d_random.c

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#include <math.h>
#include "d_lpc10.h"

/**********************************************************/
/* Pseudo random number generator based on Knuth, Vol 2, p. 27.
Returns INT16 variable, uniformly distributed over -32768 to 32767 */

#define MIDTAP 1
#define MAXTAP 4

INT16 Rrandom( VOID )
{
    INT16 the_random;
    static INT16 y[MAXTAP + 1] =
        {-21161, -8478, 30892, -10216, 16950};
    static INDEX j = MIDTAP;
    static INDEX k = MAXTAP;

/* The following is a 16 bit 2's complement addition,
   with overflow checking disabled */

    y[k] += y[j];
/*
    if (y[k] > 32767)
        y[k] = -(32768 - (y[k] & 32767));
    if (y[k] < -32768)
        y[k] = y[k] & 32767;
*/

    the_random = y[k];

    if (!k)
        k = MAXTAP;
    else
        k--;

    if (!j)
        j = MAXTAP;
    else
        j--;

    return the_random;
}

/**********************************************************/

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