *param[3-5]* specify
*a*, and *param[6]* specifies *c*. After **lcong48**()
has been called, a subsequent call to either **srand48**() or
**seed48**() will restore the standard values of *a* and *c*.

- NAME
- SYNOPSIS
- DESCRIPTION
- CONFORMING TO
- NOTES
- SEE ALSO