bitstream.c
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上传日期:2007-06-06
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- /* ***** 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 (jrecker@real.com), Ken Cooke (kenc@real.com)
- * June 2003
- *
- * bitstream.c - bitstream unpacking, frame header parsing, side info parsing
- **************************************************************************************/
- #include "coder.h"
- #include "assembly.h"
- /**************************************************************************************
- * Function: SetBitstreamPointer
- *
- * Description: initialize bitstream reader
- *
- * Inputs: pointer to BitStreamInfo struct
- * number of bytes in bitstream
- * pointer to byte-aligned buffer of data to read from
- *
- * Outputs: filled bitstream info struct
- *
- * Return: none
- **************************************************************************************/
- void SetBitstreamPointer(BitStreamInfo *bsi, int nBytes, unsigned char *buf)
- {
- /* init bitstream */
- bsi->bytePtr = buf;
- bsi->iCache = 0; /* 4-byte unsigned int */
- bsi->cachedBits = 0; /* i.e. zero bits in cache */
- bsi->nBytes = nBytes;
- }
- /**************************************************************************************
- * Function: RefillBitstreamCache
- *
- * Description: read new data from bitstream buffer into bsi cache
- *
- * Inputs: pointer to initialized BitStreamInfo struct
- *
- * Outputs: updated bitstream info struct
- *
- * Return: none
- *
- * Notes: only call when iCache is completely drained (resets bitOffset to 0)
- * always loads 4 new bytes except when bsi->nBytes < 4 (end of buffer)
- * stores data as big-endian in cache, regardless of machine endian-ness
- *
- * TODO: optimize for ARM
- * possibly add little/big-endian modes for doing 32-bit loads
- **************************************************************************************/
- static __inline void RefillBitstreamCache(BitStreamInfo *bsi)
- {
- int nBytes = bsi->nBytes;
- /* optimize for common case, independent of machine endian-ness */
- if (nBytes >= 4) {
- bsi->iCache = (*bsi->bytePtr++) << 24;
- bsi->iCache |= (*bsi->bytePtr++) << 16;
- bsi->iCache |= (*bsi->bytePtr++) << 8;
- bsi->iCache |= (*bsi->bytePtr++);
- bsi->cachedBits = 32;
- bsi->nBytes -= 4;
- } else {
- bsi->iCache = 0;
- while (nBytes--) {
- bsi->iCache |= (*bsi->bytePtr++);
- bsi->iCache <<= 8;
- }
- bsi->iCache <<= ((3 - bsi->nBytes)*8);
- bsi->cachedBits = 8*bsi->nBytes;
- bsi->nBytes = 0;
- }
- }
- /**************************************************************************************
- * Function: GetBits
- *
- * Description: get bits from bitstream, advance bitstream pointer
- *
- * Inputs: pointer to initialized BitStreamInfo struct
- * number of bits to get from bitstream
- *
- * Outputs: updated bitstream info struct
- *
- * Return: the next nBits bits of data from bitstream buffer
- *
- * Notes: nBits must be in range [0, 31], nBits outside this range masked by 0x1f
- * for speed, does not indicate error if you overrun bit buffer
- * if nBits = 0, returns 0 (useful for scalefactor unpacking)
- *
- * TODO: optimize for ARM
- **************************************************************************************/
- unsigned int GetBits(BitStreamInfo *bsi, int nBits)
- {
- unsigned int data, lowBits;
- nBits &= 0x1f; /* nBits mod 32 to avoid unpredictable results like >> by negative amount */
- data = bsi->iCache >> (31 - nBits); /* unsigned >> so zero-extend */
- data >>= 1; /* do as >> 31, >> 1 so that nBits = 0 works okay (returns 0) */
- bsi->iCache <<= nBits; /* left-justify cache */
- bsi->cachedBits -= nBits; /* how many bits have we drawn from the cache so far */
- /* if we cross an int boundary, refill the cache */
- if (bsi->cachedBits < 0) {
- lowBits = -bsi->cachedBits;
- RefillBitstreamCache(bsi);
- data |= bsi->iCache >> (32 - lowBits); /* get the low-order bits */
-
- bsi->cachedBits -= lowBits; /* how many bits have we drawn from the cache so far */
- bsi->iCache <<= lowBits; /* left-justify cache */
- }
- return data;
- }
- /**************************************************************************************
- * Function: CalcBitsUsed
- *
- * Description: calculate how many bits have been read from bitstream
- *
- * Inputs: pointer to initialized BitStreamInfo struct
- * pointer to start of bitstream buffer
- * bit offset into first byte of startBuf (0-7)
- *
- * Outputs: none
- *
- * Return: number of bits read from bitstream, as offset from startBuf:startOffset
- **************************************************************************************/
- int CalcBitsUsed(BitStreamInfo *bsi, unsigned char *startBuf, int startOffset)
- {
- int bitsUsed;
- bitsUsed = (bsi->bytePtr - startBuf) * 8;
- bitsUsed -= bsi->cachedBits;
- bitsUsed -= startOffset;
- return bitsUsed;
- }
- /**************************************************************************************
- * Function: CheckPadBit
- *
- * Description: check whether padding byte is present in an MP3 frame
- *
- * Inputs: MP3DecInfo struct with valid FrameHeader struct
- * (filled by UnpackFrameHeader())
- *
- * Outputs: none
- *
- * Return: 1 if pad bit is set, 0 if not, -1 if null input pointer
- **************************************************************************************/
- int CheckPadBit(MP3DecInfo *mp3DecInfo)
- {
- FrameHeader *fh;
- /* validate pointers */
- if (!mp3DecInfo || !mp3DecInfo->FrameHeaderPS)
- return -1;
- fh = ((FrameHeader *)(mp3DecInfo->FrameHeaderPS));
- return (fh->paddingBit ? 1 : 0);
- }
- /**************************************************************************************
- * Function: UnpackFrameHeader
- *
- * Description: parse the fields of the MP3 frame header
- *
- * Inputs: buffer pointing to a complete MP3 frame header (4 bytes, plus 2 if CRC)
- *
- * Outputs: filled frame header info in the MP3DecInfo structure
- * updated platform-specific FrameHeader struct
- *
- * Return: length (in bytes) of frame header (for caller to calculate offset to
- * first byte following frame header)
- * -1 if null frameHeader or invalid header
- *
- * TODO: check for valid modes, depending on capabilities of decoder
- * test CRC on actual stream (verify no endian problems)
- **************************************************************************************/
- int UnpackFrameHeader(MP3DecInfo *mp3DecInfo, unsigned char *buf)
- {
- int verIdx;
- FrameHeader *fh;
- /* validate pointers and sync word */
- if (!mp3DecInfo || !mp3DecInfo->FrameHeaderPS || (buf[0] & SYNCWORDH) != SYNCWORDH || (buf[1] & SYNCWORDL) != SYNCWORDL)
- return -1;
- fh = ((FrameHeader *)(mp3DecInfo->FrameHeaderPS));
- /* read header fields - use bitmasks instead of GetBits() for speed, since format never varies */
- verIdx = (buf[1] >> 3) & 0x03;
- fh->ver = (MPEGVersion)( verIdx == 0 ? MPEG25 : ((verIdx & 0x01) ? MPEG1 : MPEG2) );
- fh->layer = 4 - ((buf[1] >> 1) & 0x03); /* easy mapping of index to layer number, 4 = error */
- fh->crc = 1 - ((buf[1] >> 0) & 0x01);
- fh->brIdx = (buf[2] >> 4) & 0x0f;
- fh->srIdx = (buf[2] >> 2) & 0x03;
- fh->paddingBit = (buf[2] >> 1) & 0x01;
- fh->privateBit = (buf[2] >> 0) & 0x01;
- fh->sMode = (StereoMode)((buf[3] >> 6) & 0x03); /* maps to correct enum (see definition) */
- fh->modeExt = (buf[3] >> 4) & 0x03;
- fh->copyFlag = (buf[3] >> 3) & 0x01;
- fh->origFlag = (buf[3] >> 2) & 0x01;
- fh->emphasis = (buf[3] >> 0) & 0x03;
- /* check parameters to avoid indexing tables with bad values */
- if (fh->srIdx == 3 || fh->layer == 4 || fh->brIdx == 15)
- return -1;
- fh->sfBand = &sfBandTable[fh->ver][fh->srIdx]; /* for readability (we reference sfBandTable many times in decoder) */
- if (fh->sMode != Joint) /* just to be safe (dequant, stproc check fh->modeExt) */
- fh->modeExt = 0;
- /* init user-accessible data */
- mp3DecInfo->nChans = (fh->sMode == Mono ? 1 : 2);
- mp3DecInfo->samprate = samplerateTab[fh->ver][fh->srIdx];
- mp3DecInfo->nGrans = (fh->ver == MPEG1 ? NGRANS_MPEG1 : NGRANS_MPEG2);
- mp3DecInfo->nGranSamps = ((int)samplesPerFrameTab[fh->ver][fh->layer - 1]) / mp3DecInfo->nGrans;
- mp3DecInfo->layer = fh->layer;
- mp3DecInfo->version = fh->ver;
-
- /* get bitrate and nSlots from table, unless brIdx == 0 (free mode) in which case caller must figure it out himself
- * question - do we want to overwrite mp3DecInfo->bitrate with 0 each time if it's free mode, and
- * copy the pre-calculated actual free bitrate into it in mp3dec.c (according to the spec,
- * this shouldn't be necessary, since it should be either all frames free or none free)
- */
- if (fh->brIdx) {
- mp3DecInfo->bitrate = ((int)bitrateTab[fh->ver][fh->layer - 1][fh->brIdx]) * 1000;
-
- /* nSlots = total frame bytes (from table) - sideInfo bytes - header - CRC (if present) + pad (if present) */
- mp3DecInfo->nSlots = (int)slotTab[fh->ver][fh->srIdx][fh->brIdx] -
- (int)sideBytesTab[fh->ver][(fh->sMode == Mono ? 0 : 1)] -
- 4 - (fh->crc ? 2 : 0) + (fh->paddingBit ? 1 : 0);
- }
- /* load crc word, if enabled, and return length of frame header (in bytes) */
- if (fh->crc) {
- fh->CRCWord = ((int)buf[4] << 8 | (int)buf[5] << 0);
- return 6;
- } else {
- fh->CRCWord = 0;
- return 4;
- }
- }
- /**************************************************************************************
- * Function: UnpackSideInfo
- *
- * Description: parse the fields of the MP3 side info header
- *
- * Inputs: MP3DecInfo structure filled by UnpackFrameHeader()
- * buffer pointing to the MP3 side info data
- *
- * Outputs: updated mainDataBegin in MP3DecInfo struct
- * updated private (platform-specific) SideInfo struct
- *
- * Return: length (in bytes) of side info data
- * -1 if null input pointers
- **************************************************************************************/
- int UnpackSideInfo(MP3DecInfo *mp3DecInfo, unsigned char *buf)
- {
- int gr, ch, bd, nBytes;
- BitStreamInfo bitStreamInfo, *bsi;
- FrameHeader *fh;
- SideInfo *si;
- SideInfoSub *sis;
- /* validate pointers and sync word */
- if (!mp3DecInfo || !mp3DecInfo->FrameHeaderPS || !mp3DecInfo->SideInfoPS)
- return -1;
- fh = ((FrameHeader *)(mp3DecInfo->FrameHeaderPS));
- si = ((SideInfo *)(mp3DecInfo->SideInfoPS));
- bsi = &bitStreamInfo;
- if (fh->ver == MPEG1) {
- /* MPEG 1 */
- nBytes = (fh->sMode == Mono ? SIBYTES_MPEG1_MONO : SIBYTES_MPEG1_STEREO);
- SetBitstreamPointer(bsi, nBytes, buf);
- si->mainDataBegin = GetBits(bsi, 9);
- si->privateBits = GetBits(bsi, (fh->sMode == Mono ? 5 : 3));
- for (ch = 0; ch < mp3DecInfo->nChans; ch++)
- for (bd = 0; bd < MAX_SCFBD; bd++)
- si->scfsi[ch][bd] = GetBits(bsi, 1);
- } else {
- /* MPEG 2, MPEG 2.5 */
- nBytes = (fh->sMode == Mono ? SIBYTES_MPEG2_MONO : SIBYTES_MPEG2_STEREO);
- SetBitstreamPointer(bsi, nBytes, buf);
- si->mainDataBegin = GetBits(bsi, 8);
- si->privateBits = GetBits(bsi, (fh->sMode == Mono ? 1 : 2));
- }
- for(gr =0; gr < mp3DecInfo->nGrans; gr++) {
- for (ch = 0; ch < mp3DecInfo->nChans; ch++) {
- sis = &si->sis[gr][ch]; /* side info subblock for this granule, channel */
- sis->part23Length = GetBits(bsi, 12);
- sis->nBigvals = GetBits(bsi, 9);
- sis->globalGain = GetBits(bsi, 8);
- sis->sfCompress = GetBits(bsi, (fh->ver == MPEG1 ? 4 : 9));
- sis->winSwitchFlag = GetBits(bsi, 1);
- if(sis->winSwitchFlag) {
- /* this is a start, stop, short, or mixed block */
- sis->blockType = GetBits(bsi, 2); /* 0 = normal, 1 = start, 2 = short, 3 = stop */
- sis->mixedBlock = GetBits(bsi, 1); /* 0 = not mixed, 1 = mixed */
- sis->tableSelect[0] = GetBits(bsi, 5);
- sis->tableSelect[1] = GetBits(bsi, 5);
- sis->tableSelect[2] = 0; /* unused */
- sis->subBlockGain[0] = GetBits(bsi, 3);
- sis->subBlockGain[1] = GetBits(bsi, 3);
- sis->subBlockGain[2] = GetBits(bsi, 3);
- /* TODO - check logic */
- if (sis->blockType == 0) {
- /* this should not be allowed, according to spec */
- sis->nBigvals = 0;
- sis->part23Length = 0;
- sis->sfCompress = 0;
- } else if (sis->blockType == 2 && sis->mixedBlock == 0) {
- /* short block, not mixed */
- sis->region0Count = 8;
- } else {
- /* start, stop, or short-mixed */
- sis->region0Count = 7;
- }
- sis->region1Count = 20 - sis->region0Count;
- } else {
- /* this is a normal block */
- sis->blockType = 0;
- sis->mixedBlock = 0;
- sis->tableSelect[0] = GetBits(bsi, 5);
- sis->tableSelect[1] = GetBits(bsi, 5);
- sis->tableSelect[2] = GetBits(bsi, 5);
- sis->region0Count = GetBits(bsi, 4);
- sis->region1Count = GetBits(bsi, 3);
- }
- sis->preFlag = (fh->ver == MPEG1 ? GetBits(bsi, 1) : 0);
- sis->sfactScale = GetBits(bsi, 1);
- sis->count1TableSelect = GetBits(bsi, 1);
- }
- }
- mp3DecInfo->mainDataBegin = si->mainDataBegin; /* needed by main decode loop */
- ASSERT(nBytes == CalcBitsUsed(bsi, buf, 0) >> 3);
- return nBytes;
- }