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#include <u.h>
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#include <libc.h>
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#include <draw.h>
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#include <memdraw.h>
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#define	CHUNK	8000
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#define	HSHIFT	3	/* HSHIFT==5 runs slightly faster, but hash table is 64x bigger */
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#define	NHASH	(1<<(HSHIFT*NMATCH))
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#define	HMASK	(NHASH-1)
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#define	hupdate(h, c)	((((h)<<HSHIFT)^(c))&HMASK)
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typedef struct Hlist Hlist;
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struct Hlist{
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	uchar *s;
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	Hlist *next, *prev;
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};
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int
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writememimage(int fd, Memimage *i)
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{
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	uchar *outbuf, *outp, *eout;		/* encoded data, pointer, end */
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	uchar *loutp;				/* start of encoded line */
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	Hlist *hash;				/* heads of hash chains of past strings */
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	Hlist *chain, *hp;			/* hash chain members, pointer */
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	Hlist *cp;				/* next Hlist to fall out of window */
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	int h;					/* hash value */
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	uchar *line, *eline;			/* input line, end pointer */
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	uchar *data, *edata;			/* input buffer, end pointer */
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	ulong n;				/* length of input buffer */
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	ulong nb;				/* # of bytes returned by unloadimage */
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	int bpl;				/* input line length */
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	int offs, runlen;			/* offset, length of consumed data */
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	uchar dumpbuf[NDUMP];			/* dump accumulator */
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	int ndump;				/* length of dump accumulator */
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	int miny, dy;				/* y values while unloading input */
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	int ncblock;				/* size of compressed blocks */
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	Rectangle r;
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	uchar *p, *q, *s, *es, *t;
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	char hdr[11+5*12+1];
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	char cbuf[20];
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	r = i->r;
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	bpl = bytesperline(r, i->depth);
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	n = Dy(r)*bpl;
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	data = malloc(n);
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	ncblock = _compblocksize(r, i->depth);
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	outbuf = malloc(ncblock);
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	hash = malloc(NHASH*sizeof(Hlist));
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	chain = malloc(NMEM*sizeof(Hlist));
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	if(data == 0 || outbuf == 0 || hash == 0 || chain == 0){
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	ErrOut:
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		free(data);
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		free(outbuf);
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		free(hash);
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		free(chain);
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		return -1;
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	}
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	for(miny = r.min.y; miny != r.max.y; miny += dy){
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		dy = r.max.y-miny;
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		if(dy*bpl > CHUNK)
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			dy = CHUNK/bpl;
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		nb = unloadmemimage(i, Rect(r.min.x, miny, r.max.x, miny+dy),
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			data+(miny-r.min.y)*bpl, dy*bpl);
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		if(nb != dy*bpl)
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			goto ErrOut;
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	}
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	sprint(hdr, "compressed\n%11s %11d %11d %11d %11d ",
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		chantostr(cbuf, i->chan), r.min.x, r.min.y, r.max.x, r.max.y);
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	if(write(fd, hdr, 11+5*12) != 11+5*12)
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		goto ErrOut;
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	edata = data+n;
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	eout = outbuf+ncblock;
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	line = data;
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	r.max.y = r.min.y;
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	while(line != edata){
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		memset(hash, 0, NHASH*sizeof(Hlist));
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		memset(chain, 0, NMEM*sizeof(Hlist));
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		cp = chain;
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		h = 0;
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		outp = outbuf;
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		for(n = 0; n != NMATCH; n++)
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			h = hupdate(h, line[n]);
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		loutp = outbuf;
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		while(line != edata){
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			ndump = 0;
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			eline = line+bpl;
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			for(p = line; p != eline; ){
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				if(eline-p < NRUN)
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					es = eline;
90 
				else
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					es = p+NRUN;
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				q = 0;
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				runlen = 0;
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				for(hp = hash[h].next; hp; hp = hp->next){
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					s = p + runlen;
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					if(s >= es)
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						continue;
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					t = hp->s + runlen;
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					for(; s >= p; s--)
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						if(*s != *t--)
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							goto matchloop;
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					t += runlen+2;
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					s += runlen+2;
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					for(; s < es; s++)
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						if(*s != *t++)
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							break;
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					n = s-p;
108 
					if(n > runlen){
109 
						runlen = n;
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						q = hp->s;
111 
						if(n == NRUN)
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							break;
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					}
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			matchloop: ;
115 
				}
116 
				if(runlen < NMATCH){
117 
					if(ndump == NDUMP){
118 
						if(eout-outp < ndump+1)
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							goto Bfull;
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						*outp++ = ndump-1+128;
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						memmove(outp, dumpbuf, ndump);
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						outp += ndump;
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						ndump = 0;
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					}
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					dumpbuf[ndump++] = *p;
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					runlen = 1;
127 
				}
128 
				else{
129 
					if(ndump != 0){
130 
						if(eout-outp < ndump+1)
131 
							goto Bfull;
132 
						*outp++ = ndump-1+128;
133 
						memmove(outp, dumpbuf, ndump);
134 
						outp += ndump;
135 
						ndump = 0;
136 
					}
137 
					offs = p-q-1;
138 
					if(eout-outp < 2)
139 
						goto Bfull;
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					*outp++ = ((runlen-NMATCH)<<2) + (offs>>8);
141 
					*outp++ = offs&255;
142 
				}
143 
				for(q = p+runlen; p != q; p++){
144 
					if(cp->prev)
145 
						cp->prev->next = 0;
146 
					cp->next = hash[h].next;
147 
					cp->prev = &hash[h];
148 
					if(cp->next)
149 
						cp->next->prev = cp;
150 
					cp->prev->next = cp;
151 
					cp->s = p;
152 
					if(++cp == &chain[NMEM])
153 
						cp = chain;
154 
					if(edata-p > NMATCH)
155 
						h = hupdate(h, p[NMATCH]);
156 
				}
157 
			}
158 
			if(ndump != 0){
159 
				if(eout-outp < ndump+1)
160 
					goto Bfull;
161 
				*outp++ = ndump-1+128;
162 
				memmove(outp, dumpbuf, ndump);
163 
				outp += ndump;
164 
			}
165 
			line = eline;
166 
			loutp = outp;
167 
			r.max.y++;
168 
		}
169 
	Bfull:
170 
		if(loutp == outbuf)
171 
			goto ErrOut;
172 
		n = loutp-outbuf;
173 
		sprint(hdr, "%11d %11ld ", r.max.y, n);
174 
		write(fd, hdr, 2*12);
175 
		write(fd, outbuf, n);
176 
		r.min.y = r.max.y;
177 
	}
178 
	free(data);
179 
	free(outbuf);
180 
	free(hash);
181 
	free(chain);
182 
	return 0;
183 
}