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75 lines
1.8 KiB
C
75 lines
1.8 KiB
C
1 year ago
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/* LZSS encoder-decoder (Haruhiko Okumura; public domain) */
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/* Modified by Clyne Sullivan to focus on streamed decompression. */
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#ifndef EOF
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#define EOF (-1)
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#endif
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#define EI 8 /* typically 10..13 */
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#define EJ 3 /* typically 4..5 */
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#define N (1 << EI) /* buffer size */
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#define F ((1 << EJ) + 1) /* lookahead buffer size */
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static unsigned char buffer[N * 2];
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static const unsigned char *inbuffer;
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static unsigned int insize, inidx;
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static int buf, mask;
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/* Prepares decode() to decompress the given data. */
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void lzssinit(const unsigned char *inb, unsigned int ins)
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{
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inbuffer = inb;
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insize = ins;
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inidx = 0;
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buf = 0;
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mask = 0;
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}
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int getbit(int n) /* get n bits */
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{
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int i, x;
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x = 0;
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for (i = 0; i < n; i++) {
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if (mask == 0) {
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if (inidx >= insize)
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return EOF;
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buf = inbuffer[inidx++];
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mask = 128;
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}
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x <<= 1;
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if (buf & mask) x++;
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mask >>= 1;
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}
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return x;
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}
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/* handleoutput() receives each decompressed byte, return zero if want more. */
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int decode(int (*handleoutput)(int))
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{
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int i, j, k, r, c, ret;
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for (i = 0; i < N - F; i++) buffer[i] = ' ';
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r = N - F;
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while ((c = getbit(1)) != EOF) {
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if (c) {
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if ((c = getbit(8)) == EOF) break;
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if ((ret = handleoutput(c)))
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return ret;
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buffer[r++] =(unsigned char) c; r &= (N - 1);
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} else {
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if ((i = getbit(EI)) == EOF) break;
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if ((j = getbit(EJ)) == EOF) break;
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for (k = 0; k <= j + 1; k++) {
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c = buffer[(i + k) & (N - 1)];
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if ((ret = handleoutput(c)))
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return ret;
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buffer[r++] = (unsigned char)c; r &= (N - 1);
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}
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}
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}
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return EOF;
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}
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