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diff --git a/man3/drand48.3 b/man3/drand48.3 new file mode 100644 index 0000000..b768d0d --- /dev/null +++ b/man3/drand48.3 @@ -0,0 +1,263 @@ +'\" t +.\" Copyright 1993 David Metcalfe (david@prism.demon.co.uk) +.\" +.\" SPDX-License-Identifier: Linux-man-pages-copyleft +.\" +.\" References consulted: +.\" Linux libc source code +.\" Lewine's _POSIX Programmer's Guide_ (O'Reilly & Associates, 1991) +.\" 386BSD man pages +.\" Modified Sat Jul 24 19:46:03 1993 by Rik Faith (faith@cs.unc.edu) +.TH drand48 3 2023-07-20 "Linux man-pages 6.05.01" +.SH NAME +drand48, erand48, lrand48, nrand48, mrand48, jrand48, srand48, seed48, +lcong48 \- generate uniformly distributed pseudo-random numbers +.SH LIBRARY +Standard C library +.RI ( libc ", " \-lc ) +.SH SYNOPSIS +.nf +.B #include <stdlib.h> +.PP +.B double drand48(void); +.BI "double erand48(unsigned short " xsubi [3]); +.PP +.B long lrand48(void); +.BI "long nrand48(unsigned short " xsubi [3]); +.PP +.B long mrand48(void); +.BI "long jrand48(unsigned short " xsubi [3]); +.PP +.BI "void srand48(long " seedval ); +.BI "unsigned short *seed48(unsigned short " seed16v [3]); +.BI "void lcong48(unsigned short " param [7]); +.fi +.PP +.RS -4 +Feature Test Macro Requirements for glibc (see +.BR feature_test_macros (7)): +.RE +.PP +All functions shown above: +.\" .BR drand48 (), +.\" .BR erand48 (), +.\" .BR lrand48 (), +.\" .BR nrand48 (), +.\" .BR mrand48 (), +.\" .BR jrand48 (), +.\" .BR srand48 (), +.\" .BR seed48 (), +.\" .BR lcong48 (): +.nf + _XOPEN_SOURCE + || /* glibc >= 2.19: */ _DEFAULT_SOURCE + || /* glibc <= 2.19: */ _SVID_SOURCE +.fi +.SH DESCRIPTION +These functions generate pseudo-random numbers using the linear congruential +algorithm and 48-bit integer arithmetic. +.PP +The +.BR drand48 () +and +.BR erand48 () +functions return nonnegative +double-precision floating-point values uniformly distributed over the interval +[0.0,\ 1.0). +.PP +The +.BR lrand48 () +and +.BR nrand48 () +functions return nonnegative +long integers uniformly distributed over the interval [0,\ 2\[ha]31). +.PP +The +.BR mrand48 () +and +.BR jrand48 () +functions return signed long +integers uniformly distributed over the interval [\-2\[ha]31,\ 2\[ha]31). +.PP +The +.BR srand48 (), +.BR seed48 (), +and +.BR lcong48 () +functions are +initialization functions, one of which should be called before using +.BR drand48 (), +.BR lrand48 (), +or +.BR mrand48 (). +The functions +.BR erand48 (), +.BR nrand48 (), +and +.BR jrand48 () +do not require +an initialization function to be called first. +.PP +All the functions work by generating a sequence of 48-bit integers, +.IR Xi , +according to the linear congruential formula: +.PP +.in +4n +.EX +.B Xn+1 = (aXn + c) mod m, where n >= 0 +.EE +.in +.PP +The parameter +.I m += 2\[ha]48, hence 48-bit integer arithmetic is performed. +Unless +.BR lcong48 () +is called, +.I a +and +.I c +are given by: +.PP +.in +4n +.EX +.B a = 0x5DEECE66D +.B c = 0xB +.EE +.in +.PP +The value returned by any of the functions +.BR drand48 (), +.BR erand48 (), +.BR lrand48 (), +.BR nrand48 (), +.BR mrand48 (), +or +.BR jrand48 () +is +computed by first generating the next 48-bit +.I 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 +.I Xi +and transformed +into the returned value. +.PP +The functions +.BR drand48 (), +.BR lrand48 (), +and +.BR mrand48 () +store +the last 48-bit +.I Xi +generated in an internal buffer. +The functions +.BR erand48 (), +.BR nrand48 (), +and +.BR jrand48 () +require the calling +program to provide storage for the successive +.I Xi +values in the array +argument +.IR xsubi . +The functions are initialized by placing the initial +value of +.I Xi +into the array before calling the function for the first +time. +.PP +The initializer function +.BR srand48 () +sets the high order 32-bits of +.I Xi +to the argument +.IR seedval . +The low order 16-bits are set +to the arbitrary value 0x330E. +.PP +The initializer function +.BR seed48 () +sets the value of +.I Xi +to +the 48-bit value specified in the array argument +.IR seed16v . +The +previous value of +.I Xi +is copied into an internal buffer and a +pointer to this buffer is returned by +.BR seed48 (). +.PP +The initialization function +.BR lcong48 () +allows the user to specify +initial values for +.IR Xi , +.IR a , +and +.IR c . +Array argument +elements +.I param[0\-2] +specify +.IR Xi , +.I param[3\-5] +specify +.IR a , +and +.I param[6] +specifies +.IR c . +After +.BR lcong48 () +has been called, a subsequent call to either +.BR srand48 () +or +.BR seed48 () +will restore the standard values of +.I a +and +.IR c . +.SH ATTRIBUTES +For an explanation of the terms used in this section, see +.BR attributes (7). +.TS +allbox; +lbx lb lb +l l l. +Interface Attribute Value +T{ +.na +.nh +.BR drand48 (), +.BR erand48 (), +.BR lrand48 (), +.BR nrand48 (), +.BR mrand48 (), +.BR jrand48 (), +.BR srand48 (), +.BR seed48 (), +.BR lcong48 () +T} Thread safety T{ +.na +.nh +MT-Unsafe race:drand48 +T} +.TE +.sp 1 +.PP +The above +functions record global state information for the random number generator, +so they are not thread-safe. +.SH STANDARDS +POSIX.1-2008. +.SH HISTORY +POSIX.1-2001, SVr4. +.SH SEE ALSO +.BR rand (3), +.BR random (3) |