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/*---------------------------------------------------------------------------
unshrink.c
Shrinking is a Dynamic Lempel-Ziv-Welch compression algorithm with partial
clearing.
---------------------------------------------------------------------------*/
#include "unz.h"
void flush_stack (int);
/*************************************/
/* UnShrink Defines, Globals, etc. */
/*************************************/
/* MAX_BITS 13 (in unzip.h; defines size of global work area) */
#define INIT_BITS 9
#define FIRST_ENT 257
#define CLEAR 256
#define GetCode(dest) READBIT(codesize,dest)
static void partial_clear ();
int codesize, maxcode, maxcodemax, free_ent;
/*************************/
/* Function unShrink() */
/*************************/
void unShrink()
{
register int code;
register int stackp;
int finchar;
int oldcode;
int incode;
/* decompress the file */
codesize = INIT_BITS;
maxcode = (1 << codesize) - 1;
maxcodemax = HSIZE; /* (1 << MAX_BITS) */
free_ent = FIRST_ENT;
code = maxcodemax;
do {
prefix_of[code] = -1;
} while (--code > 255);
/*
OvdL: -Ox with SCO's 3.2.0 cc gives
a. warning: overflow in constant multiplication
b. segmentation fault (core dumped) when using the executable
for (code = maxcodemax; code > 255; code--)
prefix_of[code] = -1;
*/
for (code = 255; code >= 0; code--) {
prefix_of[code] = 0;
suffix_of[code] = (byte) code;
}
GetCode(oldcode);
if (zipeof)
return;
finchar = oldcode;
stack[0] = finchar;
flush_stack (1);
stackp = HSIZE;
while (!zipeof) {
GetCode(code);
if (zipeof)
return;
while (code == CLEAR) {
GetCode(code);
switch (code) {
case 1:
codesize++;
if (codesize == MAX_BITS)
maxcode = maxcodemax;
else
maxcode = (1 << codesize) - 1;
break;
case 2:
partial_clear();
break;
}
GetCode(code);
if (zipeof)
return;
}
/* special case for KwKwK string */
incode = code;
if (prefix_of[code] == -1) {
stack[--stackp] = (byte) finchar;
code = oldcode;
}
/* generate output characters in reverse order */
while (code >= FIRST_ENT) {
if (prefix_of[code] == -1) {
stack[--stackp] = (byte) finchar;
code = oldcode;
} else {
stack[--stackp] = suffix_of[code];
code = prefix_of[code];
}
}
finchar = suffix_of[code];
stack[--stackp] = (byte) finchar;
/* and put them out in forward order, block copy */
flush_stack (HSIZE - stackp);
stackp = HSIZE;
/* generate new entry */
code = free_ent;
if (code < maxcodemax) {
prefix_of[code] = oldcode;
suffix_of[code] = (byte) finchar;
do
code++;
while ((code < maxcodemax) && (prefix_of[code] != -1));
free_ent = code;
}
/* remember previous code */
oldcode = incode;
}
}
/******************************/
/* Function partial_clear() */
/******************************/
static void partial_clear()
{
register int pr;
register int cd;
/* mark all nodes as potentially unused */
for (cd = FIRST_ENT; cd < free_ent; cd++)
prefix_of[cd] |= 0x8000;
/* unmark those that are used by other nodes */
for (cd = FIRST_ENT; cd < free_ent; cd++) {
pr = prefix_of[cd] & 0x7fff; /* reference to another node? */
if (pr >= FIRST_ENT) /* flag node as referenced */
prefix_of[pr] &= 0x7fff;
}
/* clear the ones that are still marked */
for (cd = FIRST_ENT; cd < free_ent; cd++)
if ((prefix_of[cd] & 0x8000) != 0)
prefix_of[cd] = -1;
/* find first cleared node as next free_ent */
cd = FIRST_ENT;
while ((cd < maxcodemax) && (prefix_of[cd] != -1))
cd++;
free_ent = cd;
}
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