contiki/core/lib/rand.c

105 lines
3.0 KiB
C

/*
* Copyright (c) 2005, Swedish Institute of Computer Science
* All rights reserved.
*
* 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 of the Institute 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 INSTITUTE 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 INSTITUTE 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.
*
* This file is part of the Contiki operating system.
*
* @(#)$Id: rand.c,v 1.9 2007/09/04 08:48:54 bg- Exp $
*/
#include <stdlib.h>
#if defined(__GNUC__) && defined(__MSP430__)
#undef RAND_MAX /* Broken header files! */
#endif
#include "contiki.h"
#include "lib/assert.h"
#ifdef RAND_MAX
/* Use rand() from libc if this breaks! */
CTASSERT(RAND_MAX == 0x7fff);
#endif
#include "rand.h"
/*
* Minimal standard random number generator.
*
* Simple crappy ANSI C compatible random number generator that is
* good enough for us!
*
* Park, S.K. and K.W. Miller, 1988;
* Random Number Generators: Good Ones are Hard to Find,
* Comm. of the ACM, V. 31. No. 10, pp 1192-1201
*/
/*
* When possible, keep rand_state across reboots.
*/
#ifdef __GNUC__
int32_t rand_state __attribute__((section(".noinit")));
#else
int32_t rand_state = 1;
#endif
int
rand(void)
{
uint32_t hi, lo;
/*
* Perform two 16x16 bits multiplication with 32 bit results.
*/
lo = 16807ul * (uint16_t)(rand_state);
hi = 16807ul * (uint16_t)(rand_state >> 16);
lo += (hi & 0x7fff) << 16;
/*
* lo += hi >> 15; But faster using 16 bit registers.
*/
hi <<= 1;
lo += (uint16_t)(hi >> 16);
if ((int32_t)lo <= 0) /* Deal with rand_state == 0. */
lo -= 0x7fffffff;
rand_state = lo;
if (sizeof(int) == sizeof(int16_t))
return (lo ^ (lo >> 16)) & RAND_MAX; /* Not ANSI C! */
else
return lo & RAND_MAX;
}
void
srand(unsigned int seed)
{
rand_state = seed;
}