#include <stdio.h>

#define FRAME		180
short int h[19] = {
	399,-296,-945,-1555,
	-1503,-285,2112,5061,
	7503,8450,7503,5061,
	2112,-285,-1503,-1555,
	-945,-296,399
};
static short int nBuff[FRAME + 20];
void LowpassFilter(short int nIn[],short int nOut[],int nLen,short int h[]);
void main()
{
	FILE *m_pInput;
	FILE *m_pOutput;
    short int input[FRAME];
	short int output[FRAME];
	int count;

	// 打開輸入文件
	if((m_pInput = fopen("input.wav", "rb")) == NULL) 
	{
		return;
	}
	//打開輸出文件
	if((m_pOutput = fopen("output.wav", "wb")) == NULL) 
	{
		return;
	}
    count = 0;
	while( fread(&input[0], sizeof(short int), FRAME, m_pInput) == FRAME)
	{
		printf("Frame =%d\r", count++);
		//濾波處理
		LowpassFilter(input,output,19,h);
		//將濾波后的數據寫到文件里
		fwrite(output, sizeof(short int), FRAME, m_pOutput);
	}
	fclose(m_pOutput);
	fclose(m_pInput);
}
void LowpassFilter(short int nIn[],short int nOut[],int nLen,short int h[])
{
	short int i,j;
	int sum;
	//緩沖區的內容更新
	for(i = 0;i < FRAME;i++)
	{
        nBuff[i + nLen -1] = nIn[i];
	}
	//FIR濾波處理
	for(i = 0;i < FRAME;i++)
	{
		sum = 0;
		for(j = 0;j < nLen;j++)
		{
			sum += h[j] * nBuff[i - j + nLen -1];
		}
		nOut[i] = sum >> 15;
	}
	//更新緩沖區的內容
	for(i = 0;i < nLen - 1;i++)
	{
		nBuff[nLen - i - 2] = nIn[FRAME - i - 1];
	}
}