104 lines
3 KiB
C
104 lines
3 KiB
C
/*
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* Copyright (c) 2005, Swedish Institute of Computer Science
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* All rights reserved.
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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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* 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 the
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* documentation and/or other materials provided with the distribution.
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* 3. Neither the name of the Institute nor the names of its contributors
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* may be 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 INSTITUTE AND CONTRIBUTORS ``AS IS'' AND
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* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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* ARE DISCLAIMED. IN NO EVENT SHALL THE INSTITUTE OR CONTRIBUTORS BE LIABLE
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* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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* SUCH DAMAGE.
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*
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* This file is part of the Contiki operating system.
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*
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* @(#)$Id: rand.c,v 1.7 2007/07/03 13:26:00 bg- Exp $
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*/
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#include <stdlib.h>
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#if defined(__GNUC__) && defined(__MSP430__)
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#undef RAND_MAX /* Broken header files! */
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#endif
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#include "lib/assert.h"
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#ifdef RAND_MAX
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/* Use rand() from libc if this breaks! */
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CTASSERT(RAND_MAX == 0x7fff);
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#endif
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#include "rand.h"
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/*
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* Minimal standard random number generator.
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*
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* Simple crappy ANSI C compatible random number generator that is
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* good enough for us!
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*
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* Park, S.K. and K.W. Miller, 1988;
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* Random Number Generators: Good Ones are Hard to Find,
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* Comm. of the ACM, V. 31. No. 10, pp 1192-1201
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*/
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/*
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* When possible, keep rand_state across reboots.
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*/
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#ifdef __GNUC__
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int32_t rand_state __attribute__((section(".noinit")));
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#else
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int32_t rand_state = 1;
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#endif
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int
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rand(void)
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{
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uint32_t hi, lo;
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/*
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* Perform two 16x16 bits multiplication with 32 bit results.
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*/
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lo = 16807ul * (uint16_t)(rand_state);
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hi = 16807ul * (uint16_t)(rand_state >> 16);
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lo += (hi & 0x7fff) << 16;
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/*
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* lo += hi >> 15; But faster using 16 bit registers.
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*/
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hi <<= 1;
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lo += (uint16_t)(hi >> 16);
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if ((int32_t)lo <= 0) /* Deal with rand_state == 0. */
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lo -= 0x7fffffff;
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rand_state = lo;
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if (sizeof(int) == sizeof(int16_t))
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return (lo ^ (lo >> 16)) & RAND_MAX; /* Not ANSI C! */
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else
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return lo & RAND_MAX;
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}
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void
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srand(unsigned int seed)
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{
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rand_state = seed;
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}
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