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

Synopsis

Description

Notes

Colophon

#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]);Feature Test Macro Requirements for glibc (see

feature_test_macros(7)):All functions shown above: _SVID_SOURCE || _XOPEN_SOURCE

These functions generate pseudo-random numbers using the linear congruential algorithm and 48-bit integer arithmetic.The

drand48() anderand48() functions return nonnegative double-precision floating-point values uniformly distributed between [0.0, 1.0).The

lrand48() andnrand48() functions return nonnegative long integers uniformly distributed between 0 and 2^31.The

mrand48() andjrand48() functions return signed long integers uniformly distributed between -2^31 and 2^31.The

srand48(),seed48() andlcong48() functions are initialization functions, one of which should be called before usingdrand48(),lrand48() ormrand48(). The functionserand48(),nrand48() andjrand48() 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 >= 0The parameter

m= 2^48, hence 48-bit integer arithmetic is performed. Unlesslcong48() is called,aandcare given by:

a = 0x5DEECE66Dc = 0xBThe value returned by any of the functions

drand48(),erand48(),lrand48(),nrand48(),mrand48() orjrand48() is computed by first generating the next 48-bitXiin 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 ofXiand transformed into the returned value.The functions

drand48(),lrand48() andmrand48() store the last 48-bitXigenerated in an internal buffer. The functionserand48(),nrand48() andjrand48() require the calling program to provide storage for the successiveXivalues in the array argumentxsubi. The functions are initialized by placing the initial value ofXiinto the array before calling the function for the first time.The initializer function

srand48() sets the high order 32-bits ofXito the argumentseedval. The low order 16-bits are set to the arbitrary value 0x330E.The initializer function

seed48() sets the value ofXito the 48-bit value specified in the array argumentseed16v. The previous value ofXiis copied into an internal buffer and a pointer to this buffer is returned byseed48().The initialization function

lcong48() allows the user to specify initial values forXi,aandc. Array argument elementsparam[0-2]specifyXi,param[3-5]specifya, andparam[6]specifiesc. Afterlcong48() has been called, a subsequent call to eithersrand48() orseed48() will restore the standard values ofaandc.

SVr4, POSIX.1-2001.

These functions are declared obsolete by SVID 3, which states thatrand(3) should be used instead.

rand(3),random(3)

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DRAND48 (3) | 2007-07-26 |