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'\" te .\" Portions Copyright (c) 2002, 2022, Oracle and/or its affiliates. .\" Copyright (c) 1989, AT&T. All rights reserved. .TH drand48 3C "10 Mar 2022" "Oracle Solaris 11.4" "Standard C Library Functions" .SH NAME drand48, erand48, lrand48, nrand48, mrand48, jrand48, srand48, seed48, lcong48 \- generate uniformly distributed pseudo-random numbers .SH SYNOPSIS .LP .nf #include <stdlib.h> \fBdouble\fR \fBdrand48\fR(void) .fi .LP .nf \fBdouble\fR \fBerand48\fR(\fBunsigned short\fR \fIxsubi\fR[3]); .fi .LP .nf \fBlong\fR \fBlrand48\fR(void) .fi .LP .nf \fBlong\fR \fBnrand48\fR(\fBunsigned short\fR \fIxsubi\fR[3]); .fi .LP .nf \fBlong\fR \fBmrand48\fR(void) .fi .LP .nf \fBlong\fR \fBjrand48\fR(\fBunsigned short\fR \fIxsubi\fR[3]); .fi .LP .nf \fBvoid\fR \fBsrand48\fR(\fBlong\fR \fIseedval\fR); .fi .LP .nf \fBunsigned short *\fR\fBseed48\fR(\fBunsigned short\fR \fIseed16v\fR[3]); .fi .LP .nf \fBvoid\fR \fBlcong48\fR(\fBunsigned short\fR \fIparam\fR[7]); .fi .LP .nf \fBint\fR \fBdrand48_r\fR(\fBstruct drand48_data *\fR\fIbuffer\fR, \fBdouble *\fR\fIresult\fR); .fi .LP .nf \fBint\fR \fBerand48_r\fR(\fBunsigned short\fR \fIxsubi\fR[3], \fBstruct drand48_data *\fR\fIbuf\fR, \fBdouble *\fR\fIresult\fR); .fi .LP .nf \fBint\fR \fBlrand48_r\fR(\fBstruct drand48_data *\fR\fIbuf\fR, \fBlong int *\fR\fIresult\fR); .fi .LP .nf \fBint\fR \fBnrand48_r\fR(\fBunsigned short int\fR \fIxsubi\fR[3], \fBstruct drand48_data *\fR\fIbuf\fR, \fBlong int *\fR\fIresult\fR); .fi .LP .nf \fBint\fR \fBmrand48_r\fR(\fBstruct drand48_data *\fR\fIbuf\fR, \fBlong int *\fR\fIresult\fR); .fi .LP .nf \fBint\fR \fBjrand48_r\fR(\fBunsigned short int\fR \fIxsubi\fR[3], \fBstruct drand48_data *\fR\fIbuf\fR, \fBlong int *\fR\fIresult\fR); .fi .LP .nf \fBint\fR \fBsrand48_r\fR(\fBlong int\fR \fIseedval\fR, \fBstruct drand48_data *\fR\fIbuf\fR); .fi .LP .nf \fBint\fR \fBseed48_r\fR(\fBunsigned short int\fR \fIseed16v\fR[3], \fBstruct drand48_data *\fR\fIbuf\fR); .fi .LP .nf \fBint\fR \fBlcong48_r\fR(\fBunsigned short int\fR \fIparam\fR[7], \fBstruct drand48_data *\fR\fIbuf\fR); .fi .SH DESCRIPTION .sp .LP This family of functions generates pseudo-random numbers using the well-known linear congruential algorithm and 48-bit integer arithmetic. .sp .LP Functions \fBdrand48()\fR and \fBerand48()\fR return non-negative double-precision floating-point values uniformly distributed over the interval [0.0, 1.0). .sp .LP Functions \fBlrand48()\fR and \fBnrand48()\fR return non-negative long integers uniformly distributed over the interval [0, 2 ^31 ]. .sp .LP Functions \fBmrand48()\fR and \fBjrand48()\fR return signed long integers uniformly distributed over the interval [-2 ^31 , 2 ^31 ]. .sp .LP Functions \fBsrand48()\fR, \fBseed48()\fR, and \fBlcong48()\fR are initialization entry points, one of which should be invoked before either \fBdrand48()\fR, \fBlrand48()\fR, or \fBmrand48()\fR is called. (Although it is not recommended practice, constant default initializer values will be supplied automatically if \fBdrand48()\fR, \fBlrand48()\fR, or \fBmrand48()\fR is called without a prior call to an initialization entry point.) Functions \fBerand48()\fR, \fBnrand48()\fR, and \fBjrand48()\fR do not require an initialization entry point to be called first. .sp .LP All the routines work by generating a sequence of 48-bit integer values, X(i), according to the linear congruential formula .sp .LP X(n+1)= (aX (n)+c)(mod m) n>=0. .sp .LP The parameter \fIm\fR = 2^48; hence 48-bit integer arithmetic is performed. Unless \fBlcong48()\fR has been invoked, the multiplier value \fIa\fR and the addend value \fIc\fR are given by .br .in +2 \fIa\fR = 5DEECE66D(16) = 273673163155(8) .in -2 .br .in +2 \fIc\fR = B(16) = 13(8) .in -2 .sp .LP The value returned by any of the functions \fBdrand48()\fR, \fBerand48()\fR, \fBlrand48()\fR, \fBnrand48()\fR, \fBmrand48()\fR, or \fBjrand48()\fR is computed by first generating 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. .sp .LP The functions \fBdrand48()\fR, \fBlrand48()\fR, and \fBmrand48()\fR store the last 48-bit X(i) generated in an internal buffer. X(i) must be initialized prior to being invoked. The functions \fBerand48()\fR, \fBnrand48()\fR, and \fBjrand48()\fR 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 \fBerand48()\fR, \fBnrand48()\fR, and \fBjrand48()\fR allow separate modules of a large program to generate several \fIindependent\fR streams of pseudo-random numbers, that is, the sequence of numbers in each stream will \fInot\fR depend upon how many times the routines have been called to generate numbers for the other streams. .sp .LP The initializer function \fBsrand48()\fR 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) . .sp .LP The initializer function \fBseed48()\fR 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 \fBseed48()\fR, and a pointer to this buffer is the value returned by \fBseed48()\fR. 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 \(em use the pointer to get at and store the last X(i) value, and then use this value to reinitialize using \fBseed48()\fR when the program is restarted. .sp .LP The initialization function \fBlcong48()\fR allows the user to specify the initial X(i) the multiplier value \fIa\fR, and the addend value \fIc\fR. Argument array elements \fIparam[0-2]\fR specify X(i), \fIparam[3-5]\fR specify the multiplier \fIa\fR, and \fIparam\fR[6] specifies the 16-bit addend \fIc\fR. After \fBlcong48()\fR has been called, a subsequent call to either \fBsrand48()\fR or \fBseed48()\fR will restore the "standard" multiplier and addend values, \fIa\fR and \fIc\fR, specified above. .sp .LP Functions \fBdrand48_r()\fR, \fBerand48_r()\fR, \fBjrand48_r()\fR, \fBlrand48_r()\fR, \fBmrand_r()\fR, and \fBnrand_r()\fR are reentrant versions of \fBdrand48()\fR, \fBerand48()\fR, \fBjrand48()\fR, \fBlrand48()\fR, \fBmrand48()\fR, and \fBnrand48()\fR functions. They use the supplied buffer, \fIbuf\fR, to store the random number generator state, as opposed to the global buffers used by the non-reentrant functions. The buffer must be first allocated, and then initialized either by filling with zeroes, or by calling one of the \fBsrand48_r()\fR, \fBseed48_r()\fR, or \fBlcong48_r()\fR functions. .sp .LP Functions \fBsrand48_r()\fR, \fBseed48_r()\fR, and \fBlcong48_r()\fR are reentrant versions of the functions \fBsrand48()\fR, \fBseed48()\fR, and \fBlcong48()\fR. In addition, they can be used to initialize the supplied buffer, \fIbuf\fR. .SH USAGE .sp .LP Programmers should use \fB/dev/urandom\fR or \fB/dev/random\fR for most random-number generation, especially for cryptographic purposes. See \fBgetrandom\fR(2) and \fBrandom\fR(4D). .SH ATTRIBUTES .sp .LP See \fBattributes\fR(7) for descriptions of the following attributes: .sp .TS tab( ) box; cw(2.75i) |cw(2.75i) lw(2.75i) |lw(2.75i) . ATTRIBUTE TYPE ATTRIBUTE VALUE _ Interface Stability Committed _ MT-Level Safe _ Standard See \fBstandards\fR(7). .TE .sp .SH SEE ALSO .sp .LP \fBgetrandom\fR(2), \fBrand\fR(3C), \fBrandom\fR(4D), \fBattributes\fR(7), \fBstandards\fR(7)