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发表于 2020-5-28 11:00:02
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显示全部楼层
void Encode(void)
{
int i, c, len, r, s, last_match_length, code_buf_ptr;
unsigned char code_buf[17], mask;
InitTree(); /* initialize trees */
code_buf[0] = 0; /* 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 p
air
(2 bytes). Thus, eight units require at most 16 bytes of co
de.
/
code_buf_ptr = mask = 1;
s = 0; r = N - F;
for (i = s; i < r; i++) text_buf[i] = ' '; /* Clear the buffer with
any character that will appear often. */
for (len = 0; len < F && (c = getc(infile)) != EOF; len++)
text_buf[r + len] = c; /* Read F bytes into the last F byte
s of
the buffer */
if ((textsize = len) == 0) return; /* text of size zero */
for (i = 1; i <= F; i++) InsertNode(r - i); /* Insert the F strings
,
each of which begins with one or more 'space' characters. N
ote
the order in which these strings are inserted. This way,
degenerate trees will be less likely to occur. */
InsertNode(r); /* Finally, insert the whole string just read. The
global variables match_length and match_position are set. */
do {
if (match_length > len) match_length = len; /* match_length
may be spuriously long near the end of text. */
if (match_length <= THRESHOLD) {
match_length = 1; /* Not long enough match. Send o
ne b
te. */
code_buf[0] |= mask; /* 'send one byte' flag */
code_buf[code_buf_ptr++] = text_buf[r]; /* Send unc
oded
*/
} else {
code_buf[code_buf_ptr++] = (unsigned char) match_pos
itio
;
code_buf[code_buf_ptr++] = (unsigned char)
(((match_position >> 4) & 0xf0)
| (match_length - (THRESHOLD + 1))); /* Send posi
tion
and
length pair. Note match_length > THR
ESHO
D. */
}
if ((mask <<= 1) == 0) { /* Shift mask left one bit. */
for (i = 0; i < code_buf_ptr; i++) /* Send at most
8 un
ts of */
putc(code_buf[i], outfile); /* code toge
ther
*/
codesize += code_buf_ptr;
code_buf[0] = 0; code_buf_ptr = mask = 1;
}
last_match_length = match_length;
for (i = 0; i < last_match_length &&
(c = getc(infile)) != EOF; i++) {
DeleteNode(s); /* Delete old strings and */
text_buf[s] = c; /* read new bytes */
if (s < F - 1) text_buf[s + N] = c; /* If the posit
ion
s
near the end of buffer, extend the buffer to
mak
string comparison easier. */
s = (s + 1) & (N - 1); r = (r + 1) & (N - 1);
/* Since this is a ring buffer, increment th
e po
ition
modulo N. */
InsertNode(r); /* Register the string in text_buf[r
..r+
-1] */
}
if ((textsize += i) > printcount) {
printf("%12ld\r", textsize); printcount += 1024;
/* Reports progress each time the textsize e
xcee
s
multiples of 1024. */
}
while (i++ < last_match_length) { /* After the end of
text
*/
DeleteNode(s); /* n
o ne
d to read, but */
s = (s + 1) & (N - 1); r = (r + 1) & (N - 1);
if (--len) InsertNode(r); /* buffer ma
y no
be empty. */
}
} while (len > 0); /* until length of string to be processed is
zer
*/
if (code_buf_ptr > 1) { /* Send remaining code. */
for (i = 0; i < code_buf_ptr; i++) putc(code_buf[i], outfile
);
codesize += code_buf_ptr;
}
printf("In : %ld bytes\n", textsize); /* Encoding is done. */
printf("Out: %ld bytes\n", codesize);
printf("Out/In: %.3f\n", (double)codesize / textsize);
}
void Decode(void) /* Just the reverse of Encode(). */
{
int i, j, k, r, c;
unsigned int flags;
for (i = 0; i < N - F; i++) text_buf[i] = ' ';
r = N - F; flags = 0;
for ( ; ; ) {
if (((flags >>= 1) & 256) == 0) {
if ((c = getc(infile)) == EOF) break;
flags = c | 0xff00; /* uses higher byte
clev
rly */
} /* t
o co
nt eight */
if (flags & 1) {
if ((c = getc(infile)) == EOF) break;
putc(c, outfile); text_buf[r++] = c; r &= (N - 1);
} else {
if ((i = getc(infile)) == EOF) break;
if ((j = getc(infile)) == EOF) break;
i |= ((j & 0xf0) << 4); j = (j & 0x0f) + THRESHOLD;
for (k = 0; k <= j; k++) {
c = text_buf[(i + k) & (N - 1)];
putc(c, outfile); text_buf[r++] = c; r &=
(N -
1);
}
}
}
}
int main(int argc, char *argv[])
{
char *s;
if (argc != 4) {
printf("'lzss e file1 file2' encodes file1 into file2.\n"
"'lzss d file2 file1' decodes file2 into file1.\n
");
return EXIT_FAILURE;
}
if ((s = argv[1], s[1] || strpbrk(s, "DEde") == NULL)
|| (s = argv[2], (infile = fopen(s, "rb")) == NULL)
|| (s = argv[3], (outfile = fopen(s, "wb")) == NULL)) {
printf("??? %s\n", s); return EXIT_FAILURE;
}
if (toupper(*argv[1]) == 'E') Encode(); else Decode();
fclose(infile); fclose(outfile);
return EXIT_SUCCESS;
}
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