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

#include<stdlib.h>doubledrand48(void);doubleerand48(unsignedshortintxsubi[3]);longintlrand48(void);longintnrand48(unsignedshortintxsubi[3]);longintmrand48(void);longintjrand48(unsignedshortintxsubi[3]);voidsrand48(longintseedval);unsignedshortint*seed48(unsignedshortintseed16v[3]);voidlcong48(unsignedshortintparam[7]);

These functions generate pseudo-random numbers using the linear congruential algorithm and 48-bit integer arith metic. Thedrand48()anderand48()functions return non-negative double-precision floating-point values uniformly dis tributed between [0.0, 1.0). Thelrand48()andnrand48()functions return non-negative long integers uniformly distributed between 0 and 2^31. Themrand48()andjrand48()functions return signed long integers uniformly distributed between -2^31 and 2^31. Thesrand48(),seed48()andlcong48()functions are ini tialization functions, one of which should be called before usingdrand48(),lrand48()ormrand49(). The func tionserand48(),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 for mula:Xn+1=(aXn+c)modm,wheren>=0by:a=0x5DEECE66Dc=0xBThe value returned by any of the functionsdrand48(),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 functionsdrand48(),lrand48()andmrand48()store the last 48-bitXigenerated in an internal buffer. The func tionserand48(),nrand48()andjrand48()require the call ing program to provide storage for the successiveXival ues in the array argumentxsubi. The functions are ini tialized by placing the initial value ofXiinto the array before calling the function for the first time. The initializer functionsrand48()sets the high order 32-bits ofXito the argumentseedval. The low order 16-bits are set to the arbitrary value 0x330E. The initializer functionseed48()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 functionlcong48()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.

SVID 3

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

rand(3),random(3)