5d09b4cbd0
refs to https://pubs.opengroup.org/onlinepubs/7908799/xsh/rand.html Signed-off-by: dongjiuzhu1 <dongjiuzhu1@xiaomi.com>
312 lines
8.4 KiB
C
312 lines
8.4 KiB
C
/****************************************************************************
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* libs/libc/stdlib/lib_srand.c
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*
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* Licensed to the Apache Software Foundation (ASF) under one or more
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* contributor license agreements. See the NOTICE file distributed with
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* this work for additional information regarding copyright ownership. The
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* ASF licenses this file to you under the Apache License, Version 2.0 (the
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* "License"); you may not use this file except in compliance with the
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* License. You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
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* WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
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* License for the specific language governing permissions and limitations
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* under the License.
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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 <nuttx/config.h>
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#include <stdlib.h>
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#include <nuttx/lib/lib.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_LIBC_RAND_ORDER
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# define CONFIG_LIBC_RAND_ORDER 1
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#endif
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#if CONFIG_LIBC_RAND_ORDER > 3
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# undef CONFIG_LIBC_RAND_ORDER
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# define CONFIG_LIBC_RAND_ORDER 3
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#endif
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#ifndef CONFIG_HAVE_DOUBLE
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typedef float float_t;
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#else
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typedef double float_t;
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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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/* First order congruential generators */
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static inline unsigned long fgenerate1(FAR unsigned long *seed);
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#if (CONFIG_LIBC_RAND_ORDER == 1)
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static float_t frand1(FAR unsigned long *seed);
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#endif
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/* Second order congruential generators */
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#if (CONFIG_LIBC_RAND_ORDER > 1)
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static inline unsigned long fgenerate2(void);
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#if (CONFIG_LIBC_RAND_ORDER == 2)
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static float_t frand2(void);
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#endif
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/* Third order congruential generators */
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#if (CONFIG_LIBC_RAND_ORDER > 2)
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static inline unsigned long fgenerate3(void);
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static float_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_LIBC_RAND_ORDER > 1)
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static unsigned long g_randint2;
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#if (CONFIG_LIBC_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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/* First order congruential generators */
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static inline unsigned long fgenerate1(FAR unsigned long *seed)
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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
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* the generated value to avoid the value zero. This would be fatal for
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* the first order random number generator.
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*/
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randint = (RND1_CONSTK * (*seed)) % RND1_CONSTP;
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*seed = (randint == 0 ? 1 : randint);
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return randint;
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}
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#if (CONFIG_LIBC_RAND_ORDER == 1)
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static float_t frand1(FAR unsigned long *seed)
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{
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/* First order congruential generator. */
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unsigned long randint = fgenerate1(seed);
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/* Construct an floating point value in the range from 0.0 up to 1.0 */
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return ((float_t)randint) / ((float_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_LIBC_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
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* the 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_LIBC_RAND_ORDER == 2)
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static float_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 ((float_t)randint) / ((float_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_LIBC_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
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* for the 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 float_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 ((float_t)randint) / ((float_t)RND3_CONSTP);
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}
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#endif
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#endif
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static unsigned long nrand_r(unsigned long limit,
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FAR unsigned long *seed)
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{
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unsigned long result;
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float_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 range 0.0 - 1.0 */
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#if (CONFIG_LIBC_RAND_ORDER == 1)
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ratio = frand1(seed);
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#elif (CONFIG_LIBC_RAND_ORDER == 2)
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ratio = frand2();
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#else /* if (CONFIG_LIBC_RAND_ORDER > 2) */
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ratio = frand3();
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#endif
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/* Then, produce the return-able value in the requested range */
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result = (unsigned long)(((float_t)limit) * ratio);
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/* Loop because there is an (unlikely) possibility that rounding
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* could increase the result at the limit value about the limit.
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*/
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}
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while (result >= limit);
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return result;
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}
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/****************************************************************************
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* Public Functions
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****************************************************************************/
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/****************************************************************************
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* Name: srand
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*
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* Description:
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* Seed the congruential random number generator.
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*
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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_LIBC_RAND_ORDER > 1)
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g_randint2 = seed;
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fgenerate1(&g_randint1);
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#if (CONFIG_LIBC_RAND_ORDER > 2)
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g_randint3 = seed;
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fgenerate2();
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#endif
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#endif
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}
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/****************************************************************************
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* Name: nrand
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*
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* Description:
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* Return a random, unsigned long value in the range of 0 to (limit - 1)
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*
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****************************************************************************/
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unsigned long nrand(unsigned long limit)
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{
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return nrand_r(limit, &g_randint1);
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}
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/****************************************************************************
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* Name: rand_r
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*
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* Description:
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* The function rand() is not reentrant, since it uses hidden state that
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* is modified on each call. This might just be the seed value to be used
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* by the next call, or it might be something more elaborate. In order to
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* get reproducible behavior in a threaded application, this state must be
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* made explicit; this can be done using the reentrant function rand_r().
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*
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* Return a random, int value in the range of 0 to INT_MAX.
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*
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****************************************************************************/
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int rand_r(FAR unsigned int *seedp)
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{
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unsigned long seed = *seedp;
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unsigned long rand;
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rand = nrand_r(INT_MAX, &seed);
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*seedp = (unsigned int)seed;
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return (int)rand;
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}
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