/* rng.c (pseudo-random number generator) */ /*********************************************************************** * This code is part of GLPK (GNU Linear Programming Kit). * * This code is a modified version of the module GB_FLIP, a portable * pseudo-random number generator. The original version of GB_FLIP is * a part of The Stanford GraphBase developed by Donald E. Knuth (see * http://www-cs-staff.stanford.edu/~knuth/sgb.html). * * Note that all changes concern only external names, so this modified * version produces exactly the same results as the original version. * * Changes were made by Andrew Makhorin . * * GLPK is free software: you can redistribute it and/or modify it * under the terms of the GNU General Public License as published by * the Free Software Foundation, either version 3 of the License, or * (at your option) any later version. * * GLPK is distributed in the hope that it will be useful, but WITHOUT * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY * or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public * License for more details. * * You should have received a copy of the GNU General Public License * along with GLPK. If not, see . ***********************************************************************/ #include "env.h" #include "rng.h" #if 0 int A[56] = { -1 }; #else #define A (rand->A) #endif /* pseudo-random values */ #if 0 int *fptr = A; #else #define fptr (rand->fptr) #endif /* the next A value to be exported */ #define mod_diff(x, y) (((x) - (y)) & 0x7FFFFFFF) /* difference modulo 2^31 */ static int flip_cycle(RNG *rand) { /* this is an auxiliary routine to do 55 more steps of the basic * recurrence, at high speed, and to reset fptr */ int *ii, *jj; for (ii = &A[1], jj = &A[32]; jj <= &A[55]; ii++, jj++) *ii = mod_diff(*ii, *jj); for (jj = &A[1]; ii <= &A[55]; ii++, jj++) *ii = mod_diff(*ii, *jj); fptr = &A[54]; return A[55]; } /*********************************************************************** * NAME * * rng_create_rand - create pseudo-random number generator * * SYNOPSIS * * #include "rng.h" * RNG *rng_create_rand(void); * * DESCRIPTION * * The routine rng_create_rand creates and initializes a pseudo-random * number generator. * * RETURNS * * The routine returns a pointer to the generator created. */ RNG *rng_create_rand(void) { RNG *rand; int i; rand = talloc(1, RNG); A[0] = -1; for (i = 1; i <= 55; i++) A[i] = 0; fptr = A; rng_init_rand(rand, 1); return rand; } /*********************************************************************** * NAME * * rng_init_rand - initialize pseudo-random number generator * * SYNOPSIS * * #include "rng.h" * void rng_init_rand(RNG *rand, int seed); * * DESCRIPTION * * The routine rng_init_rand initializes the pseudo-random number * generator. The parameter seed may be any integer number. Note that * on creating the generator this routine is called with the parameter * seed equal to 1. */ void rng_init_rand(RNG *rand, int seed) { int i; int prev = seed, next = 1; seed = prev = mod_diff(prev, 0); A[55] = prev; for (i = 21; i; i = (i + 21) % 55) { A[i] = next; next = mod_diff(prev, next); if (seed & 1) seed = 0x40000000 + (seed >> 1); else seed >>= 1; next = mod_diff(next, seed); prev = A[i]; } flip_cycle(rand); flip_cycle(rand); flip_cycle(rand); flip_cycle(rand); flip_cycle(rand); return; } /*********************************************************************** * NAME * * rng_next_rand - obtain pseudo-random integer in the range [0, 2^31-1] * * SYNOPSIS * * #include "rng.h" * int rng_next_rand(RNG *rand); * * RETURNS * * The routine rng_next_rand returns a next pseudo-random integer which * is uniformly distributed between 0 and 2^31-1, inclusive. The period * length of the generated numbers is 2^85 - 2^30. The low order bits of * the generated numbers are just as random as the high-order bits. */ int rng_next_rand(RNG *rand) { return *fptr >= 0 ? *fptr-- : flip_cycle(rand); } /*********************************************************************** * NAME * * rng_unif_rand - obtain pseudo-random integer in the range [0, m-1] * * SYNOPSIS * * #include "rng.h" * int rng_unif_rand(RNG *rand, int m); * * RETURNS * * The routine rng_unif_rand returns a next pseudo-random integer which * is uniformly distributed between 0 and m-1, inclusive, where m is any * positive integer less than 2^31. */ #define two_to_the_31 ((unsigned int)0x80000000) int rng_unif_rand(RNG *rand, int m) { unsigned int t = two_to_the_31 - (two_to_the_31 % m); int r; xassert(m > 0); do { r = rng_next_rand(rand); } while (t <= (unsigned int)r); return r % m; } /*********************************************************************** * NAME * * rng_delete_rand - delete pseudo-random number generator * * SYNOPSIS * * #include "rng.h" * void rng_delete_rand(RNG *rand); * * DESCRIPTION * * The routine rng_delete_rand frees all the memory allocated to the * specified pseudo-random number generator. */ void rng_delete_rand(RNG *rand) { tfree(rand); return; } /**********************************************************************/ #ifdef GLP_TEST /* To be sure that this modified version produces the same results as * the original version, run this validation program. */ int main(void) { RNG *rand; int j; rand = rng_create_rand(); rng_init_rand(rand, -314159); if (rng_next_rand(rand) != 119318998) { fprintf(stderr, "Failure on the first try!\n"); return -1; } for (j = 1; j <= 133; j++) rng_next_rand(rand); if (rng_unif_rand(rand, 0x55555555) != 748103812) { fprintf(stderr, "Failure on the second try!\n"); return -2; } fprintf(stderr, "OK, the random-number generator routines seem to" " work!\n"); rng_delete_rand(rand); return 0; } #endif /* eof */