#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <io.h>

signed char IndexTable[16] = 
{
	-1,-1,-1,-1,2,4,6,8,-1,-1,-1,-1,2,4,6,8
};

short StepSizeTable[89] = 
{
	7, 8, 9, 10, 11, 12, 13, 14, 16, 17,
	19, 21, 23, 25, 28, 31, 34, 37, 41, 45,
	50, 55, 60, 66, 73, 80, 88, 97, 107, 118,
	130, 143, 157, 173, 190, 209, 230, 253, 279, 307,
	337, 371, 408, 449, 494, 544, 598, 658, 724, 796,
	876, 963, 1060, 1166, 1282, 1411, 1552, 1707, 1878, 2066,
	2272, 2499, 2749, 3024, 3327, 3660, 4026, 4428, 4871, 5358,
	5894, 6484, 7132, 7845, 8630, 9493, 10442, 11487, 12635, 13899,
	15289, 16818, 18500, 20350, 22385, 24623, 27086, 29794, 32767
};

short sample;
long prevsample; 
long previndex;

unsigned char ADPCMEncoder(short sample , long prevsample, long previndex)
{
	unsigned char code;		
	long diff;		
	long step;		
	long predsample;		
	long diffq;		
	long index;	
	long tempstep;

	/* Restore previous values of predicted sample and quantizer step
	   size index
	*/
	predsample = prevsample;
	index = previndex;
	step = StepSizeTable[index];


	/* Compute the difference between the acutal sample (sample) and the
	   the predicted sample (predsample)
	*/
	diff = sample - predsample;
	if(diff >= 0) code = 0;
	
	else
	{
		code = 8;
		diff = -diff;
	}

	/* Quantize the difference into the 4-bit ADPCM code using the
	   the quantizer step size
	*/

	tempstep = step;
	if(diff >= tempstep)
	{
      code = (code | 4);
      diff = diff - tempstep;
	}
  
    tempstep = tempstep/2;
    if(diff >= tempstep)
	{    
		code = (code | 2);
		diff = diff-tempstep;
	}

    tempstep = tempstep/2;
    if(diff >= tempstep) 
	{
		code = (code | 1);
	}


	/* Inverse quantize the ADPCM code into a predicted difference
	   using the quantizer step size
	*/
	diffq = step >> 3;

	if (code & 4) diffq = diffq + step;

    if (code & 2) diffq = diffq + step/2;

    if (code & 1) diffq = diffq + step/4;
 
    if (code & 8) predsample = predsample - diffq;
   
	else predsample = predsample + diffq;
 
	/* Fixed predictor computes new predicted sample by adding the
	   old predicted sample to predicted difference
	*/
	if(code & 8)
		predsample -= diffq;
	else
		predsample += diffq;

	/* Check for overflow of the new predicted sample
	*/
	if(predsample > 32767) predsample = 32767;
	else if(predsample < -32768) predsample = -32768;

	/* Find new quantizer stepsize index by adding the old index
	   to a table lookup using the ADPCM code
	*/
	index += IndexTable[ code];

	/* Check for overflow of the new quantizer step size index
	*/
	if(index < 0) index = 0;
	if(index > 88) index = 88;

	/* Save the predicted sample and quantizer step size index for
	   next iteration
	*/
	prevsample = (short)(predsample);
	previndex = index;

	/* Return the new ADPCM code
	*/
	return (code & 0x0f);
}

void main(int argc, char **argv)
{
	FILE *infile, *tempout, *outfile;
	int i, j;
	int inhandle;
	int fileindex = 0; 
	int filesize;
	char newname[11] = "file";
	char number[3];
	unsigned char code;
	
	// Check for at least one input file
	if (argc < 2) 	  
	{
		printf("Command line parameters incorrect. Please specify at least one audio file to encode.\n"); 
		return;
 	}

	// Compress audio files
	for (i = 1; i <= (argc - 1); i++)
	{
		// Open input file 
		if ((infile = fopen(argv[i],"r")) == NULL) 
		{			
			printf("Cannot open %s.\n", argv[i]);
			return;
		}

		// Open temp output file
		if ((tempout = fopen("tempout.adp","w")) == NULL) 
		{			
			printf("Cannot open temporary output file.\n");
			return;
		}

		inhandle = fileno(infile);
		filesize = filelength(inhandle);

		for (j = 0; j <= (filesize/4); j++)
		{
			fread(&sample, sizeof(short), 1, infile); // Read first sample
			code = ADPCMEncoder(sample, prevsample, previndex);	// Encode sample into lower nibble of code
			code = (code << 4) & 0xf0;	// Move ADPCM code to upper nibble
			
			// If odd number of samples, do not wait for second nibble of last byte
			if((j == (filesize/4)) && ((filesize/2)%2 != 0))	
			{
				fwrite(&code, sizeof(unsigned char), 1, tempout);
				break;
			}
			
			fread(&sample, sizeof(short), 1, infile); // Read second sample
			code |= ADPCMEncoder(sample, prevsample, previndex);	// Encode sample and save in lower nibble of code
			fwrite(&code, sizeof(unsigned char), 1, tempout);	// Write code to file
		}

		fclose(infile);
		fclose(tempout);
	
		itoa(i, number, 10);

		strcat(newname, number);
		strcat(newname, ".adp");
		rename("tempout.adp", newname);
		remove("tempout.adp");
	}