#include <math.h>
#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>
#include <string.h>
#include <time.h>

#define BUF_SIZE 1211

static int16_t buf[BUF_SIZE];
static const int16_t a_sin = 2048;
static const int fs = 200e3;        /* sampling rate, samples/sec */
static const int16_t dc = 100;
static const double k_sin_avg = 0.637;  /* A_avg/A_peak for sine wave */

/**
 * Calculate the magnitude of sine wave signal (generated internally).
 *
 * @param f_sin Sine wave frequency, Hz
 * @param theta Start phase, radians
 *
 * @return Calculated A_peak
 */
int calc(int f_sin, double theta)
{
    size_t n;
    double sum = 0;
    double ppp;         /* points per period */
    double fp;          /* full periods in buffer */
    size_t poi;         /* number of points of interest */
    int a_avg, a_peak;

    for (n = 0; n < BUF_SIZE; ++n)
        buf[n] = dc + a_sin * (1 + sin(2*M_PI*f_sin/fs * n + theta));

    /* Remove DC component first (using MEAN_BUF in fw) */
    for (n = 0; n < BUF_SIZE; ++n)
        buf[n] -= dc + a_sin;

    /* Calculate samples number for whole periods in the buffer */
    ppp = fs/f_sin;
    fp = floor((double)BUF_SIZE / ppp);
    poi = round(fp * ppp);

    /* Calculate the average and peak magnitude */
    for (n = 0; n < poi; ++n)
        sum += abs(buf[n]);
    a_avg = round(sum / poi);
    a_peak = round(a_avg / k_sin_avg);

    return a_peak;
}

int main(void)
{
    int f;

    srand(time(0));
    for (f = 3000; f < 20000; ++f) {
        int a_peak;
        double err;

        a_peak = calc(f, rand());
        err = fabs(a_sin - a_peak) / a_sin * 100;
        if (err >= 1)
            printf("%d,%f\n", f, err);
    }

    return EXIT_SUCCESS;
}