huffman.c

著名的 helix realplayer 基于手机 symbian 系统的 播放器全套源代码

						return -1;
					while (cachedBits < minBits) {
						cache |= (unsigned int)(*buf++) << (24 - cachedBits);
						cachedBits += 8;
						bitsLeft -= 8;
					}
					if (bitsLeft < 0) {
						cachedBits += bitsLeft;
						bitsLeft = 0;
						cache &= (signed int)0x80000000 >> (cachedBits - 1);
					}
					y += (int)(cache >> (32 - linBits));
					cachedBits -= linBits;
					cache <<= linBits;
				}
				if (y)	{ApplySign(y, cache); cache <<= 1; cachedBits--;}

				/* ran out of bits - should never have consumed padBits */
				if (cachedBits < padBits)
					return -1;

				*xy++ = x;
				*xy++ = y;
				nVals -= 2;
				tCurr = tBase;
			}
		}
		bitsLeft += (cachedBits - padBits);
		return (startBits - bitsLeft);
	}

	/* error in bitstream - trying to access unused Huffman table */
	return -1;
}

/**************************************************************************************
 * Function:    DecodeHuffmanQuads
 *
 * Description: decode 4-way vector Huffman codes in the "count1" region of spectrum
 *
 * Inputs:      valid BitStreamInfo struct, pointing to start of quadword codes
 *              pointer to vwxy buffer to received decoded values
 *              maximum number of codewords to decode
 *              index of quadword table (0 = table A, 1 = table B)
 *              number of bits remaining in bitstream
 *
 * Outputs:     quadruples of decoded coefficients in vwxy
 *              updated BitStreamInfo struct
 *
 * Return:      index of the first "zero_part" value (index of the first sample 
 *                of the quad word after which all samples are 0)
 * 
 * Notes:        si_huff.bit tests every vwxy output in both quad tables
 **************************************************************************************/
static int DecodeHuffmanQuads(int *vwxy, int nVals, int tabIdx, int bitsLeft, unsigned char *buf, int bitOffset)
{
	int i, v, w, x, y;
	int len, maxBits, cachedBits, padBits;
	unsigned int cache;
	unsigned char cw, *tBase;

	if (bitsLeft <= 0)
		return 0;

	tBase = (unsigned char *)quadTable + quadTabOffset[tabIdx];
	maxBits = quadTabMaxBits[tabIdx];

	/* initially fill cache with any partial byte */
	cache = 0;
	cachedBits = (8 - bitOffset) & 0x07;
	if (cachedBits)
		cache = (unsigned int)(*buf++) << (32 - cachedBits);
	bitsLeft -= cachedBits;

	i = padBits = 0;
	while (i < (nVals - 3)) {
		/* refill cache - assumes cachedBits <= 16 */
		if (bitsLeft >= 16) {
			/* load 2 new bytes into left-justified cache */
			cache |= (unsigned int)(*buf++) << (24 - cachedBits);
			cache |= (unsigned int)(*buf++) << (16 - cachedBits);
			cachedBits += 16;
			bitsLeft -= 16;
		} else {
			/* last time through, pad cache with zeros and drain cache */
			if (cachedBits + bitsLeft <= 0) return i;
			if (bitsLeft > 0)	cache |= (unsigned int)(*buf++) << (24 - cachedBits);
			if (bitsLeft > 8)	cache |= (unsigned int)(*buf++) << (16 - cachedBits);
			cachedBits += bitsLeft;
			bitsLeft = 0;

			cache &= (signed int)0x80000000 >> (cachedBits - 1);
			padBits = 10;
			cachedBits += padBits;	/* okay if this is > 32 (0's automatically shifted in from right) */
		}

		/* largest maxBits = 6, plus 4 for sign bits, so make sure cache has at least 10 bits */
		while (i < (nVals - 3) && cachedBits >= 10 ) {
			cw = tBase[cache >> (32 - maxBits)];
			len = GetHLenQ(cw);
			cachedBits -= len;
			cache <<= len;

			v = GetCWVQ(cw);	if(v) {ApplySign(v, cache); cache <<= 1; cachedBits--;}
			w = GetCWWQ(cw);	if(w) {ApplySign(w, cache); cache <<= 1; cachedBits--;}
			x = GetCWXQ(cw);	if(x) {ApplySign(x, cache); cache <<= 1; cachedBits--;}
			y = GetCWYQ(cw);	if(y) {ApplySign(y, cache); cache <<= 1; cachedBits--;}

			/* ran out of bits - okay (means we're done) */
			if (cachedBits < padBits)
				return i;

			*vwxy++ = v;
			*vwxy++ = w;
			*vwxy++ = x;
			*vwxy++ = y;
			i += 4;
		}
	}

	/* decoded max number of quad values */
	return i;
}

/**************************************************************************************
 * Function:    DecodeHuffman
 *
 * Description: decode one granule, one channel worth of Huffman codes
 *
 * Inputs:      MP3DecInfo structure filled by UnpackFrameHeader(), UnpackSideInfo(),
 *                and UnpackScaleFactors() (for this granule)
 *              buffer pointing to start of Huffman data in MP3 frame
 *              pointer to bit offset (0-7) indicating starting bit in buf[0]
 *              number of bits in the Huffman data section of the frame
 *                (could include padding bits)
 *              index of current granule and channel
 *
 * Outputs:     decoded coefficients in hi->huffDecBuf[ch] (hi pointer in mp3DecInfo)
 *              updated bitOffset
 *
 * Return:      length (in bytes) of Huffman codes
 *              bitOffset also returned in parameter (0 = MSB, 7 = LSB of 
 *                byte located at buf + offset)
 *              -1 if null input pointers, huffBlockBits < 0, or decoder runs 
 *                out of bits prematurely (invalid bitstream)
 **************************************************************************************/
int DecodeHuffman(MP3DecInfo *mp3DecInfo, unsigned char *buf, int *bitOffset, int huffBlockBits, int gr, int ch)
{
	int r1Start, r2Start, rEnd[4];	/* region boundaries */
	int i, w, bitsUsed, bitsLeft;
	unsigned char *startBuf = buf;

	FrameHeader *fh;
	SideInfo *si;
	SideInfoSub *sis;
	ScaleFactorInfo *sfi;
	HuffmanInfo *hi;

	/* validate pointers */
	if (!mp3DecInfo || !mp3DecInfo->FrameHeaderPS || !mp3DecInfo->SideInfoPS || !mp3DecInfo->ScaleFactorInfoPS || !mp3DecInfo->HuffmanInfoPS)
		return -1;

	fh = ((FrameHeader *)(mp3DecInfo->FrameHeaderPS));
	si = ((SideInfo *)(mp3DecInfo->SideInfoPS));
	sis = &si->sis[gr][ch];
	sfi = ((ScaleFactorInfo *)(mp3DecInfo->ScaleFactorInfoPS));
	hi = (HuffmanInfo*)(mp3DecInfo->HuffmanInfoPS);

	if (huffBlockBits < 0)
		return -1;

	/* figure out region boundaries (the first 2*bigVals coefficients divided into 3 regions) */
	if (sis->winSwitchFlag && sis->blockType == 2) {
		if (sis->mixedBlock == 0) {
			r1Start = fh->sfBand->s[(sis->region0Count + 1)/3] * 3;
		} else {
			if (fh->ver == MPEG1) {
				r1Start = fh->sfBand->l[sis->region0Count + 1];
			} else {
				/* see MPEG2 spec for explanation */
				w = fh->sfBand->s[4] - fh->sfBand->s[3];
				r1Start = fh->sfBand->l[6] + 2*w;
			}
		}
		r2Start = MAX_NSAMP;	/* short blocks don't have region 2 */
	} else {
		r1Start = fh->sfBand->l[sis->region0Count + 1];
		r2Start = fh->sfBand->l[sis->region0Count + 1 + sis->region1Count + 1];
	}

	/* offset rEnd index by 1 so first region = rEnd[1] - rEnd[0], etc. */
	rEnd[3] = MIN(MAX_NSAMP, 2 * sis->nBigvals);
	rEnd[2] = MIN(r2Start, rEnd[3]);
	rEnd[1] = MIN(r1Start, rEnd[3]);
	rEnd[0] = 0;

	/* rounds up to first all-zero pair (we don't check last pair for (x,y) == (non-zero, zero)) */
	hi->nonZeroBound[ch] = rEnd[3];

	/* decode Huffman pairs (rEnd[i] are always even numbers) */
	bitsLeft = huffBlockBits;
	for (i = 0; i < 3; i++) {
		bitsUsed = DecodeHuffmanPairs(hi->huffDecBuf[ch] + rEnd[i], rEnd[i+1] - rEnd[i], sis->tableSelect[i], bitsLeft, buf, *bitOffset);
		if (bitsUsed < 0 || bitsUsed > bitsLeft)	/* error - overran end of bitstream */
			return -1;

		/* update bitstream position */
		buf += (bitsUsed + *bitOffset) >> 3;
		*bitOffset = (bitsUsed + *bitOffset) & 0x07;
		bitsLeft -= bitsUsed;
	}

	/* decode Huffman quads (if any) */
	hi->nonZeroBound[ch] += DecodeHuffmanQuads(hi->huffDecBuf[ch] + rEnd[3], MAX_NSAMP - rEnd[3], sis->count1TableSelect, bitsLeft, buf, *bitOffset);

	ASSERT(hi->nonZeroBound[ch] <= MAX_NSAMP);
	for (i = hi->nonZeroBound[ch]; i < MAX_NSAMP; i++)
		hi->huffDecBuf[ch][i] = 0;
	
	/* If bits used for 576 samples < huffBlockBits, then the extras are considered
	 *  to be stuffing bits (throw away, but need to return correct bitstream position) 
	 */
	buf += (bitsLeft + *bitOffset) >> 3;
	*bitOffset = (bitsLeft + *bitOffset) & 0x07;
	
	return (buf - startBuf);
}