#define _USE_MATH_DEFINES

#include<stdio.h>
#include<math.h>
#include<stdlib.h>

#define LENGTH 512 /* 信号長N ただし，2の整数乗 */

/* プロトタイプ宣言 */
double calcAmpPower(short *x, int N);
void applyWindow(short *x, int N);

int main(int argc, char *argv[]) {
    /* 信号長 */
    int N = LENGTH;

    double beforePower, afterPower;

    int i;

    FILE *fp = NULL;
    if (argc > 1) {
        fp = fopen(argv[1], "rb");
        if (fp == NULL) {
            fprintf(stderr, "File open error (%s)\n", argv[1]);
            exit(1);
        }
    } else {
        fprintf(stderr, "Usage: %s input-filename\n", argv[0]);
        exit(1);
    }

    /* 入力信号配列 */
    short input[LENGTH];

    /* 音声データを読み込み */
    if (fread(input, sizeof(short), N, fp) != (size_t)N) {
        fprintf(stderr, "File read error (%s)\n", argv[1]);
        fclose(fp);
        exit(1);
    }

    beforePower = calcAmpPower(input, N);

    applyWindow(input, N);

    afterPower = calcAmpPower(input, N);

    printf("BEFORE : %16f\n", beforePower);
    printf("AFTER  : %16f\n", afterPower);
    printf("DIFF   : %16f\n", beforePower - afterPower);
    printf("RATIO  : %16f\n", afterPower / beforePower);

    fclose(fp);

    return 0;
}

/* short型配列の平均パワーを求める関数 */
double calcAmpPower(short *x, int N) {
    double amp;
    double power = 0.0;
    for (int i = 0; i < N; i++) {
        amp = x[i] * x[i];
        power += amp;
    }
    return power / N;
}

/* 配列にハニング窓を適用 */
void applyWindow(short *x, int N) {
    for (int i = 0; i < N; i++) {
        double w = 0.5 - 0.5 * cos(2 * M_PI * i / (N - 1)); // ハニング窓
        x[i] *= w;
    }
}