path: root/circuitpython/lib/mp3/src/scalfact.c

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 * Version: RCSL 1.0/RPSL 1.0 
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 * ***** END LICENSE BLOCK ***** */ 

/**************************************************************************************
 * Fixed-point MP3 decoder
 * Jon Recker (jrecker@real.com), Ken Cooke (kenc@real.com)
 * June 2003
 *
 * scalfact.c - scalefactor unpacking functions
 **************************************************************************************/

#include "coder.h"

/* scale factor lengths (num bits) */
static const char SFLenTab[16][2] = {
	{0, 0},    {0, 1},
	{0, 2},    {0, 3},
	{3, 0},    {1, 1},
	{1, 2},    {1, 3},
	{2, 1},    {2, 2},
	{2, 3},    {3, 1},
	{3, 2},    {3, 3},
	{4, 2},    {4, 3},
};

/**************************************************************************************
 * Function:    UnpackSFMPEG1
 *
 * Description: unpack MPEG 1 scalefactors from bitstream
 *
 * Inputs:      BitStreamInfo, SideInfoSub, ScaleFactorInfoSub structs for this
 *                granule/channel
 *              vector of scfsi flags from side info, length = 4 (MAX_SCFBD)
 *              index of current granule
 *              ScaleFactorInfoSub from granule 0 (for granule 1, if scfsi[i] is set, 
 *                then we just replicate the scale factors from granule 0 in the
 *                i'th set of scalefactor bands)
 *
 * Outputs:     updated BitStreamInfo struct
 *              scalefactors in sfis (short and/or long arrays, as appropriate)
 *
 * Return:      none
 *
 * Notes:       set order of short blocks to s[band][window] instead of s[window][band]
 *                so that we index through consectutive memory locations when unpacking 
 *                (make sure dequantizer follows same convention)
 *              Illegal Intensity Position = 7 (always) for MPEG1 scale factors
 **************************************************************************************/
static void UnpackSFMPEG1(BitStreamInfo *bsi, SideInfoSub *sis, ScaleFactorInfoSub *sfis, int *scfsi, int gr, ScaleFactorInfoSub *sfisGr0)
{
	int sfb;
	int slen0, slen1;
	
	/* these can be 0, so make sure GetBits(bsi, 0) returns 0 (no >> 32 or anything) */
	slen0 = (int)SFLenTab[sis->sfCompress][0];
	slen1 = (int)SFLenTab[sis->sfCompress][1];
	
	if (sis->blockType == 2) {
		/* short block, type 2 (implies winSwitchFlag == 1) */
		if (sis->mixedBlock) {          
			/* do long block portion */
			for (sfb = 0; sfb < 8; sfb++)
				sfis->l[sfb] =    (char)GetBits(bsi, slen0);
			sfb = 3;
		} else {
			/* all short blocks */
			sfb = 0;
		}

		for (      ; sfb < 6; sfb++) {
			sfis->s[sfb][0] = (char)GetBits(bsi, slen0);
			sfis->s[sfb][1] = (char)GetBits(bsi, slen0);
			sfis->s[sfb][2] = (char)GetBits(bsi, slen0);
		}

		for (      ; sfb < 12; sfb++) {
			sfis->s[sfb][0] = (char)GetBits(bsi, slen1);
			sfis->s[sfb][1] = (char)GetBits(bsi, slen1);
			sfis->s[sfb][2] = (char)GetBits(bsi, slen1);
		}

		/* last sf band not transmitted */
		sfis->s[12][0] = sfis->s[12][1] = sfis->s[12][2] = 0;
	} else {
		/* long blocks, type 0, 1, or 3 */
		if(gr == 0) {
			/* first granule */
			for (sfb = 0;  sfb < 11; sfb++) 
				sfis->l[sfb] = (char)GetBits(bsi, slen0);
			for (sfb = 11; sfb < 21; sfb++) 
				sfis->l[sfb] = (char)GetBits(bsi, slen1);
			return;
		} else {
			/* second granule
			 * scfsi: 0 = different scalefactors for each granule, 1 = copy sf's from granule 0 into granule 1 
			 * for block type == 2, scfsi is always 0
			 */
			sfb = 0;
			if(scfsi[0])  for(  ; sfb < 6 ; sfb++) sfis->l[sfb] = sfisGr0->l[sfb];
			else          for(  ; sfb < 6 ; sfb++) sfis->l[sfb] = (char)GetBits(bsi, slen0);
			if(scfsi[1])  for(  ; sfb <11 ; sfb++) sfis->l[sfb] = sfisGr0->l[sfb];
			else          for(  ; sfb <11 ; sfb++) sfis->l[sfb] = (char)GetBits(bsi, slen0);
			if(scfsi[2])  for(  ; sfb <16 ; sfb++) sfis->l[sfb] = sfisGr0->l[sfb];
			else          for(  ; sfb <16 ; sfb++) sfis->l[sfb] = (char)GetBits(bsi, slen1);
			if(scfsi[3])  for(  ; sfb <21 ; sfb++) sfis->l[sfb] = sfisGr0->l[sfb];
			else          for(  ; sfb <21 ; sfb++) sfis->l[sfb] = (char)GetBits(bsi, slen1);
		}
		/* last sf band not transmitted */
		sfis->l[21] = 0;
		sfis->l[22] = 0;
	}
}

/* NRTab[size + 3*is_right][block type][partition]
 *   block type index: 0 = (bt0,bt1,bt3), 1 = bt2 non-mixed, 2 = bt2 mixed
 *   partition: scale factor groups (sfb1 through sfb4)
 * for block type = 2 (mixed or non-mixed) / by 3 is rolled into this table
 *   (for 3 short blocks per long block)
 * see 2.4.3.2 in MPEG 2 (low sample rate) spec
 * stuff rolled into this table:
 *   NRTab[x][1][y]   --> (NRTab[x][1][y])   / 3
 *   NRTab[x][2][>=1] --> (NRTab[x][2][>=1]) / 3  (first partition is long block)
 */
static const char NRTab[6][3][4] = {
	/* non-intensity stereo */
	{	{6, 5, 5, 5},		
		{3, 3, 3, 3},	/* includes / 3 */	
		{6, 3, 3, 3},   /* includes / 3 except for first entry */
	},
	{	{6, 5, 7, 3}, 
		{3, 3, 4, 2},
		{6, 3, 4, 2},
	},
	{	{11, 10, 0, 0},
		{6, 6, 0, 0},
		{6, 3, 6, 0},  /* spec = [15,18,0,0], but 15 = 6L + 9S, so move 9/3=3 into col 1, 18/3=6 into col 2 and adj. slen[1,2] below */
	},
	/* intensity stereo, right chan */
	{	{7, 7, 7, 0},
		{4, 4, 4, 0},
		{6, 5, 4, 0},
	},
	{	{6, 6, 6, 3}, 
		{4, 3, 3, 2},
		{6, 4, 3, 2},
	},
	{	{8, 8, 5, 0},
		{5, 4, 3, 0},
		{6, 6, 3, 0},
	}
};

/**************************************************************************************
 * Function:    UnpackSFMPEG2
 *
 * Description: unpack MPEG 2 scalefactors from bitstream
 *
 * Inputs:      BitStreamInfo, SideInfoSub, ScaleFactorInfoSub structs for this
 *                granule/channel
 *              index of current granule and channel
 *              ScaleFactorInfoSub from this granule 
 *              modeExt field from frame header, to tell whether intensity stereo is on
 *              ScaleFactorJS struct for storing IIP info used in Dequant()
 *
 * Outputs:     updated BitStreamInfo struct
 *              scalefactors in sfis (short and/or long arrays, as appropriate)
 *              updated intensityScale and preFlag flags
 *
 * Return:      none
 *
 * Notes:       Illegal Intensity Position = (2^slen) - 1 for MPEG2 scale factors
 *
 * TODO:        optimize the / and % stuff (only do one divide, get modulo x 
 *                with (x / m) * m, etc.)
 **************************************************************************************/
static void UnpackSFMPEG2(BitStreamInfo *bsi, SideInfoSub *sis, ScaleFactorInfoSub *sfis, int gr, int ch, int modeExt, ScaleFactorJS *sfjs)
{

	int i, sfb, sfcIdx, btIdx, nrIdx;
	int slen[4], nr[4];
	int sfCompress, preFlag, intensityScale;
	
	sfCompress = sis->sfCompress;
	preFlag = 0;
	intensityScale = 0;

	/* stereo mode bits (1 = on): bit 1 = mid-side on/off, bit 0 = intensity on/off */
	if (! ((modeExt & 0x01) && (ch == 1)) ) {
		/* in other words: if ((modeExt & 0x01) == 0 || ch == 0) */
		if (sfCompress < 400) {
			/* max slen = floor[(399/16) / 5] = 4 */
			slen[0] = (sfCompress >> 4) / 5;
			slen[1]= (sfCompress >> 4) % 5;
			slen[2]= (sfCompress & 0x0f) >> 2;
			slen[3]= (sfCompress & 0x03);
			sfcIdx = 0;
		} else if (sfCompress < 500) {
			/* max slen = floor[(99/4) / 5] = 4 */
			sfCompress -= 400;
			slen[0] = (sfCompress >> 2) / 5;
			slen[1]= (sfCompress >> 2) % 5;
			slen[2]= (sfCompress & 0x03);
			slen[3]= 0;
			sfcIdx = 1;
		} else {
			/* max slen = floor[11/3] = 3 (sfCompress = 9 bits in MPEG2) */
			sfCompress -= 500;
			slen[0] = sfCompress / 3;
			slen[1] = sfCompress % 3;
			slen[2] = slen[3] = 0;
			if (sis->mixedBlock) {
				/* adjust for long/short mix logic (see comment above in NRTab[] definition) */
				slen[2] = slen[1];  
				slen[1] = slen[0];
			}  
			preFlag = 1;
			sfcIdx = 2;
		}
	} else {    
		/* intensity stereo ch = 1 (right) */
		intensityScale = sfCompress & 0x01;
		sfCompress >>= 1;
		if (sfCompress < 180) {
			/* max slen = floor[35/6] = 5 (from mod 36) */
			slen[0] = (sfCompress / 36);
			slen[1] = (sfCompress % 36) / 6;
			slen[2] = (sfCompress % 36) % 6;
			slen[3] = 0;
			sfcIdx = 3;
		} else if (sfCompress < 244) {
			/* max slen = floor[63/16] = 3 */
			sfCompress -= 180;
			slen[0] = (sfCompress & 0x3f) >> 4;
			slen[1] = (sfCompress & 0x0f) >> 2;
			slen[2] = (sfCompress & 0x03);
			slen[3] = 0;
			sfcIdx = 4;
		} else {
			/* max slen = floor[11/3] = 3 (max sfCompress >> 1 = 511/2 = 255) */
			sfCompress -= 244;
			slen[0] = (sfCompress / 3);
			slen[1] = (sfCompress % 3);
			slen[2] = slen[3] = 0;
			sfcIdx = 5;
		}
	}
	
	/* set index based on block type: (0,1,3) --> 0, (2 non-mixed) --> 1, (2 mixed) ---> 2 */
	btIdx = 0;
	if (sis->blockType == 2) 
		btIdx = (sis->mixedBlock ? 2 : 1);
	for (i = 0; i < 4; i++)
		nr[i] = (int)NRTab[sfcIdx][btIdx][i];

	/* save intensity stereo scale factor info */
	if( (modeExt & 0x01) && (ch == 1) ) {
		for (i = 0; i < 4; i++) {
			sfjs->slen[i] = slen[i];
			sfjs->nr[i] = nr[i];
		}
		sfjs->intensityScale = intensityScale;
	}
	sis->preFlag = preFlag;

	/* short blocks */
	if(sis->blockType == 2) {
		if(sis->mixedBlock) {
			/* do long block portion */
			for (sfb=0; sfb < 6; sfb++) {
				sfis->l[sfb] = (char)GetBits(bsi, slen[0]);
			}
			sfb = 3;  /* start sfb for short */
			nrIdx = 1;
		} else {      
			/* all short blocks, so start nr, sfb at 0 */
			sfb = 0;
			nrIdx = 0;
		}

		/* remaining short blocks, sfb just keeps incrementing */
		for (    ; nrIdx <= 3; nrIdx++) {
			for (i=0; i < nr[nrIdx]; i++, sfb++) {
				sfis->s[sfb][0] = (char)GetBits(bsi, slen[nrIdx]);
				sfis->s[sfb][1] = (char)GetBits(bsi, slen[nrIdx]);
				sfis->s[sfb][2] = (char)GetBits(bsi, slen[nrIdx]);
			}
		}
		/* last sf band not transmitted */
		sfis->s[12][0] = sfis->s[12][1] = sfis->s[12][2] = 0;
	} else {
		/* long blocks */
		sfb = 0;
		for (nrIdx = 0; nrIdx <= 3; nrIdx++) {
			for(i=0; i < nr[nrIdx]; i++, sfb++) {
				sfis->l[sfb] = (char)GetBits(bsi, slen[nrIdx]);
			}
		}
		/* last sf band not transmitted */
		sfis->l[21] = sfis->l[22] = 0;

	}
}

/**************************************************************************************
 * Function:    UnpackScaleFactors
 *
 * Description: parse the fields of the MP3 scale factor data section
 *
 * Inputs:      MP3DecInfo structure filled by UnpackFrameHeader() and UnpackSideInfo()
 *              buffer pointing to the MP3 scale factor data
 *              pointer to bit offset (0-7) indicating starting bit in buf[0]
 *              number of bits available in data buffer
 *              index of current granule and channel
 *
 * Outputs:     updated platform-specific ScaleFactorInfo struct
 *              updated bitOffset
 *
 * Return:      length (in bytes) of scale factor data, -1 if null input pointers
 **************************************************************************************/
int UnpackScaleFactors(MP3DecInfo *mp3DecInfo, unsigned char *buf, int *bitOffset, int bitsAvail, int gr, int ch)
{
	int bitsUsed;
	unsigned char *startBuf;
	BitStreamInfo bitStreamInfo, *bsi;
	FrameHeader *fh;
	SideInfo *si;
	ScaleFactorInfo *sfi;

	/* validate pointers */
	if (!mp3DecInfo || !mp3DecInfo->FrameHeaderPS || !mp3DecInfo->SideInfoPS || !mp3DecInfo->ScaleFactorInfoPS)
		return -1;
	fh = ((FrameHeader *)(mp3DecInfo->FrameHeaderPS));
	si = ((SideInfo *)(mp3DecInfo->SideInfoPS));
	sfi = ((ScaleFactorInfo *)(mp3DecInfo->ScaleFactorInfoPS));

	/* init GetBits reader */
	startBuf = buf;
	bsi = &bitStreamInfo;
	SetBitstreamPointer(bsi, (bitsAvail + *bitOffset + 7) / 8, buf);
	if (*bitOffset)
		GetBits(bsi, *bitOffset);

	if (fh->ver == MPEG1) 
		UnpackSFMPEG1(bsi, &si->sis[gr][ch], &sfi->sfis[gr][ch], si->scfsi[ch], gr, &sfi->sfis[0][ch]);
	else 
		UnpackSFMPEG2(bsi, &si->sis[gr][ch], &sfi->sfis[gr][ch], gr, ch, fh->modeExt, &sfi->sfjs);

	mp3DecInfo->part23Length[gr][ch] = si->sis[gr][ch].part23Length;

	bitsUsed = CalcBitsUsed(bsi, buf, *bitOffset);
	buf += (bitsUsed + *bitOffset) >> 3;
	*bitOffset = (bitsUsed + *bitOffset) & 0x07;

	return (buf - startBuf);
}