sbrhuff.c

nds上大名鼎鼎的DSOrganize 2.8最新源代码。很值得研究。

/* ***** BEGIN LICENSE BLOCK *****  
 * Source last modified: $Id: sbrhuff.c,v 1.1.2.1 2005/02/26 02:05:12 jrecker Exp $ 
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/**************************************************************************************
 * Fixed-point HE-AAC decoder
 * Jon Recker ([e-mail])
 * February 2005
 *
 * sbrhuff.c - functions for unpacking Huffman-coded envelope and noise data
 **************************************************************************************/

#include "sbr.h"
#include "assembly.h"

/**************************************************************************************
 * Function:    DecodeHuffmanScalar
 *
 * Description: decode one Huffman symbol from bitstream
 *
 * Inputs:      pointers to Huffman table and info struct
 *              left-aligned bit buffer with >= huffTabInfo->maxBits bits
 *
 * Outputs:     decoded symbol in *val
 *
 * Return:      number of bits in symbol
 *
 * Notes:       assumes canonical Huffman codes:
 *                first CW always 0, we have "count" CW's of length "nBits" bits
 *                starting CW for codes of length nBits+1 = 
 *                  (startCW[nBits] + count[nBits]) << 1
 *                if there are no codes at nBits, then we just keep << 1 each time 
 *                  (since count[nBits] = 0)
 **************************************************************************************/
static int DecodeHuffmanScalar(const signed short *huffTab, const HuffInfo *huffTabInfo, unsigned int bitBuf, signed int *val)
{
    unsigned int count, start, shift, t;
	const unsigned char *countPtr;
	const signed short *map;

	map = huffTab + huffTabInfo->offset;
	countPtr = huffTabInfo->count;

	start = 0;
	count = 0;
	shift = 32;
	do {
		start += count;
		start <<= 1;
		map += count;
		count = *countPtr++;
		shift--;
		t = (bitBuf >> shift) - start;
	} while (t >= count);
	
	*val = (signed int)map[t];
	return (countPtr - huffTabInfo->count);
}

/**************************************************************************************
 * Function:    DecodeOneSymbol
 *
 * Description: dequantize one Huffman symbol from bitstream, 
 *                using table huffTabSBR[huffTabIndex]
 *
 * Inputs:      BitStreamInfo struct pointing to start of next Huffman codeword
 *              index of Huffman table
 *
 * Outputs:     bitstream advanced by number of bits in codeword
 *
 * Return:      one decoded symbol
 **************************************************************************************/
static int DecodeOneSymbol(BitStreamInfo *bsi, int huffTabIndex)
{
	int nBits, val;
	unsigned int bitBuf;
	const HuffInfo *hi;

	hi = &(huffTabSBRInfo[huffTabIndex]);

	bitBuf = GetBitsNoAdvance(bsi, hi->maxBits) << (32 - hi->maxBits);
	nBits = DecodeHuffmanScalar(huffTabSBR, hi, bitBuf, &val);
	AdvanceBitstream(bsi, nBits);
	
	return val;
}

/* [1.0, sqrt(2)], format = Q29 (one guard bit for decoupling) */
static const int envDQTab[2] = {0x20000000, 0x2d413ccc};

/**************************************************************************************
 * Function:    DequantizeEnvelope
 *
 * Description: dequantize envelope scalefactors
 *
 * Inputs:      number of scalefactors to process
 *              amplitude resolution flag for this frame (0 or 1)
 *              quantized envelope scalefactors
 * 
 * Outputs:     dequantized envelope scalefactors
 *
 * Return:      extra int bits in output (6 + expMax)
 *              in other words, output format = Q(FBITS_OUT_DQ_ENV - (6 + expMax))
 *
 * Notes:       dequantized scalefactors have at least 2 GB
 **************************************************************************************/
static int DequantizeEnvelope(int nBands, int ampRes, signed char *envQuant, int *envDequant)
{
	int exp, expMax, i, scalei;

	if (nBands <= 0)
		return 0;
	
	/* scan for largest dequant value (do separately from envelope decoding to keep code cleaner) */
	expMax = 0;
	for (i = 0; i < nBands; i++) {
		if (envQuant[i] > expMax)
			expMax = envQuant[i];
	}

	/* dequantized envelope gains
	 *   envDequant = 64*2^(envQuant / alpha) = 2^(6 + envQuant / alpha)
	 *     if ampRes == 0, alpha = 2 and range of envQuant = [0, 127]
	 *     if ampRes == 1, alpha = 1 and range of envQuant = [0, 63]
	 * also if coupling is on, envDequant is scaled by something in range [0, 2]
	 * so range of envDequant = [2^6, 2^69] (no coupling), [2^6, 2^70] (with coupling)
	 * 
	 * typical range (from observation) of envQuant/alpha = [0, 27] --> largest envQuant ~= 2^33
	 * output: Q(29 - (6 + expMax))
	 *
	 * reference: 14496-3:2001(E)/4.6.18.3.5 and 14496-4:200X/FPDAM8/5.6.5.1.2.1.5
	 */
	if (ampRes) {
		do {
			exp = *envQuant++;
			scalei = MIN(expMax - exp, 31);
			*envDequant++ = envDQTab[0] >> scalei;
		} while (--nBands);

		return (6 + expMax);
	} else {
		expMax >>= 1;
		do {
			exp = *envQuant++;
			scalei = MIN(expMax - (exp >> 1), 31);
			*envDequant++ = envDQTab[exp & 0x01] >> scalei;
		} while (--nBands);

		return (6 + expMax);
	}

}

/**************************************************************************************
 * Function:    DequantizeNoise
 *
 * Description: dequantize noise scalefactors
 *
 * Inputs:      number of scalefactors to process
 *              quantized noise scalefactors
 * 
 * Outputs:     dequantized noise scalefactors, format = Q(FBITS_OUT_DQ_NOISE)
 *
 * Return:      none
 *
 * Notes:       dequantized scalefactors have at least 2 GB
 **************************************************************************************/
static void DequantizeNoise(int nBands, signed char *noiseQuant, int *noiseDequant)
{
	int exp, scalei;
	
	if (nBands <= 0)
		return;

	/* dequantize noise floor gains (4.6.18.3.5):
	 *   noiseDequant = 2^(NOISE_FLOOR_OFFSET - noiseQuant)
	 *
	 * range of noiseQuant = [0, 30] (see 4.6.18.3.6), NOISE_FLOOR_OFFSET = 6
	 *   so range of noiseDequant = [2^-24, 2^6]
	 */
	do {
		exp = *noiseQuant++;
		scalei = NOISE_FLOOR_OFFSET - exp + FBITS_OUT_DQ_NOISE;	/* 6 + 24 - exp, exp = [0,30] */

		if (scalei < 0)
			*noiseDequant++ = 0;
		else if (scalei < 30)
			*noiseDequant++ = 1 << scalei;
		else
			*noiseDequant++ = 0x3fffffff;	/* leave 2 GB */

	} while (--nBands);
}

/**************************************************************************************
 * Function:    DecodeSBREnvelope
 *
 * Description: decode delta Huffman coded envelope scalefactors from bitstream
 *
 * Inputs:      BitStreamInfo struct pointing to start of env data
 *              initialized PSInfoSBR struct
 *              initialized SBRGrid struct for this channel
 *              initialized SBRFreq struct for this SCE/CPE block
 *              initialized SBRChan struct for this channel
 *              index of current channel (0 for SCE, 0 or 1 for CPE)
 *