readjpg.c

这是一个同样来自贝尔实验室的和UNIX有着渊源的操作系统, 其简洁的设计和实现易于我们学习和理解

				break;
			code <<= 1;
			m >>= 1;
			if(m == 0){
				t->shift[v] = 0;
				t->value[v] = -1;
				goto continueBytes;
			}
			cnt--;
		}
		t->shift[v] = 8-cnt;
		t->value[v] = t->val[t->valptr[i]+(code-t->mincode[i])];

    continueBytes:
		v++;
	}

	return nsize;
}

static
void
huffmantables(Header *h, uchar *b, int n)
{
	int l, mt;

	for(l=0; l<n; l+=17+mt)
		mt = huffmantable(h, &b[l]);
}

static
int
quanttable(Header *h, uchar *b)
{
	int i, pq, tq, *q;

	nibbles(b[0], &pq, &tq);
	if(pq > 1)
		jpgerror(h, "ReadJPG: unknown quantization table class %d", pq);
	if(tq > 3)
		jpgerror(h, "ReadJPG: unknown quantization table index %d", tq);
	q = h->qt[tq];
	for(i=0; i<64; i++){
		if(pq == 0)
			q[i] = b[1+i];
		else
			q[i] = int2(b, 1+2*i);
	}
	return 64*(1+pq);
}

static
void
quanttables(Header *h, uchar *b, int n)
{
	int l, m;

	for(l=0; l<n; l+=1+m)
		m = quanttable(h, &b[l]);
}

static
Rawimage*
baselinescan(Header *h, int colorspace)
{
	int Ns, z, k, m, Hmax, Vmax, comp;
	int allHV1, nblock, ri, mcu, nacross, nmcu;
	Huffman *dcht, *acht;
	int block, t, diff, *qt;
	uchar *ss;
	Rawimage *image;
	int Td[3], Ta[3], H[3], V[3], DC[3];
	int ***data, *zz;

	ss = h->ss;
	Ns = ss[0];
	if((Ns!=3 && Ns!=1) || Ns!=h->Nf)
		jpgerror(h, "ReadJPG: can't handle scan not 3 components");

	image = jpgmalloc(h, sizeof(Rawimage), 1);
	h->image = image;
	image->r = Rect(0, 0, h->X, h->Y);
	image->cmap = nil;
	image->cmaplen = 0;
	image->chanlen = h->X*h->Y;
	image->fields = 0;
	image->gifflags = 0;
	image->gifdelay = 0;
	image->giftrindex = 0;
	if(Ns == 3)
		image->chandesc = colorspace;
	else
		image->chandesc = CY;
	image->nchans = h->Nf;
	for(k=0; k<h->Nf; k++)
		image->chans[k] = jpgmalloc(h, h->X*h->Y, 0);

	/* compute maximum H and V */
	Hmax = 0;
	Vmax = 0;
	for(comp=0; comp<Ns; comp++){
		if(h->comp[comp].H > Hmax)
			Hmax = h->comp[comp].H;
		if(h->comp[comp].V > Vmax)
			Vmax = h->comp[comp].V;
	}

	/* initialize data structures */
	allHV1 = 1;
	data = h->data;
	for(comp=0; comp<Ns; comp++){
		/* JPEG requires scan components to be in same order as in frame, */
		/* so if both have 3 we know scan is Y Cb Cr and there's no need to */
		/* reorder */
		nibbles(ss[2+2*comp], &Td[comp], &Ta[comp]);
		H[comp] = h->comp[comp].H;
		V[comp] = h->comp[comp].V;
		nblock = H[comp]*V[comp];
		if(nblock != 1)
			allHV1 = 0;
		data[comp] = jpgmalloc(h, nblock*sizeof(int*), 0);
		h->ndata[comp] = nblock;
		DC[comp] = 0;
		for(m=0; m<nblock; m++)
			data[comp][m] = jpgmalloc(h, 8*8*sizeof(int), 0);
	}

	ri = h->ri;

	h->cnt = 0;
	h->sr = 0;
	h->peek = -1;
	nacross = ((h->X+(8*Hmax-1))/(8*Hmax));
	nmcu = ((h->Y+(8*Vmax-1))/(8*Vmax))*nacross;
	for(mcu=0; mcu<nmcu; ){
		for(comp=0; comp<Ns; comp++){
			dcht = &h->dcht[Td[comp]];
			acht = &h->acht[Ta[comp]];
			qt = h->qt[h->comp[comp].Tq];

			for(block=0; block<H[comp]*V[comp]; block++){
				/* F-22 */
				t = decode(h, dcht);
				diff = receive(h, t);
				DC[comp] += diff;

				/* F-23 */
				zz = data[comp][block];
				memset(zz, 0, 8*8*sizeof(int));
				zz[0] = qt[0]*DC[comp];
				k = 1;

				for(;;){
					t = decode(h, acht);
					if((t&0x0F) == 0){
						if((t&0xF0) != 0xF0)
							break;
						k += 16;
					}else{
						k += t>>4;
						z = receive(h, t&0xF);
						zz[zig[k]] = z*qt[k];
						if(k == 63)
							break;
						k++;
					}
				}

				idct(zz);
			}
		}

		/* rotate colors to RGB and assign to bytes */
		if(Ns == 1) /* very easy */
			colormap1(h, colorspace, image, data[0][0], mcu, nacross);
		else if(allHV1) /* fairly easy */
			colormapall1(h, colorspace, image, data[0][0], data[1][0], data[2][0], mcu, nacross);
		else /* miserable general case */
			colormap(h, colorspace, image, data[0], data[1], data[2], mcu, nacross, Hmax, Vmax, H, V);
		/* process restart marker, if present */
		mcu++;
		if(ri>0 && mcu<nmcu && mcu%ri==0){
			restart(h, mcu);
			for(comp=0; comp<Ns; comp++)
				DC[comp] = 0;
		}
	}
	return image;
}

static
void
restart(Header *h, int mcu)
{
	int rest, rst, nskip;

	rest = mcu/h->ri-1;
	nskip = 0;
	do{
		do{
			rst = nextbyte(h, 1);
			nskip++;
		}while(rst>=0 && rst!=0xFF);
		if(rst == 0xFF){
			rst = nextbyte(h, 1);
			nskip++;
		}
	}while(rst>=0 && (rst&~7)!=RST);
	if(nskip != 2)
		sprint(h->err, "ReadJPG: skipped %d bytes at restart %d\n", nskip-2, rest);
	if(rst < 0)
		jpgerror(h, readerr);
	if((rst&7) != (rest&7))
		jpgerror(h, "ReadJPG: expected RST%d got %d", rest&7, rst&7);
	h->cnt = 0;
	h->sr = 0;
}

static
Rawimage*
progressiveIDCT(Header *h, int colorspace)
{
	int k, m, comp, block, Nf, bn;
	int allHV1, nblock, mcu, nmcu;
	int H[3], V[3], blockno[3];
	int *dccoeff, **accoeff;
	int ***data, *zz;

	Nf = h->Nf;
	allHV1 = 1;
	data = h->data;

	for(comp=0; comp<Nf; comp++){
		H[comp] = h->comp[comp].H;
		V[comp] = h->comp[comp].V;
		nblock = h->nblock[comp];
		if(nblock != 1)
			allHV1 = 0;
		h->ndata[comp] = nblock;
		data[comp] = jpgmalloc(h, nblock*sizeof(int*), 0);
		for(m=0; m<nblock; m++)
			data[comp][m] = jpgmalloc(h, 8*8*sizeof(int), 0);
	}

	memset(blockno, 0, sizeof blockno);
	nmcu = h->nacross*h->ndown;
	for(mcu=0; mcu<nmcu; mcu++){
		for(comp=0; comp<Nf; comp++){
			dccoeff = h->dccoeff[comp];
			accoeff = h->accoeff[comp];
			bn = blockno[comp];
			for(block=0; block<h->nblock[comp]; block++){
				zz = data[comp][block];
				memset(zz, 0, 8*8*sizeof(int));
				zz[0] = dccoeff[bn];

				for(k=1; k<64; k++)
					zz[zig[k]] = accoeff[bn][k];

				idct(zz);
				bn++;
			}
			blockno[comp] = bn;
		}

		/* rotate colors to RGB and assign to bytes */
		if(Nf == 1) /* very easy */
			colormap1(h, colorspace, h->image, data[0][0], mcu, h->nacross);
		else if(allHV1) /* fairly easy */
			colormapall1(h, colorspace, h->image, data[0][0], data[1][0], data[2][0], mcu, h->nacross);
		else /* miserable general case */
			colormap(h, colorspace, h->image, data[0], data[1], data[2], mcu, h->nacross, h->Hmax, h->Vmax, H, V);
	}

	return h->image;
}

static
void
progressiveinit(Header *h, int colorspace)
{
	int Nf, Ns, j, k, nmcu, comp;
	uchar *ss;
	Rawimage *image;

	ss = h->ss;
	Ns = ss[0];
	Nf = h->Nf;
	if((Ns!=3 && Ns!=1) || Ns!=Nf)
		jpgerror(h, "ReadJPG: image must have 1 or 3 components");

	image = jpgmalloc(h, sizeof(Rawimage), 1);
	h->image = image;
	image->r = Rect(0, 0, h->X, h->Y);
	image->cmap = nil;
	image->cmaplen = 0;
	image->chanlen = h->X*h->Y;
	image->fields = 0;
	image->gifflags = 0;
	image->gifdelay = 0;
	image->giftrindex = 0;
	if(Nf == 3)
		image->chandesc = colorspace;
	else
		image->chandesc = CY;
	image->nchans = h->Nf;
	for(k=0; k<Nf; k++){
		image->chans[k] = jpgmalloc(h, h->X*h->Y, 0);
		h->nblock[k] = h->comp[k].H*h->comp[k].V;
	}

	/* compute maximum H and V */
	h->Hmax = 0;
	h->Vmax = 0;
	for(comp=0; comp<Nf; comp++){
		if(h->comp[comp].H > h->Hmax)
			h->Hmax = h->comp[comp].H;
		if(h->comp[comp].V > h->Vmax)
			h->Vmax = h->comp[comp].V;
	}
	h->nacross = ((h->X+(8*h->Hmax-1))/(8*h->Hmax));
	h->ndown = ((h->Y+(8*h->Vmax-1))/(8*h->Vmax));
	nmcu = h->nacross*h->ndown;

	for(k=0; k<Nf; k++){
		h->dccoeff[k] = jpgmalloc(h, h->nblock[k]*nmcu * sizeof(int), 1);
		h->accoeff[k] = jpgmalloc(h, h->nblock[k]*nmcu * sizeof(int*), 1);
		h->naccoeff[k] = h->nblock[k]*nmcu;
		for(j=0; j<h->nblock[k]*nmcu; j++)
			h->accoeff[k][j] = jpgmalloc(h, 64*sizeof(int), 1);
	}

}

static
void
progressivedc(Header *h, int comp, int Ah, int Al)
{
	int Ns, z, ri, mcu,  nmcu;
	int block, t, diff, qt, *dc, bn;
	Huffman *dcht;
	uchar *ss;
	int Td[3], DC[3], blockno[3];

	ss= h->ss;
	Ns = ss[0];
	if(Ns!=h->Nf)
		jpgerror(h, "ReadJPG: can't handle progressive with Nf!=Ns in DC scan");

	/* initialize data structures */
	h->cnt = 0;
	h->sr = 0;
	h->peek = -1;
	for(comp=0; comp<Ns; comp++){
		/*
		 * JPEG requires scan components to be in same order as in frame,
		 * so if both have 3 we know scan is Y Cb Cr and there's no need to
		 * reorder
		 */
		nibbles(ss[2+2*comp], &Td[comp], &z);	/* z is ignored */
		DC[comp] = 0;
	}

	ri = h->ri;

	nmcu = h->nacross*h->ndown;
	memset(blockno, 0, sizeof blockno);
	for(mcu=0; mcu<nmcu; ){
		for(comp=0; comp<Ns; comp++){
			dcht = &h->dcht[Td[comp]];
			qt = h->qt[h->comp[comp].Tq][0];
			dc = h->dccoeff[comp];
			bn = blockno[comp];

			for(block=0; block<h->nblock[comp]; block++){
				if(Ah == 0){
					t = decode(h, dcht);
					diff = receive(h, t);
					DC[comp] += diff;
					dc[bn] = qt*DC[comp]<<Al;
				}else
					dc[bn] |= qt*receivebit(h)<<Al;
				bn++;
			}
			blockno[comp] = bn;
		}

		/* process restart marker, if present */
		mcu++;
		if(ri>0 && mcu<nmcu && mcu%ri==0){
			restart(h, mcu);
			for(comp=0; comp<Ns; comp++)
				DC[comp] = 0;
		}
	}
}

static
void
progressiveac(Header *h, int comp, int Al)
{
	int Ns, Ss, Se, z, k, eobrun, x, y, nver, tmcu, blockno, *acc, rs;
	int ri, mcu, nacross, ndown, nmcu, nhor;
	Huffman *acht;
	int *qt, rrrr, ssss, q;
	uchar *ss;
	int Ta, H, V;

	ss = h->ss;
	Ns = ss[0];
	if(Ns != 1)
		jpgerror(h, "ReadJPG: illegal Ns>1 in progressive AC scan");
	Ss = ss[1+2];
	Se = ss[2+2];
	H = h->comp[comp].H;
	V = h->comp[comp].V;

	nacross = h->nacross*H;
	ndown = h->ndown*V;
	q = 8*h->Hmax/H;
	nhor = (h->X+q-1)/q;
	q = 8*h->Vmax/V;
	nver = (h->Y+q-1)/q;

	/* initialize data structures */
	h->cnt = 0;
	h->sr = 0;
	h->peek = -1;
	nibbles(ss[1+1], &z, &Ta);	/* z is thrown away */

	ri = h->ri;

	eobrun = 0;
	acht = &h->acht[Ta];
	qt = h->qt[h->comp[comp].Tq];
	nmcu = nacross*ndown;
	mcu = 0;
	for(y=0; y<nver; y++){
		for(x=0; x<nhor; x++){
			/* Figure G-3  */
			if(eobrun > 0){
				--eobrun;
				continue;
			}

			/* arrange blockno to be in same sequence as original scan calculation. */
			tmcu = x/H + (nacross/H)*(y/V);
			blockno = tmcu*H*V + H*(y%V) + x%H;
			acc = h->accoeff[comp][blockno];
			k = Ss;
			for(;;){
				rs = decode(h, acht);
				/* XXX remove rrrr ssss as in baselinescan */
				nibbles(rs, &rrrr, &ssss);
				if(ssss == 0){
					if(rrrr < 15){
						eobrun = 0;
						if(rrrr > 0)
							eobrun = receiveEOB(h, rrrr)-1;
						break;
					}
					k += 16;
				}else{
					k += rrrr;
					z = receive(h, ssss);
					acc[k] = z*qt[k]<<Al;
					if(k == Se)
						break;
					k++;
				}
			}
		}

		/* process restart marker, if present */
		mcu++;
		if(ri>0 && mcu<nmcu && mcu%ri==0){
			restart(h, mcu);
			eobrun = 0;
		}
	}
}

static
void
increment(Header *h, int acc[], int k, int Pt)
{
	if(acc[k] == 0)
		return;
	if(receivebit(h) != 0)
		if(acc[k] < 0)
			acc[k] -= Pt;
		else
			acc[k] += Pt;
}

static
void
progressiveacinc(Header *h, int comp, int Al)
{
	int Ns, i, z, k, Ss, Se, Ta, **ac, H, V;
	int ri, mcu, nacross, ndown, nhor, nver, eobrun, nzeros, pending, x, y, tmcu, blockno, q, nmcu;
	Huffman *acht;
	int *qt, rrrr, ssss, *acc, rs;
	uchar *ss;

	ss = h->ss;
	Ns = ss[0];
	if(Ns != 1)
		jpgerror(h, "ReadJPG: illegal Ns>1 in progressive AC scan");
	Ss = ss[1+2];
	Se = ss[2+2];
	H = h->comp[comp].H;
	V = h->comp[comp].V;

	nacross = h->nacross*H;
	ndown = h->ndown*V;
	q = 8*h->Hmax/H;
	nhor = (h->X+q-1)/q;
	q = 8*h->Vmax/V;
	nver = (h->Y+q-1)/q;

	/* initialize data structures */
	h->cnt = 0;
	h->sr = 0;
	h->peek = -1;
	nibbles(ss[1+1], &z, &Ta);	/* z is thrown away */
	ri = h->ri;

	eobrun = 0;
	ac = h->accoeff[comp];
	acht = &h->acht[Ta];
	qt = h->qt[h->comp[comp].Tq];
	nmcu = nacross*ndown;
	mcu = 0;
	pending = 0;
	nzeros = -1;
	for(y=0; y<nver; y++){
		for(x=0; x<nhor; x++){
			/* Figure G-7 */

			/*  arrange blockno to be in same sequence as original scan calculation. */
			tmcu = x/H + (nacross/H)*(y/V);
			blockno = tmcu*H*V + H*(y%V) + x%H;
			acc = ac[blockno];
			if(eobrun > 0){
				if(nzeros > 0)
					jpgerror(h, "ReadJPG: zeros pending at block start");
				for(k=Ss; k<=Se; k++)
					increment(h, acc, k, qt[k]<<Al);
				--eobrun;
				continue;
			}

			for(k=Ss; k<=Se; ){