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incubator-nuttx/libc/stdlib/lib_srand.c

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/****************************************************************************
* libc/stdlib/lib_srand.c
*
* Copyright (C) 2007, 2011, 2016 Gregory Nutt. All rights reserved.
* Author: Gregory Nutt <gnutt@nuttx.org>
*
* 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 <nuttx/config.h>
#include <sys/types.h>
#include <stdlib.h>
#include <nuttx/lib/lib.h>
/****************************************************************************
* 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;
(void)fgenerate1();
#if (CONFIG_LIB_RAND_ORDER > 2)
g_randint3 = seed;
(void)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 a (unlikely) possibility that round could but
* the result at the limit value.
*/
}
while (result >= limit);
return result;
}
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