/************************************************************** LZSS.C -- A Data Compression Program (tab = 4 spaces) *************************************************************** 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 **************************************************************/ #include <stdio.h> #include <stdlib.h> #include <string.h> #include <ctype.h> #define N 4096 /* size of ring buffer */ #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 */ unsigned long int textsize = 0, /* text size counter */ codesize = 0, /* code size counter */ printcount = 0; /* counter for reporting progress every 1K bytes */ unsigned char text_buf[N + F - 1]; /* ring buffer of size N, with extra F-1 bytes to facilitate string comparison */ int match_position, match_length, /* of longest match. These are set by the InsertNode() procedure. */ lson[N + 1], rson[N + 257], dad[N + 1]; /* left & right children & parents -- These constitute binary search trees. */ FILE *infile, *outfile; /* input & output files */ void InitTree(void) /* initialize trees */ { int i; /* For i = 0 to N - 1, rson[i] and lson[i] will be the right and left children of node i. These nodes need not be initialized. Also, dad[i] is the parent of node i. These are initialized to NIL (= N), which stands for 'not used.' For i = 0 to 255, rson[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. */ for (i = N + 1; i <= N + 256; i++) rson[i] = NIL; for (i = 0; i < N; i++) dad[i] = NIL; } void InsertNode(int r) /* 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. */ { int i, p, cmp; unsigned char *key; cmp = 1; key = &text_buf[r]; p = N + 1 + key[0]; rson[r] = lson[r] = NIL; match_length = 0; for ( ; ; ) { if (cmp >= 0) { if (rson[p] != NIL) p = rson[p]; else { rson[p] = r; dad[r] = p; return; } } else { if (lson[p] != NIL) p = lson[p]; else { lson[p] = r; dad[r] = p; return; } } for (i = 1; i < F; i++) if ((cmp = key[i] - text_buf[p + i]) != 0) break; if (i > match_length) { match_position = p; if ((match_length = i) >= F) break; } } dad[r] = dad[p]; lson[r] = lson[p]; rson[r] = rson[p]; dad[lson[p]] = r; dad[rson[p]] = r; if (rson[dad[p]] == p) rson[dad[p]] = r; else lson[dad[p]] = r; dad[p] = NIL; /* remove p */ } void DeleteNode(int p) /* deletes node p from tree */ { int q; if (dad[p] == NIL) return; /* not in tree */ if (rson[p] == NIL) q = lson[p]; else if (lson[p] == NIL) q = rson[p]; else { q = lson[p]; if (rson[q] != NIL) { do { q = rson[q]; } while (rson[q] != NIL); rson[dad[q]] = lson[q]; dad[lson[q]] = dad[q]; lson[q] = lson[p]; dad[lson[p]] = q; } rson[q] = rson[p]; dad[rson[p]] = q; } dad[q] = dad[p]; if (rson[dad[p]] == p) rson[dad[p]] = q; else lson[dad[p]] = q; dad[p] = NIL; } 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 pair (2 bytes). Thus, eight units require at most 16 bytes of code. */ 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 bytes 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. Note 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 one byte. */ code_buf[0] |= mask; /* 'send one byte' flag */ code_buf[code_buf_ptr++] = text_buf[r]; /* Send uncoded. */ } else { code_buf[code_buf_ptr++] = (unsigned char) match_position; code_buf[code_buf_ptr++] = (unsigned char) (((match_position >> 4) & 0xf0) | (match_length - (THRESHOLD + 1))); /* Send position and length pair. Note match_length > THRESHOLD. */ } if ((mask <<= 1) == 0) { /* Shift mask left one bit. */ for (i = 0; i < code_buf_ptr; i++) /* Send at most 8 units of */ putc(code_buf[i], outfile); /* code together */ 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 position is near the end of buffer, extend the buffer to make string comparison easier. */ s = (s + 1) & (N - 1); r = (r + 1) & (N - 1); /* Since this is a ring buffer, increment the position modulo N. */ InsertNode(r); /* Register the string in text_buf[r..r+F-1] */ } if ((textsize += i) > printcount) { printf("%12ld ", textsize); printcount += 1024; /* Reports progress each time the textsize exceeds multiples of 1024. */ } while (i++ < last_match_length) { /* After the end of text, */ DeleteNode(s); /* no need to read, but */ s = (s + 1) & (N - 1); r = (r + 1) & (N - 1); if (--len) InsertNode(r); /* buffer may not be empty. */ } } 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++) putc(code_buf[i], outfile); codesize += code_buf_ptr; } printf("In : %ld bytes ", textsize); /* Encoding is done. */ printf("Out: %ld bytes ", codesize); printf("Out/In: %.3f ", (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 cleverly */ } /* to count 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. " "'lzss d file2 file1' decodes file2 into file1. "); 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 ", s); return EXIT_FAILURE; } if (toupper(*argv[1]) == 'E') Encode(); else Decode(); fclose(infile); fclose(outfile); return EXIT_SUCCESS; }