# mkext.c   [plain text]

```/*
* Copyright (c) 2000-2004 Apple Computer, Inc. All rights reserved.
*
* @APPLE_OSREFERENCE_LICENSE_HEADER_START@
*
* This file contains Original Code and/or Modifications of Original Code
* as defined in and that are subject to the Apple Public Source License
* Version 2.0 (the 'License'). You may not use this file except in
* compliance with the License. The rights granted to you under the License
* may not be used to create, or enable the creation or redistribution of,
* unlawful or unlicensed copies of an Apple operating system, or to
* circumvent, violate, or enable the circumvention or violation of, any
* terms of an Apple operating system software license agreement.
*
* Please obtain a copy of the License at
* http://www.opensource.apple.com/apsl/ and read it before using this file.
*
* The Original Code and all software distributed under the License are
* distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER
* EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
* INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT.
* Please see the License for the specific language governing rights and
* limitations under the License.
*
* @APPLE_OSREFERENCE_LICENSE_HEADER_END@
*/
#include <string.h>
#include <libkern/mkext.h>

#define BASE 65521L /* largest prime smaller than 65536 */
#define NMAX 5000
// NMAX (was 5521) the largest n such that 255n(n+1)/2 + (n+1)(BASE-1) <= 2^32-1

#define DO1(buf,i)  {s1 += buf[i]; s2 += s1;}
#define DO2(buf,i)  DO1(buf,i); DO1(buf,i+1);
#define DO4(buf,i)  DO2(buf,i); DO2(buf,i+2);
#define DO8(buf,i)  DO4(buf,i); DO4(buf,i+4);
#define DO16(buf)   DO8(buf,0); DO8(buf,8);

u_int32_t
mkext_adler32(uint8_t *buf, int32_t len)
{
unsigned long s1 = 1; // adler & 0xffff;
unsigned long s2 = 0; // (adler >> 16) & 0xffff;
int k;

while (len > 0) {
k = len < NMAX ? len : NMAX;
len -= k;
while (k >= 16) {
DO16(buf);
buf += 16;
k -= 16;
}
if (k != 0) do {
s1 += *buf++;
s2 += s1;
} while (--k);
s1 %= BASE;
s2 %= BASE;
}
return (s2 << 16) | s1;
}

/**************************************************************
LZSS.C -- A Data Compression Program
***************************************************************
4/6/1989 Haruhiko Okumura
Use, distribute, and modify this program freely.
Please send me your improved versions.
PC-VAN      SCIENCE
NIFTY-Serve PAF01022
CompuServe  74050,1022

**************************************************************/

#define N         4096  /* size of ring buffer - must be power of 2 */
#define F         18    /* upper limit for match_length */
#define THRESHOLD 2     /* encode string into position and length
if match_length is greater than this */
#define NIL       N     /* index for root of binary search trees */

struct encode_state {
/*
* left & right children & parent. These constitute binary search trees.
*/
int lchild[N + 1], rchild[N + 257], parent[N + 1];

/* ring buffer of size N, with extra F-1 bytes to aid string comparison */
u_int8_t text_buf[N + F - 1];

/*
* match_length of longest match.
* These are set by the insert_node() procedure.
*/
int match_position, match_length;
};

int
decompress_lzss(u_int8_t *dst, u_int32_t dstlen, u_int8_t *src, u_int32_t srclen)
{
/* ring buffer of size N, with extra F-1 bytes to aid string comparison */
u_int8_t text_buf[N + F - 1];
u_int8_t *dststart = dst;
u_int8_t *dstend = dst + dstlen;
u_int8_t *srcend = src + srclen;
int  i, j, k, r, c;
unsigned int flags;

dst = dststart;
srcend = src + srclen;
for (i = 0; i < N - F; i++)
text_buf[i] = ' ';
r = N - F;
flags = 0;
for ( ; ; ) {
if (((flags >>= 1) & 0x100) == 0) {
if (src < srcend) c = *src++; else break;
flags = c | 0xFF00;  /* uses higher byte cleverly */
}   /* to count eight */
if (flags & 1) {
if (src < srcend) c = *src++; else break;
*dst++ = c;
if (dst >= dstend) {
goto finish;
}
text_buf[r++] = c;
r &= (N - 1);
} else {
if (src < srcend) i = *src++; else break;
if (src < srcend) j = *src++; else break;
i |= ((j & 0xF0) << 4);
j  =  (j & 0x0F) + THRESHOLD;
for (k = 0; k <= j; k++) {
c = text_buf[(i + k) & (N - 1)];
*dst++ = c;
if (dst >= dstend) {
goto finish;
}
text_buf[r++] = c;
r &= (N - 1);
}
}
}
finish:
return dst - dststart;
}

#if !KERNEL

/*
* initialize state, mostly the trees
*
* For i = 0 to N - 1, rchild[i] and lchild[i] will be the right and left
* children of node i.  These nodes need not be initialized.  Also, parent[i]
* is the parent of node i.  These are initialized to NIL (= N), which stands
* for 'not used.'  For i = 0 to 255, rchild[N + i + 1] is the root of the
* tree for strings that begin with character i.  These are initialized to NIL.
* Note there are 256 trees. */
static void init_state(struct encode_state *sp)
{
int  i;

bzero(sp, sizeof(*sp));

for (i = 0; i < N - F; i++)
sp->text_buf[i] = ' ';
for (i = N + 1; i <= N + 256; i++)
sp->rchild[i] = NIL;
for (i = 0; i < N; i++)
sp->parent[i] = NIL;
}

/*
* Inserts string of length F, text_buf[r..r+F-1], into one of the trees
* (text_buf[r]'th tree) and returns the longest-match position and length
* via the global variables match_position and match_length.
* If match_length = F, then removes the old node in favor of the new one,
* because the old one will be deleted sooner. Note r plays double role,
* as tree node and position in buffer.
*/
static void insert_node(struct encode_state *sp, int r)
{
int  i, p, cmp;
u_int8_t  *key;

cmp = 1;
key = &sp->text_buf[r];
p = N + 1 + key[0];
sp->rchild[r] = sp->lchild[r] = NIL;
sp->match_length = 0;
for ( ; ; ) {
if (cmp >= 0) {
if (sp->rchild[p] != NIL)
p = sp->rchild[p];
else {
sp->rchild[p] = r;
sp->parent[r] = p;
return;
}
} else {
if (sp->lchild[p] != NIL)
p = sp->lchild[p];
else {
sp->lchild[p] = r;
sp->parent[r] = p;
return;
}
}
for (i = 1; i < F; i++) {
if ((cmp = key[i] - sp->text_buf[p + i]) != 0)
break;
}
if (i > sp->match_length) {
sp->match_position = p;
if ((sp->match_length = i) >= F)
break;
}
}
sp->parent[r] = sp->parent[p];
sp->lchild[r] = sp->lchild[p];
sp->rchild[r] = sp->rchild[p];
sp->parent[sp->lchild[p]] = r;
sp->parent[sp->rchild[p]] = r;
if (sp->rchild[sp->parent[p]] == p)
sp->rchild[sp->parent[p]] = r;
else
sp->lchild[sp->parent[p]] = r;
sp->parent[p] = NIL;  /* remove p */
}

/* deletes node p from tree */
static void delete_node(struct encode_state *sp, int p)
{
int  q;

if (sp->parent[p] == NIL)
return;  /* not in tree */
if (sp->rchild[p] == NIL)
q = sp->lchild[p];
else if (sp->lchild[p] == NIL)
q = sp->rchild[p];
else {
q = sp->lchild[p];
if (sp->rchild[q] != NIL) {
do {
q = sp->rchild[q];
} while (sp->rchild[q] != NIL);
sp->rchild[sp->parent[q]] = sp->lchild[q];
sp->parent[sp->lchild[q]] = sp->parent[q];
sp->lchild[q] = sp->lchild[p];
sp->parent[sp->lchild[p]] = q;
}
sp->rchild[q] = sp->rchild[p];
sp->parent[sp->rchild[p]] = q;
}
sp->parent[q] = sp->parent[p];
if (sp->rchild[sp->parent[p]] == p)
sp->rchild[sp->parent[p]] = q;
else
sp->lchild[sp->parent[p]] = q;
sp->parent[p] = NIL;
}

#endif /* !KERNEL */

```