/* 
 * Contributor(s):
 *
 * Piotr Gregor     <piotrgregor@rsyncme.org>
 */

#ifndef __AVMD_DESA2_TWEAKED_H__
    #include "avmd_desa2_tweaked.h"
#endif

#include <switch.h>
#include <stdio.h>

#ifdef WIN32
    #include <float.h>
    #define ISNAN(x) (!!(_isnan(x)))
    #define ISINF(x) (isinf(x))
#else
    int __isnan(double);
    #define ISNAN(x) (__isnan(x))
    #define ISINF(x) (__isinf(x))
#endif

#include "avmd_buffer.h"
#include "avmd_desa2_tweaked.h"
#include "avmd_options.h"

#ifndef AVMD_FAST_MATH
    #include "avmd_fast_acosf.h"
#endif


double
avmd_desa2_tweaked(circ_buffer_t *b, size_t i, double *amplitude) {
    double n, d;
    double x0;
    double x1;
    double x2;
    double x3;
    double x4;
    double x2sq;
    double result;
    double PSI_Xn, PSI_Yn, NEEDED;

    x0 = GET_SAMPLE((b), (i));
    x1 = GET_SAMPLE((b), ((i) + 1));
    x2 = GET_SAMPLE((b), ((i) + 2));
    x3 = GET_SAMPLE((b), ((i) + 3));
    x4 = GET_SAMPLE((b), ((i) + 4));
    x2sq = x2 * x2;
    d = 2.0 * ((x2sq) - (x1 * x3));
    PSI_Xn = ((x2sq) - (x0 * x4));
    NEEDED = ((x1 * x1) - (x0 * x2)) + ((x3 * x3) - (x2 * x4));
    n = ((x2sq) - (x0 * x4)) - NEEDED;
    PSI_Yn = NEEDED + PSI_Xn;

/* instead of
#ifdef FASTMATH
    result = 0.5 * (double)fast_acosf((float)n/d);
#else
    result = 0.5 * acos(n/d);
#endif
 we do simplified, modified for speed version : */

    result = n/d;
    if (ISINF(result)) {
        *amplitude = 0.0;
        if (n < 0.0) {
            return -10.0;
        } else {
            return 10.0;
        }
    }
    *amplitude = 2.0 * PSI_Xn / sqrt(PSI_Yn);
    return result;
}
