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* Use 16x16 bit ==> 32 bit multiplications. This gives a speedup of 5 on
the MSP430.
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parent
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@ -28,7 +28,7 @@
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*
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*
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* This file is part of the Contiki operating system.
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* This file is part of the Contiki operating system.
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*
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*
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* @(#)$Id: rand.c,v 1.6 2007/06/05 10:02:53 bg- Exp $
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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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*/
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#include <stdlib.h>
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#include <stdlib.h>
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@ -61,16 +61,39 @@ CTASSERT(RAND_MAX == 0x7fff);
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* When possible, keep rand_state across reboots.
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* When possible, keep rand_state across reboots.
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*/
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*/
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#ifdef __GNUC__
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#ifdef __GNUC__
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unsigned long rand_state __attribute__((section(".noinit")));
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int32_t rand_state __attribute__((section(".noinit")));
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#else
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#else
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unsigned long rand_state = 123459876ul;
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int32_t rand_state = 1;
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#endif
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#endif
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int
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int
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rand()
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rand(void)
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{
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{
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rand_state = (16807*rand_state) % 2147483647ul;
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uint32_t hi, lo;
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return (rand_state ^ (rand_state >> 16)) & RAND_MAX;
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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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}
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void
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void
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@ -28,10 +28,10 @@
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*
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*
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* This file is part of the Contiki operating system.
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* This file is part of the Contiki operating system.
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*
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*
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* @(#)$Id: rand.h,v 1.1 2006/06/17 22:41:18 adamdunkels Exp $
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* @(#)$Id: rand.h,v 1.2 2007/07/03 13:26:15 bg- Exp $
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*/
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*/
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/* -*- C -*- */
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/* -*- C -*- */
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/* @(#)$Id: rand.h,v 1.1 2006/06/17 22:41:18 adamdunkels Exp $ */
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/* @(#)$Id: rand.h,v 1.2 2007/07/03 13:26:15 bg- Exp $ */
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#ifndef RAND_H
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#ifndef RAND_H
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#define RAND_H
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#define RAND_H
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@ -50,7 +50,7 @@
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* Comm. of the ACM, V. 31. No. 10, pp 1192-1201
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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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extern unsigned long rand_state;
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extern int32_t rand_state;
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int rand(void);
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int rand(void);
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