arithc._h

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#ifndef ARITHC_INTERNAL_H
#define ARITHC_INTERNAL_H

/* consts from Michael Schindler */

#define CODE_BITS		31
#define SHIFT_BITS		(CODE_BITS - 8)
#define CODE_BYTES		((CODE_BITS+7)/8)

#define PRECISION_BITS	9		// coding is done to this accuracy (in terms of range>>PRECISION_BITS)

#define MinRange 		((ulong)1<<SHIFT_BITS)
#define One   			((ulong)1<<CODE_BITS)
#define CumProbMax  	(MinRange>>PRECISION_BITS)
#define CODE_MASK		(One - 1)

#define EXTRA_BITS		((CODE_BITS-1) % 8 + 1)		// == 7	== CODE_BITS - (8*(CODE_BYTES-1))
#define TAIL_EXTRA_BITS	(8 - EXTRA_BITS)			// == 1

	// extra_bits are the bits in "code" that don't quite fit in bytes

//--------------------------------------------------------------
//--- range normalizers for encoder & decoder; also does the IO

void INLINE arithEncRenorm(arithInfo * ari,ulong code,ulong range)
{
	assert( range <= One );

	while( range <= MinRange )
	{
		ulong byte;
		byte = (code >> SHIFT_BITS);
	
		if ( byte == 0xFF )
		{
			/** the waiting queue is incremented like :
			*		(ari->queue), 0xFF, 0xFF, ... ,0xFF, code
			***/

			ari->overflow_bytes++;
		}
		else
		{
			ulong carry;
			carry = code>>CODE_BITS;	

				/* carry == 1 or 0 : is the top bit on ?
				*	carry = byte>>8
				* if ( carry )	send nextbyte+1
				*				MinRange queue with zeros
				* else			send nextbyte
				*				MinRange queue with ones
				**/					
		
			*(ari->outPtr)++ = (ubyte)(ari->queue + carry);	// propagate the carry.
			// send the queue
			if ( ari->overflow_bytes )
			{
				*(ari->outPtr)++ = (ubyte)(0xFF + carry);
				while ( --(ari->overflow_bytes) ) *(ari->outPtr)++ = (ubyte)(0xFF + carry);
			}
			ari->queue = byte;
		}

		code = (code<<8) & CODE_MASK;
		range <<= 8;
	}

	assert( range <= One );

	ari->code  = code;
	ari->range = range;
}

void INLINE arithDecRenorm(arithInfo * ari,ulong *pcode,ulong *prange)
{
ulong range,code;

	range = ari->range;
	code  = ari->code;

	assert( range <= One );

	while ( range <= MinRange )
	{
		range <<= 8;
		code = (code<<8) + (((ari->queue)<<EXTRA_BITS)&0xFF);	// use the top bit in the queue
		ari->queue = *(ari->outPtr)++;
		code += (ari->queue) >> (TAIL_EXTRA_BITS);
	}
	
	assert( range <= One );

	*prange = range;
	*pcode = code;
}

#endif // ARITHC_INTERNAL_H