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/*********************************************************** 
Copyright 1992 by Stichting Mathematisch Centrum, Amsterdam, The 
Netherlands. 
 
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******************************************************************/ 
 
/* 
** Intel/DVI ADPCM coder/decoder. 
** 
** The algorithm for this coder was taken from the IMA Compatibility Project 
** proceedings, Vol 2, Number 2; May 1992. 
** 
** Version 1.2, 18-Dec-92. 
** 
** Change log: 
 
	Modified by John Walker in September 1995 for use in 
	Speak Freely.  The only change was to make the encoder 
	and decoder work directly on u-law encoded samples. 
	This permits splicing it into the compression chain 
	at the proper point, after possible 2X compression has 
	been performed. 
 
** - Fixed a stupid bug, where the delta was computed as 
**	 stepsize*code/4 in stead of stepsize*(code+0.5)/4. 
** - There was an off-by-one error causing it to pick 
**	 an incorrect delta once in a blue moon. 
** - The NODIVMUL define has been removed. Computations are now always done 
**	 using shifts, adds and subtracts. It turned out that, because the standard 
**	 is defined using shift/add/subtract, you needed bits of fixup code 
**	 (because the div/mul simulation using shift/add/sub made some rounding 
**   errors that real div/mul don't make) and all together the resultant code 
**	 ran slower than just using the shifts all the time. 
** - Changed some of the variable names to be more meaningful. 
*/ 
 
#include <windows.h> 
 
#include "adpcm_u.h" 
#include "../ulaw.h" 
 
#ifndef __STDC__ 
#define signed 
#endif 
 
/* Intel ADPCM step variation table */ 
static int indexTable[16] = { 
	-1, -1, -1, -1, 2, 4, 6, 8, 
	-1, -1, -1, -1, 2, 4, 6, 8, 
}; 
 
static int 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 
}; 
	 
void 
adpcm_coder_u(indata, outdata, len, state) 
	unsigned char indata[]; 
	char outdata[]; 
	int len; 
	struct adpcm_state *state; 
{ 
	unsigned char *inp; 		/* Input buffer pointer */ 
	signed char *outp;			/* output buffer pointer */ 
	int val;					/* Current input sample value */ 
	int sign;					/* Current adpcm sign bit */ 
	int delta;					/* Current adpcm output value */ 
	long diff;					/* Difference between val and valprev */ 
	int step;					/* Stepsize */ 
	long valpred;				/* Predicted output value */ 
	int vpdiff; 				/* Current change to valpred */ 
	int index;					/* Current step change index */ 
	int outputbuffer;			/* place to keep previous 4-bit value */ 
	int bufferstep; 			/* toggle between outputbuffer/output */ 
 
	outp = (signed char *)outdata; 
	inp = indata; 
 
	valpred = state->valprev; 
	index = state->index; 
	step = stepsizeTable[index]; 
	 
	bufferstep = 1; 
 
	for ( ; len > 0 ; len-- ) { 
		val = audio_u2s(*inp++); 
 
		/* Step 1 - compute difference with previous value */ 
		diff = val - valpred; 
		sign = (diff < 0) ? 8 : 0; 
		if ( sign ) diff = (-diff); 
 
		/* Step 2 - Divide and clamp */ 
		/* Note: 
		** This code *approximately* computes: 
		**	  delta = diff*4/step; 
		**	  vpdiff = (delta+0.5)*step/4; 
		** but in shift step bits are dropped. The net result of this is 
		** that even if you have fast mul/div hardware you cannot put it to 
		** good use since the fixup would be too expensive. 
		*/ 
		delta = 0; 
		vpdiff = (step >> 3); 
		 
		if ( diff >= step ) { 
			delta = 4; 
			diff -= step; 
			vpdiff += step; 
		} 
		step >>= 1; 
		if ( diff >= step  ) { 
			delta |= 2; 
			diff -= step; 
			vpdiff += step; 
		} 
		step >>= 1; 
		if ( diff >= step ) { 
			delta |= 1; 
			vpdiff += step; 
		} 
 
		/* Step 3 - Update previous value */ 
		if ( sign ) 
		  valpred -= vpdiff; 
		else 
		  valpred += vpdiff; 
 
		/* Step 4 - Clamp previous value to 16 bits */ 
		if ( valpred > 32767L ) 
		  valpred = 32767L; 
		else if ( valpred < -32768L ) 
		  valpred = -32768L; 
 
		/* Step 5 - Assemble value, update index and step values */ 
		delta |= sign; 
		 
		index += indexTable[delta]; 
		if ( index < 0 ) index = 0; 
		if ( index > 88 ) index = 88; 
		step = stepsizeTable[index]; 
 
		/* Step 6 - Output value */ 
		if ( bufferstep ) { 
			outputbuffer = (delta << 4) & 0xf0; 
		} else { 
			*outp++ = (delta & 0x0f) | outputbuffer; 
		} 
		bufferstep = !bufferstep; 
	} 
 
	/* Output last step, if needed */ 
	if ( !bufferstep ) 
	  *outp++ = outputbuffer; 
	 
	state->valprev = (short) valpred; 
	state->index = index; 
} 
 
void 
adpcm_decoder_u(indata, outdata, len, state) 
	char indata[]; 
	unsigned char outdata[]; 
	int len; 
	struct adpcm_state *state; 
{ 
	signed char *inp;			/* Input buffer pointer */ 
	unsigned char *outp;		/* Output buffer pointer */ 
	int sign;					/* Current adpcm sign bit */ 
	int delta;					/* Current adpcm output value */ 
	int step;					/* Stepsize */ 
	long valpred;				/* Predicted value */ 
	int vpdiff; 				/* Current change to valpred */ 
	int index;					/* Current step change index */ 
	int inputbuffer;			/* place to keep next 4-bit value */ 
	int bufferstep; 			/* toggle between inputbuffer/input */ 
 
	outp = outdata; 
	inp = (signed char *)indata; 
 
	valpred = state->valprev; 
	index = state->index; 
	step = stepsizeTable[index]; 
 
	bufferstep = 0; 
	 
	for ( ; len > 0 ; len-- ) { 
		 
		/* Step 1 - get the delta value */ 
		if ( bufferstep ) { 
			delta = inputbuffer & 0xf; 
		} else { 
			inputbuffer = *inp++; 
			delta = (inputbuffer >> 4) & 0xf; 
		} 
		bufferstep = !bufferstep; 
 
		/* Step 2 - Find new index value (for later) */ 
		index += indexTable[delta]; 
		if ( index < 0 ) index = 0; 
		if ( index > 88 ) index = 88; 
 
		/* Step 3 - Separate sign and magnitude */ 
		sign = delta & 8; 
		delta = delta & 7; 
 
		/* Step 4 - Compute difference and new predicted value */ 
		/* 
        ** Computes 'vpdiff = (delta+0.5)*step/4', but see comment 
		** in adpcm_coder. 
		*/ 
		vpdiff = step >> 3; 
		if ( delta & 4 ) vpdiff += step; 
		if ( delta & 2 ) vpdiff += step>>1; 
		if ( delta & 1 ) vpdiff += step>>2; 
 
		if ( sign ) 
		  valpred -= vpdiff; 
		else 
		  valpred += vpdiff; 
 
		/* Step 5 - clamp output value */ 
		if ( valpred > 32767L ) 
		  valpred = 32767L; 
		else if ( valpred < -32768L ) 
		  valpred = -32768L; 
 
		/* Step 6 - Update step value */ 
		step = stepsizeTable[index]; 
 
		/* Step 7 - Output value */ 
		*outp++ = audio_s2u(valpred); 
	} 
 
	state->valprev = (short) valpred; 
	state->index = index; 
}