1 /***************************************************************************
2 *
3 * GIFENCOD.C - GIF Image compression routines
4 *
5 * Lempel-Ziv compression based on 'compress'. GIF modifications by
6 * David Rowley (mgardi@watdcsu.waterloo.edu)
7 *
8 ***************************************************************************/
9
10 /*
11 * General DEFINEs
12 */
13 #define GIFBITS 12
14 #define MSDOS 1
15
16 #define HSIZE 5003 /* 80% occupancy */
17
18 /*
19 * a code_int must be able to hold 2**GIFBITS values of type int, and also -1
20 */
21 typedef int code_int;
22
23 #ifdef SIGNED_COMPARE_SLOW
24 typedef unsigned long int count_int;
25 typedef unsigned short int count_short;
26 #else
27 typedef long int count_int;
28 #endif
29
30 #ifdef NO_UCHAR
31 typedef char char_type;
32 #else
33 typedef unsigned char char_type;
34 #endif /* UCHAR */
35
36 /*
37 *
38 * GIF Image compression - modified 'compress'
39 *
40 * Based on: compress.c - File compression ala IEEE Computer, June 1984.
41 *
42 * By Authors: Spencer W. Thomas (decvax!harpo!utah-cs!utah-gr!thomas)
43 * Jim McKie (decvax!mcvax!jim)
44 * Steve Davies (decvax!vax135!petsd!peora!srd)
45 * Ken Turkowski (decvax!decwrl!turtlevax!ken)
46 * James A. Woods (decvax!ihnp4!ames!jaw)
47 * Joe Orost (decvax!vax135!petsd!joe)
48 *
49 */
50 #include <lug.h>
51 #include <lugfnts.h>
52 #include <ctype.h>
53
54 static output();
55 static cl_block();
56 static cl_hash();
57 static writeerr();
58 static char_init();
59 static char_out();
60 static flush_char();
61
62 static int n_bits; /* number of bits/code */
63 static int maxbits = GIFBITS; /* user settable max # bits/code */
64 static code_int maxcode; /* maximum code, given n_bits */
65 static code_int maxmaxcode = (code_int)1 << GIFBITS; /* should NEVER generate this code */
66 #ifdef COMPATIBLE /* But wrong! */
67 # define MAXCODE(n_bits) ((code_int) 1 << (n_bits) - 1)
68 #else
69 # define MAXCODE(n_bits) (((code_int) 1 << (n_bits)) - 1)
70 #endif /* COMPATIBLE */
71
72 static count_int htab [HSIZE];
73 static unsigned short codetab [HSIZE];
74 #define HashTabOf(i) htab[i]
75 #define CodeTabOf(i) codetab[i]
76
77 static code_int hsize = HSIZE; /* for dynamic table sizing */
78 static count_int fsize;
79
80 /*
81 * To save much memory, we overlay the table used by compress() with those
82 * used by decompress(). The tab_prefix table is the same size and type
83 * as the codetab. The tab_suffix table needs 2**GIFBITS characters. We
84 * get this from the beginning of htab. The output stack uses the rest
85 * of htab, and contains characters. There is plenty of room for any
86 * possible stack (stack used to be 8000 characters).
87 */
88
89 #define tab_prefixof(i) CodeTabOf(i)
90 #define tab_suffixof(i) ((char_type *)(htab))[i]
91 #define de_stack ((char_type *)&tab_suffixof((code_int)1<<GIFBITS))
92
93 static code_int free_ent = 0; /* first unused entry */
94 static int exit_stat = 0;
95
96 /*
97 * block compression parameters -- after all codes are used up,
98 * and compression rate changes, start over.
99 */
100 static int clear_flg = 0;
101
102 static int offset;
103 static long int in_count = 1; /* length of input */
104 static long int out_count = 0; /* # of codes output (for debugging) */
105
106 /*
107 * compress stdin to stdout
108 *
109 * Algorithm: use open addressing double hashing (no chaining) on the
110 * prefix code / next character combination. We do a variant of Knuth's
111 * algorithm D (vol. 3, sec. 6.4) along with G. Knott's relatively-prime
112 * secondary probe. Here, the modular division first probe is gives way
113 * to a faster exclusive-or manipulation. Also do block compression with
114 * an adaptive reset, whereby the code table is cleared when the compression
115 * ratio decreases, but after the table fills. The variable-length output
116 * codes are re-sized at this point, and a special CLEAR code is generated
117 * for the decompressor. Late addition: construct the table according to
118 * file size for noticeable speed improvement on small files. Please direct
119 * questions about this implementation to ames!jaw.
120 */
121
122 static int g_init_bits;
123 static FILE *g_outfile;
124
125 static int ClearCode;
126 static int EOFCode;
127
compress(init_bits,outfile,ReadValue)128 compress( init_bits, outfile, ReadValue )
129 int init_bits;
130 FILE *outfile;
131 ifunptr ReadValue;
132 {
133 register long fcode;
134 register code_int i = 0;
135 register int c;
136 register code_int ent;
137 register code_int disp;
138 register code_int hsize_reg;
139 register int hshift;
140
141 /*
142 * Set up the globals: g_init_bits - initial number of bits
143 * g_outfile - pointer to output file
144 */
145 g_init_bits = init_bits;
146 g_outfile = outfile;
147
148 /*
149 * Set up the necessary values
150 */
151 offset = 0;
152 out_count = 0;
153 clear_flg = 0;
154 in_count = 1;
155 maxcode = MAXCODE(n_bits = g_init_bits);
156
157 ClearCode = (1 << (init_bits - 1));
158 EOFCode = ClearCode + 1;
159 free_ent = ClearCode + 2;
160
161 char_init();
162
163 ent = ReadValue();
164
165 hshift = 0;
166 for ( fcode = (long) hsize; fcode < 65536L; fcode *= 2L )
167 hshift++;
168 hshift = 8 - hshift; /* set hash code range bound */
169
170 hsize_reg = hsize;
171 cl_hash( (count_int) hsize_reg); /* clear hash table */
172
173 output( (code_int)ClearCode );
174
175 #ifdef SIGNED_COMPARE_SLOW
176 while ( (c = ReadValue() ) != (unsigned) EOF ) {
177 #else
178 while ( (c = ReadValue()) != EOF ) {
179 #endif
180
181 in_count++;
182
183 fcode = (long) (((long) c << maxbits) + ent);
184 i = (((code_int)c << hshift) ^ ent); /* xor hashing */
185
186 if ( HashTabOf (i) == fcode ) {
187 ent = CodeTabOf (i);
188 continue;
189 } else if ( (long)HashTabOf (i) < 0 ) /* empty slot */
190 goto nomatch;
191 disp = hsize_reg - i; /* secondary hash (after G. Knott) */
192 if ( i == 0 )
193 disp = 1;
194 probe:
195 if ( (i -= disp) < 0 )
196 i += hsize_reg;
197
198 if ( HashTabOf (i) == fcode ) {
199 ent = CodeTabOf (i);
200 continue;
201 }
202 if ( (long)HashTabOf (i) > 0 )
203 goto probe;
204 nomatch:
205 output ( (code_int) ent );
206 out_count++;
207 ent = c;
208 #ifdef SIGNED_COMPARE_SLOW
209 if ( (unsigned) free_ent < (unsigned) maxmaxcode) {
210 #else
211 if ( free_ent < maxmaxcode ) {
212 #endif
213 CodeTabOf (i) = free_ent++; /* code -> hashtable */
214 HashTabOf (i) = fcode;
215 } else
216 cl_block();
217 }
218 /*
219 * Put out the final code.
220 */
221 output( (code_int)ent );
222 out_count++;
223 output( (code_int) EOFCode );
224
225 return;
226 }
227
228 /*****************************************************************
229 * TAG( output )
230 *
231 * Output the given code.
232 * Inputs:
233 * code: A n_bits-bit integer. If == -1, then EOF. This assumes
234 * that n_bits =< (long)wordsize - 1.
235 * Outputs:
236 * Outputs code to the file.
237 * Assumptions:
238 * Chars are 8 bits long.
239 * Algorithm:
240 * Maintain a GIFBITS character long buffer (so that 8 codes will
241 * fit in it exactly). Use the VAX insv instruction to insert each
242 * code in turn. When the buffer fills up empty it and start over.
243 */
244
245 static unsigned long cur_accum = 0;
246 static int cur_bits = 0;
247
248 static
249 unsigned long masks[] = { 0x0000, 0x0001, 0x0003, 0x0007, 0x000F,
250 0x001F, 0x003F, 0x007F, 0x00FF,
251 0x01FF, 0x03FF, 0x07FF, 0x0FFF,
252 0x1FFF, 0x3FFF, 0x7FFF, 0xFFFF };
253
254 static
output(code)255 output( code )
256 code_int code;
257 {
258 cur_accum &= masks[ cur_bits ];
259
260 if( cur_bits > 0 )
261 cur_accum |= ((long)code << cur_bits);
262 else
263 cur_accum = code;
264
265 cur_bits += n_bits;
266
267 while( cur_bits >= 8 ) {
268 char_out( (unsigned int)(cur_accum & 0xff) );
269 cur_accum >>= 8;
270 cur_bits -= 8;
271 }
272
273 /*
274 * If the next entry is going to be too big for the code size,
275 * then increase it, if possible.
276 */
277 if ( free_ent > maxcode || clear_flg ) {
278
279 if( clear_flg ) {
280
281 maxcode = MAXCODE (n_bits = g_init_bits);
282 clear_flg = 0;
283
284 } else {
285
286 n_bits++;
287 if ( n_bits == maxbits )
288 maxcode = maxmaxcode;
289 else
290 maxcode = MAXCODE(n_bits);
291 }
292 }
293
294 if( code == EOFCode ) {
295 /*
296 * At EOF, write the rest of the buffer.
297 */
298 while( cur_bits > 0 ) {
299 char_out( (unsigned int)(cur_accum & 0xff) );
300 cur_accum >>= 8;
301 cur_bits -= 8;
302 }
303
304 flush_char();
305
306 fflush( g_outfile );
307
308 if( ferror( g_outfile ) )
309 writeerr();
310 }
311 }
312
313 /*
314 * Clear out the hash table
315 */
316 static
cl_block()317 cl_block () /* table clear for block compress */
318 {
319
320 cl_hash ( (count_int) hsize );
321 free_ent = ClearCode + 2;
322 clear_flg = 1;
323
324 output( (code_int)ClearCode );
325 }
326
327 static
cl_hash(hsize)328 cl_hash(hsize) /* reset code table */
329 register count_int hsize;
330 {
331
332 register count_int *htab_p = htab+hsize;
333
334 register long i;
335 register long m1 = -1;
336
337 i = hsize - 16;
338 do { /* might use Sys V memset(3) here */
339 *(htab_p-16) = m1;
340 *(htab_p-15) = m1;
341 *(htab_p-14) = m1;
342 *(htab_p-13) = m1;
343 *(htab_p-12) = m1;
344 *(htab_p-11) = m1;
345 *(htab_p-10) = m1;
346 *(htab_p-9) = m1;
347 *(htab_p-8) = m1;
348 *(htab_p-7) = m1;
349 *(htab_p-6) = m1;
350 *(htab_p-5) = m1;
351 *(htab_p-4) = m1;
352 *(htab_p-3) = m1;
353 *(htab_p-2) = m1;
354 *(htab_p-1) = m1;
355 htab_p -= 16;
356 } while ((i -= 16) >= 0);
357
358 for ( i += 16; i > 0; i-- )
359 *--htab_p = m1;
360 }
361
362 static
writeerr()363 writeerr()
364 {
365 printf( "error writing output file\n" );
366 exit(1);
367 }
368
369 /******************************************************************************
370 *
371 * GIF Specific routines
372 *
373 ******************************************************************************/
374
375 /*
376 * Number of characters so far in this 'packet'
377 */
378 static int a_count;
379
380 /*
381 * Set up the 'byte output' routine
382 */
383 static
char_init()384 char_init()
385 {
386 a_count = 0;
387 cur_accum = 0;
388 cur_bits = 0;
389 }
390
391 /*
392 * Define the storage for the packet accumulator
393 */
394 static char accum[ 256 ];
395
396 /*
397 * Add a character to the end of the current packet, and if it is 254
398 * characters, flush the packet to disk.
399 */
400 static
char_out(c)401 char_out( c )
402 int c;
403 {
404 accum[ a_count++ ] = c;
405 if( a_count >= 254 )
406 flush_char();
407 }
408
409 /*
410 * Flush the packet to disk, and reset the accumulator
411 */
412 static
flush_char()413 flush_char()
414 {
415 if( a_count > 0 ) {
416 fputc( a_count, g_outfile );
417 fwrite( accum, 1, a_count, g_outfile );
418 a_count = 0;
419 }
420 }
421
422 /* The End */
423