polyphase.c

来自「An complete pmp solution for mattel juic」· C语言 代码 · 共 112 行

/* ***** BEGIN LICENSE BLOCK *****
 * Version: RCSL 1.0/RPSL 1.0
 *
 * Portions Copyright (c) 1995-2002 RealNetworks, Inc. All Rights Reserved.
 *
 * The contents of this file, and the files included with this file, are
 * subject to the current version of the RealNetworks Public Source License
 * Version 1.0 (the "RPSL") available at
 * http://www.helixcommunity.org/content/rpsl unless you have licensed
 * the file under the RealNetworks Community Source License Version 1.0
 * (the "RCSL") available at http://www.helixcommunity.org/content/rcsl,
 * in which case the RCSL will apply. You may also obtain the license terms
 * directly from RealNetworks.  You may not use this file except in
 * compliance with the RPSL or, if you have a valid RCSL with RealNetworks
 * applicable to this file, the RCSL.  Please see the applicable RPSL or
 * RCSL for the rights, obligations and limitations governing use of the
 * contents of the file.
 *
 * This file is part of the Helix DNA Technology. RealNetworks is the
 * developer of the Original Code and owns the copyrights in the portions
 * it created.
 *
 * This file, and the files included with this file, is distributed and made
 * available on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER
 * EXPRESS OR IMPLIED, AND REALNETWORKS HEREBY DISCLAIMS ALL SUCH WARRANTIES,
 * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY, FITNESS
 * FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT.
 *
 * Technology Compatibility Kit Test Suite(s) Location:
 *    http://www.helixcommunity.org/content/tck
 *
 * Contributor(s):
 *
 * ***** END LICENSE BLOCK ***** */

/**************************************************************************************
 * Fixed-point MP3 decoder
 * Jon Recker ([e-mail]), Ken Cooke ([e-mail])
 * June 2003
 *
 * polyphase.c - final stage of subband transform (polyphase synthesis filter)
 *
 * This is the C reference version using __int64
 * Look in the appropriate subdirectories for optimized asm implementations
 *   (e.g. arm/asmpoly.s)
 **************************************************************************************/

#include "coder.h"
#include "assembly.h"

/* input to Polyphase = Q(DQ_FRACBITS_OUT-2), gain 2 bits in convolution
 *  we also have the implicit bias of 2^15 to add back, so net fraction bits =
 *    DQ_FRACBITS_OUT - 2 - 2 - 15
 *  (see comment on Dequantize() for more info)
 */
#define DEF_NFRACBITS	(DQ_FRACBITS_OUT - 2 - 2 - 15)
#define CSHIFT	12	/* coefficients have 12 leading sign bits for early-terminating mulitplies */

static __inline i16 ClipToShort(i32 x, i32 fracBits)
{
	i32 sign;

	/* assumes you've already rounded (x += (1 << (fracBits-1))) */
	x >>= fracBits;

	/* Ken's trick: clips to [-32768, 32767] */
	sign = x >> 31;
	if (sign != (x >> 15))
		x = sign ^ ((1 << 15) - 1);

	return (i16)x;
}

#define MC0M(x)	{ \
	c1 = *coef;		coef++;		c2 = *coef;		coef++; \
	vLo = *(vb1+(x));			vHi = *(vb1+(23-(x))); \
	sum1L = MADD64(sum1L, vLo,  c1);	sum1L = MADD64(sum1L, vHi, -c2); \
}

#define MC1M(x)	{ \
	c1 = *coef;		coef++; \
	vLo = *(vb1+(x)); \
	sum1L = MADD64(sum1L, vLo,  c1); \
}

#define MC2M(x)	{ \
		c1 = *coef;		coef++;		c2 = *coef;		coef++; \
		vLo = *(vb1+(x));	vHi = *(vb1+(23-(x))); \
		sum1L = MADD64(sum1L, vLo,  c1);	sum2L = MADD64(sum2L, vLo,  c2); \
		sum1L = MADD64(sum1L, vHi, -c2);	sum2L = MADD64(sum2L, vHi,  c1); \
}

/**************************************************************************************
 * Function:    PolyphaseMono
 *
 * Description: filter one subband and produce 32 output PCM samples for one channel
 *
 * Inputs:      pointer to PCM output buffer
 *              number of "extra shifts" (vbuf format = Q(DQ_FRACBITS_OUT-2))
 *              pointer to start of vbuf (preserved from last call)
 *              start of filter coefficient table (in proper, shuffled order)
 *              no minimum number of guard bits is required for input vbuf
 *                (see additional scaling comments below)
 *
 * Outputs:     32 samples of one channel of decoded PCM data, (i.e. Q16.0)
 *
 * Return:      none
 *
 * TODO:        add 32-bit version for platforms where 64-bit mul-acc is not supported
 *                (note max filter gain - see polyCoef[] comments)
 **************************************************************************************/