/**************************************************************************** * libs/libc/stdlib/lib_srand.c * * Copyright (C) 2007, 2011, 2016 Gregory Nutt. All rights reserved. * Author: Gregory Nutt * * Redistribution and use in source and binary forms, with or without * modification, are permitted provided that the following conditions * are met: * * 1. Redistributions of source code must retain the above copyright * notice, this list of conditions and the following disclaimer. * 2. Redistributions in binary form must reproduce the above copyright * notice, this list of conditions and the following disclaimer in * the documentation and/or other materials provided with the * distribution. * 3. Neither the name NuttX nor the names of its contributors may be * used to endorse or promote products derived from this software * without specific prior written permission. * * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE * POSSIBILITY OF SUCH DAMAGE. * ****************************************************************************/ /**************************************************************************** * Included Files ****************************************************************************/ #include #include #include #include /**************************************************************************** * Pre-processor Definitions ****************************************************************************/ /* First, second, and thired order congruential generators are supported */ #ifndef CONFIG_LIB_RAND_ORDER # define CONFIG_LIB_RAND_ORDER 1 #endif #if CONFIG_LIB_RAND_ORDER > 3 # undef CONFIG_LIB_RAND_ORDER # define CONFIG_LIB_RAND_ORDER 3 #endif /* Values needed by the random number generator */ #define RND1_CONSTK 470001 #define RND1_CONSTP 999563 #define RND2_CONSTK1 366528 #define RND2_CONSTK2 508531 #define RND2_CONSTP 998917 #define RND3_CONSTK1 360137 #define RND3_CONSTK2 519815 #define RND3_CONSTK3 616087 #define RND3_CONSTP 997783 /**************************************************************************** * Private Function Prototypes ****************************************************************************/ /* First order congruential generators */ static inline unsigned long fgenerate1(void); #if (CONFIG_LIB_RAND_ORDER == 1) static double_t frand1(void); #endif /* Second order congruential generators */ #if (CONFIG_LIB_RAND_ORDER > 1) static inline unsigned long fgenerate2(void); #if (CONFIG_LIB_RAND_ORDER == 2) static double_t frand2(void); #endif /* Third order congruential generators */ #if (CONFIG_LIB_RAND_ORDER > 2) static inline unsigned long fgenerate3(void); static double_t frand3(void); #endif #endif /**************************************************************************** * Private Data ****************************************************************************/ static unsigned long g_randint1; #if (CONFIG_LIB_RAND_ORDER > 1) static unsigned long g_randint2; #if (CONFIG_LIB_RAND_ORDER > 2) static unsigned long g_randint3; #endif #endif /**************************************************************************** * Private Functions ****************************************************************************/ /* First order congruential generators */ static inline unsigned long fgenerate1(void) { unsigned long randint; /* First order congruential generator. One may be added to the result of the * generated value to avoid the value zero. This would be fatal for the * first order random number generator. */ randint = (RND1_CONSTK * g_randint1) % RND1_CONSTP; g_randint1 = (randint == 0 ? 1 : randint); return randint; } #if (CONFIG_LIB_RAND_ORDER == 1) static double_t frand1(void) { /* First order congruential generator. */ unsigned long randint = fgenerate1(); /* Construct an floating point value in the range from 0.0 up to 1.0 */ return ((double_t)randint) / ((double_t)RND1_CONSTP); } #endif /* Second order congruential generators */ #if (CONFIG_LIB_RAND_ORDER > 1) static inline unsigned long fgenerate2(void) { unsigned long randint; /* Second order congruential generator. */ randint = (RND2_CONSTK1 * g_randint1 + RND2_CONSTK2 * g_randint2) % RND2_CONSTP; g_randint2 = g_randint1; g_randint1 = randint; /* We cannot permit both values to become zero. That would be fatal for the * second order random number generator. */ if (g_randint2 == 0 && g_randint1 == 0) { g_randint2 = 1; } return randint; } #if (CONFIG_LIB_RAND_ORDER == 2) static double_t frand2(void) { /* Second order congruential generator */ unsigned long randint = fgenerate2(); /* Construct an floating point value in the range from 0.0 up to 1.0 */ return ((double_t)randint) / ((double_t)RND2_CONSTP); } #endif /* Third order congruential generators */ #if (CONFIG_LIB_RAND_ORDER > 2) static inline unsigned long fgenerate3(void) { unsigned long randint; /* Third order congruential generator. */ randint = (RND3_CONSTK1 * g_randint1 + RND3_CONSTK2 * g_randint2 + RND3_CONSTK2 * g_randint3) % RND3_CONSTP; g_randint3 = g_randint2; g_randint2 = g_randint1; g_randint1 = randint; /* We cannot permit all three values to become zero. That would be fatal for the * third order random number generator. */ if (g_randint3 == 0 && g_randint2 == 0 && g_randint1 == 0) { g_randint3 = 1; } return randint; } static double_t frand3(void) { /* Third order congruential generator */ unsigned long randint = fgenerate3(); /* Construct an floating point value in the range from 0.0 up to 1.0 */ return ((double_t)randint) / ((double_t)RND3_CONSTP); } #endif #endif /**************************************************************************** * Public Functions ****************************************************************************/ /**************************************************************************** * Name: srand * * Description: * Seed the congruential random number generator. * ****************************************************************************/ void srand(unsigned int seed) { g_randint1 = seed; #if (CONFIG_LIB_RAND_ORDER > 1) g_randint2 = seed; fgenerate1(); #if (CONFIG_LIB_RAND_ORDER > 2) g_randint3 = seed; fgenerate2(); #endif #endif } /**************************************************************************** * Name: nrand * * Description: * Return a random, unsigned long value in the range of 0 to (limit - 1) * ****************************************************************************/ unsigned long nrand(unsigned long limit) { unsigned long result; double_t ratio; /* Loop to be sure a legal random number is generated */ do { /* Get a random integer in the range 0.0 - 1.0 */ #if (CONFIG_LIB_RAND_ORDER == 1) ratio = frand1(); #elif (CONFIG_LIB_RAND_ORDER == 2) ratio = frand2(); #else /* if (CONFIG_LIB_RAND_ORDER > 2) */ ratio = frand3(); #endif /* Then, produce the return-able value in the requested range */ result = (unsigned long)(((double_t)limit) * ratio); /* Loop because there is an (unlikely) possibility that rounding * could increase the result at the limit value about the limit. */ } while (result >= limit); return result; }