shithub: pdffs

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ref: 3d14c5f66a2485db6ba7e25393a72e5f142049b6
parent: d1a98f52a81b08b68e9cbb0e78c166f62c936690
author: Sigrid Solveig Haflínudóttir <ftrvxmtrx@gmail.com>
date: Sun Nov 22 14:29:36 EST 2020 

lzw filter


--- a/f_lzw.c
+++ b/f_lzw.c
@@ -2,6 +2,163 @@
 #include <libc.h>
 #include "pdf.h"
 
+typedef struct Pt Pt;
+typedef struct Tb Tb;
+
+struct Pt {
+	int o, sz;
+};
+
+struct Tb {
+	Pt *pt;
+	int npt;
+
+	uchar *p;
+	int max;
+	int off;
+
+	Pt pr;
+};
+
+static void
+tbclean(Tb *tb)
+{
+	int i;
+
+	tb->off = 256;
+	tb->npt = 258;
+
+	if(tb->p == nil){
+		tb->max = 1024;
+		tb->p = malloc(tb->max);
+	}
+	if(tb->pt == nil){
+		tb->pt = malloc(sizeof(Pt)*4096);
+		for(i = 0; i < 256; i++){
+			tb->p[i] = i;
+			tb->pt[i].o = i;
+			tb->pt[i].sz = 1;
+		}
+	}
+	memset(tb->pt+tb->npt, 0, sizeof(Pt)*(4096-tb->npt));
+}
+
+static int
+tbputc(Tb *tb, int c, Buffer *o)
+{
+	uchar *d;
+	Pt *pt;
+	int n;
+
+	if(tb->pt == nil)
+		tbclean(tb);
+
+	/* firt, make sure things will fit in */
+	if(tb->max <= tb->off*2){
+		tb->max = tb->off*4;
+		tb->p = realloc(tb->p, tb->max);
+	}
+
+	pt = &tb->pt[c];
+	if(pt->sz > 0){
+		d = tb->p + pt->o;
+		n = pt->sz;
+
+		if(tb->pr.sz > 0){
+			/* have prefix - insert another point */
+			pt = &tb->pt[tb->npt++];
+			pt->o = tb->off;
+			pt->sz = tb->pr.sz + 1;
+			memmove(tb->p + pt->o, tb->p + tb->pr.o, tb->pr.sz);
+			tb->p[pt->o + pt->sz - 1] = d[0];
+			tb->off += pt->sz;
+		}
+
+		/* update prefix */
+		tb->pr.o = d - tb->p;
+		tb->pr.sz = n;
+	}else{
+		pt = &tb->pt[tb->npt++];
+		pt->o = tb->off;
+		pt->sz = tb->pr.sz + 1;
+		memmove(tb->p + pt->o, tb->p + tb->pr.o, tb->pr.sz);
+		tb->p[pt->o + pt->sz - 1] = tb->p[tb->pr.o];
+		tb->off += pt->sz;
+
+		tb->pr.o = pt->o;
+		tb->pr.sz = pt->sz;
+
+		d = tb->p + pt->o;
+		n = pt->sz;
+	}
+
+	bufput(o, d, n);
+
+	if(tb->npt < 511)
+		return 9;
+	if(tb->npt < 1023)
+		return 10;
+	if(tb->npt < 2047)
+		return 11;
+	if(tb->npt < 4097)
+		return 12;
+
+	return -1;
+}
+
+static void
+tbfree(Tb *tb)
+{
+	free(tb->p);
+	free(tb->pt);
+	memset(tb, 0, sizeof(*tb));
+}
+
+static int
+flreadall(void *aux, Buffer *bi, Buffer *bo)
+{
+	int i, j, x, insz, width, w;
+	uchar *in;
+	Tb tb;
+
+	USED(aux);
+
+	memset(&tb, 0, sizeof(tb));
+	in = bufdata(bi, &insz);
+	width = 9;
+	x = 0;
+	for(i = w = 0, j = 7; i < insz; j--){
+		x = x<<1 | ((in[i] & (1<<j)) >> j);
+		if(j < 1){
+			i++;
+			j = 8;
+		}
+
+		if(++w == width){
+			if(x == 257) /* EOD */
+				break;
+
+			if(x == 256){ /* CLEAR */
+				tbclean(&tb);
+				width = 9;
+			}else if((width = tbputc(&tb, x, bo)) < 0){
+				werrstr("points overflow");
+				tbfree(&tb);
+				return -1;
+			}
+
+			w = 0;
+			x = 0;
+		}
+	}
+
+	tbfree(&tb);
+	bi->off = bi->sz;
+
+	return 0;
+}
+
 Filter filterLZW = {
 	.name = "LZWDecode",
+	.readall = flreadall,
 };
-- 
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