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_int8_t *src, u_int32_t srclen)␊ |
{␊ |
|
␊ |
return dst - dststart;␊ |
}␊ |
␊ |
/*␊ |
* 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;␊ |
}␊ |
␊ |
u_int8_t *compress_lzss(␊ |
u_int8_t * dst,␊ |
u_int32_t dstlen,␊ |
u_int8_t * src,␊ |
u_int32_t srclen)␊ |
{␊ |
u_int8_t * result = NULL;␊ |
/* Encoding state, mostly tree but some current match stuff */␊ |
struct encode_state *sp;␊ |
int i, c, len, r, s, last_match_length, code_buf_ptr;␊ |
u_int8_t code_buf[17], mask;␊ |
u_int8_t * srcend = src + srclen;␊ |
u_int8_t *dstend = dst + dstlen;␊ |
/* initialize trees */␊ |
sp = (struct encode_state *) malloc(sizeof(*sp));␊ |
if (!sp) goto finish;␊ |
init_state(sp);␊ |
/*␊ |
* code_buf[1..16] saves eight units of code, and code_buf[0] works␊ |
* as eight flags, "1" representing that the unit is an unencoded␊ |
* letter (1 byte), "0" a position-and-length pair (2 bytes).␊ |
* Thus, eight units require at most 16 bytes of code.␊ |
*/␊ |
code_buf[0] = 0;␊ |
code_buf_ptr = mask = 1;␊ |
/* Clear the buffer with any character that will appear often. */␊ |
s = 0; r = N - F;␊ |
/* Read F bytes into the last F bytes of the buffer */␊ |
for (len = 0; len < F && src < srcend; len++)␊ |
sp->text_buf[r + len] = *src++;␊ |
if (!len)␊ |
goto finish;␊ |
/*␊ |
* Insert the F strings, each of which begins with one or more␊ |
* 'space' characters. Note the order in which these strings are␊ |
* inserted. This way, degenerate trees will be less likely to occur.␊ |
*/␊ |
for (i = 1; i <= F; i++)␊ |
insert_node(sp, r - i);␊ |
/*␊ |
* Finally, insert the whole string just read.␊ |
* The global variables match_length and match_position are set.␊ |
*/␊ |
insert_node(sp, r);␊ |
do {␊ |
/* match_length may be spuriously long near the end of text. */␊ |
if (sp->match_length > len)␊ |
sp->match_length = len;␊ |
if (sp->match_length <= THRESHOLD) {␊ |
sp->match_length = 1; /* Not long enough match. Send one byte. */␊ |
code_buf[0] |= mask; /* 'send one byte' flag */␊ |
code_buf[code_buf_ptr++] = sp->text_buf[r]; /* Send uncoded. */␊ |
} else {␊ |
/* Send position and length pair. Note match_length > THRESHOLD. */␊ |
code_buf[code_buf_ptr++] = (u_int8_t) sp->match_position;␊ |
code_buf[code_buf_ptr++] = (u_int8_t)␊ |
( ((sp->match_position >> 4) & 0xF0)␊ |
| (sp->match_length - (THRESHOLD + 1)) );␊ |
}␊ |
if ((mask <<= 1) == 0) { /* Shift mask left one bit. */␊ |
/* Send at most 8 units of code together */␊ |
for (i = 0; i < code_buf_ptr; i++)␊ |
if (dst < dstend)␊ |
*dst++ = code_buf[i];␊ |
else␊ |
goto finish;␊ |
code_buf[0] = 0;␊ |
code_buf_ptr = mask = 1;␊ |
}␊ |
last_match_length = sp->match_length;␊ |
for (i = 0; i < last_match_length && src < srcend; i++) {␊ |
delete_node(sp, s); /* Delete old strings and */␊ |
c = *src++;␊ |
sp->text_buf[s] = c; /* read new bytes */␊ |
/*␊ |
* If the position is near the end of buffer, extend the buffer␊ |
* to make string comparison easier.␊ |
*/␊ |
if (s < F - 1)␊ |
sp->text_buf[s + N] = c;␊ |
/* Since this is a ring buffer, increment the position modulo N. */␊ |
s = (s + 1) & (N - 1);␊ |
r = (r + 1) & (N - 1);␊ |
/* Register the string in text_buf[r..r+F-1] */␊ |
insert_node(sp, r);␊ |
}␊ |
while (i++ < last_match_length) {␊ |
delete_node(sp, s);␊ |
/* After the end of text, no need to read, */␊ |
s = (s + 1) & (N - 1);␊ |
r = (r + 1) & (N - 1);␊ |
/* but buffer may not be empty. */␊ |
if (--len)␊ |
insert_node(sp, r);␊ |
}␊ |
} while (len > 0); /* until length of string to be processed is zero */␊ |
if (code_buf_ptr > 1) { /* Send remaining code. */␊ |
for (i = 0; i < code_buf_ptr; i++)␊ |
if (dst < dstend)␊ |
*dst++ = code_buf[i];␊ |
else␊ |
goto finish;␊ |
}␊ |
result = dst;␊ |
finish:␊ |
if (sp) free(sp);␊ |
return result;␊ |
}␊ |