278 lines
7.6 KiB
C
278 lines
7.6 KiB
C
/****************************************************************************
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* libc/stdlib/lib_rand.c
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*
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* Copyright (C) 2007, 2011 Gregory Nutt. All rights reserved.
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* Author: Gregory Nutt <gnutt@nuttx.org>
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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*
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in
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* the documentation and/or other materials provided with the
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* distribution.
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* 3. Neither the name NuttX nor the names of its contributors may be
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* used to endorse or promote products derived from this software
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* without specific prior written permission.
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*
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* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
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* FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
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* COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
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* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
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* BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
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* OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
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* AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
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* ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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* POSSIBILITY OF SUCH DAMAGE.
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*
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****************************************************************************/
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/****************************************************************************
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* Included Files
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****************************************************************************/
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#include <sys/types.h>
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#include <stdlib.h>
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/****************************************************************************
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* Pre-processor Definitions
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****************************************************************************/
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/* First, second, and thired order congruential generators are supported */
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#ifndef CONFIG_LIB_RAND_ORDER
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# define CONFIG_LIB_RAND_ORDER 1
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#endif
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#if CONFIG_LIB_RAND_ORDER > 3
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# undef CONFIG_LIB_RAND_ORDER
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# define CONFIG_LIB_RAND_ORDER 3
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#endif
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/* Values needed by the random number generator */
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#define RND1_CONSTK 470001
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#define RND1_CONSTP 999563
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#define RND2_CONSTK1 366528
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#define RND2_CONSTK2 508531
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#define RND2_CONSTP 998917
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#define RND3_CONSTK1 360137
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#define RND3_CONSTK2 519815
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#define RND3_CONSTK3 616087
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#define RND3_CONSTP 997783
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/****************************************************************************
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* Private Function Prototypes
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****************************************************************************/
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static unsigned int nrand(unsigned int nLimit);
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/* First order congruential generators */
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static inline unsigned long fgenerate1(void);
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#if (CONFIG_LIB_RAND_ORDER == 1)
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static double_t frand1(void);
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#endif
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/* Second order congruential generators */
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#if (CONFIG_LIB_RAND_ORDER > 1)
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static inline unsigned long fgenerate2(void);
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#if (CONFIG_LIB_RAND_ORDER == 2)
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static double_t frand2(void);
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#endif
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/* Third order congruential generators */
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#if (CONFIG_LIB_RAND_ORDER > 2)
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static inline unsigned long fgenerate3(void);
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static double_t frand3(void);
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#endif
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#endif
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/****************************************************************************
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* Private Data
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****************************************************************************/
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static unsigned long g_randint1;
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#if (CONFIG_LIB_RAND_ORDER > 1)
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static unsigned long g_randint2;
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#if (CONFIG_LIB_RAND_ORDER > 2)
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static unsigned long g_randint3;
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#endif
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#endif
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/****************************************************************************
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* Private Functions
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****************************************************************************/
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static unsigned int nrand(unsigned int nLimit)
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{
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unsigned long result;
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double_t ratio;
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/* Loop to be sure a legal random number is generated */
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do
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{
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/* Get a random integer in the requested range */
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#if (CONFIG_LIB_RAND_ORDER == 1)
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ratio = frand1();
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#elif (CONFIG_LIB_RAND_ORDER == 2)
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ratio = frand2();
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#else /* if (CONFIG_LIB_RAND_ORDER > 2) */
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ratio = frand3();
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#endif
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/* Then, produce the return-able value */
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result = (unsigned long)(((double_t)nLimit) * ratio);
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}
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while (result >= (unsigned long)nLimit);
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return (unsigned int)result;
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}
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/* First order congruential generators */
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static inline unsigned long fgenerate1(void)
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{
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unsigned long randint;
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/* First order congruential generator. One may be added to the result of the
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* generated value to avoid the value zero. This would be fatal for the
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* first order random number generator.
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*/
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randint = (RND1_CONSTK * g_randint1) % RND1_CONSTP;
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g_randint1 = (randint == 0 ? 1 : randint);
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return randint;
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}
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#if (CONFIG_LIB_RAND_ORDER == 1)
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static double_t frand1(void)
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{
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/* First order congruential generator. */
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unsigned long randint = fgenerate1();
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/* Construct an floating point value in the range from 0.0 up to 1.0 */
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return ((double_t)randint) / ((double_t)RND1_CONSTP);
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}
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#endif
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/* Second order congruential generators */
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#if (CONFIG_LIB_RAND_ORDER > 1)
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static inline unsigned long fgenerate2(void)
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{
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unsigned long randint;
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/* Second order congruential generator. */
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randint = (RND2_CONSTK1 * g_randint1 +
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RND2_CONSTK2 * g_randint2) % RND2_CONSTP;
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g_randint2 = g_randint1;
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g_randint1 = randint;
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/* We cannot permit both values to become zero. That would be fatal for the
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* second order random number generator.
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*/
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if (g_randint2 == 0 && g_randint1 == 0)
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{
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g_randint2 = 1;
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}
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return randint;
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}
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#if (CONFIG_LIB_RAND_ORDER == 2)
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static double_t frand2(void)
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{
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/* Second order congruential generator */
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unsigned long randint = fgenerate2();
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/* Construct an floating point value in the range from 0.0 up to 1.0 */
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return ((double_t)randint) / ((double_t)RND2_CONSTP);
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}
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#endif
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/* Third order congruential generators */
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#if (CONFIG_LIB_RAND_ORDER > 2)
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static inline unsigned long fgenerate3(void)
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{
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unsigned long randint;
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/* Third order congruential generator. */
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randint = (RND3_CONSTK1 * g_randint1 +
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RND3_CONSTK2 * g_randint2 +
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RND3_CONSTK2 * g_randint3) % RND3_CONSTP;
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g_randint3 = g_randint2;
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g_randint2 = g_randint1;
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g_randint1 = randint;
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/* We cannot permit all three values to become zero. That would be fatal for the
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* third order random number generator.
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*/
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if (g_randint3 == 0 && g_randint2 == 0 && g_randint1 == 0)
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{
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g_randint3 = 1;
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}
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return randint;
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}
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static double_t frand3(void)
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{
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/* Third order congruential generator */
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unsigned long randint = fgenerate3();
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/* Construct an floating point value in the range from 0.0 up to 1.0 */
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return ((double_t)randint) / ((double_t)RND3_CONSTP);
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}
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#endif
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#endif
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/****************************************************************************
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* Public Functions
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****************************************************************************/
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/****************************************************************************
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* Function: srand, rand
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****************************************************************************/
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void srand(unsigned int seed)
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{
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g_randint1 = seed;
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#if (CONFIG_LIB_RAND_ORDER > 1)
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g_randint2 = seed;
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(void)fgenerate1();
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#if (CONFIG_LIB_RAND_ORDER > 2)
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g_randint3 = seed;
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(void)fgenerate2();
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#endif
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#endif
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}
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int rand(void)
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{
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return (int)nrand(32768);
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}
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