clo_rng_lcg.cl

/*
 * This file is part of CL_Ops.
 *
 * CL_Ops is free software: you can redistribute it and/or modify
 * it under the terms of the GNU Lesser General Public License as
 * published by the Free Software Foundation, either version 3 of the
 * License, or (at your option) any later version.
 *
 * CL_Ops 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 Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with CL_Ops. If not, see
 * <http://www.gnu.org/licenses/>.
 * */

/**
 * @file
 * GPU implementation of a linear congruential pseudorandom
 * number generator (LCG), as defined by D. H. Lehmer and described by
 * Donald E. Knuth in The Art of Computer Programming, Volume 2:
 * Seminumerical Algorithms, section 3.2.1. It is a similar
 * implementation to Java Random class.
 */

/* For the LCG RNG, the size of each seed is ulong. */
typedef ulong clo_statetype;

/* Ulong is ulong... */
#define clo_ulong2statetype(seed) (seed)

/**
 * Returns the next pseudorandom value using a LCG random number
 * generator.
 *
 * @param[in,out] states Array of RNG states.
 * @param[in] index Index of relevant state to use and update.
 * @return The next pseudorandom value using a LCG random number
 * generator.
 */
uint clo_rng_next(__global clo_statetype *states, uint index) {

	/* Assume 32 bits */
	uint bits = 32;

	/* Get current state */
	clo_statetype state = states[index];

	/* Update state */
	state = (state * 0x5DEECE66DL + 0xBL) & ((1L << 48) - 1);

	/* Keep state */
	states[index] = state;

	/* Return value */
	return (uint) (state >> (48 - bits));
}