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1/*
2 * $Source: /homes/cvs/ftape-stacked/ftape/compressor/lzrw3.c,v $
3 * $Revision: 1.1 $
4 * $Date: 1997/10/05 19:12:29 $
5 *
6 * Implementation of Ross Williams lzrw3 algorithm. Adaption for zftape.
7 *
8 */
9
10#include "../compressor/lzrw3.h" /* Defines single exported function "compress". */
11
12/******************************************************************************/
13/* */
14/* LZRW3.C */
15/* */
16/******************************************************************************/
17/* */
18/* Author : Ross Williams. */
19/* Date : 30-Jun-1991. */
20/* Release : 1. */
21/* */
22/******************************************************************************/
23/* */
24/* This file contains an implementation of the LZRW3 data compression */
25/* algorithm in C. */
26/* */
27/* The algorithm is a general purpose compression algorithm that runs fast */
28/* and gives reasonable compression. The algorithm is a member of the Lempel */
29/* Ziv family of algorithms and bases its compression on the presence in the */
30/* data of repeated substrings. */
31/* */
32/* This algorithm is unpatented and the code is public domain. As the */
33/* algorithm is based on the LZ77 class of algorithms, it is unlikely to be */
34/* the subject of a patent challenge. */
35/* */
36/* Unlike the LZRW1 and LZRW1-A algorithms, the LZRW3 algorithm is */
37/* deterministic and is guaranteed to yield the same compressed */
38/* representation for a given file each time it is run. */
39/* */
40/* The LZRW3 algorithm was originally designed and implemented */
41/* by Ross Williams on 31-Dec-1990. */
42/* */
43/* Here are the results of applying this code, compiled under THINK C 4.0 */
44/* and running on a Mac-SE (8MHz 68000), to the standard calgary corpus. */
45/* */
46/* +----------------------------------------------------------------+ */
47/* | DATA COMPRESSION TEST | */
48/* | ===================== | */
49/* | Time of run : Sun 30-Jun-1991 09:31PM | */
50/* | Timing accuracy : One part in 100 | */
51/* | Context length : 262144 bytes (= 256.0000K) | */
52/* | Test suite : Calgary Corpus Suite | */
53/* | Files in suite : 14 | */
54/* | Algorithm : LZRW3 | */
55/* | Note: All averages are calculated from the un-rounded values. | */
56/* +----------------------------------------------------------------+ */
57/* | File Name Length CxB ComLen %Remn Bits Com K/s Dec K/s | */
58/* | ---------- ------ --- ------ ----- ---- ------- ------- | */
59/* | rpus:Bib.D 111261 1 55033 49.5 3.96 19.46 32.27 | */
60/* | us:Book1.D 768771 3 467962 60.9 4.87 17.03 31.07 | */
61/* | us:Book2.D 610856 3 317102 51.9 4.15 19.39 34.15 | */
62/* | rpus:Geo.D 102400 1 82424 80.5 6.44 11.65 18.18 | */
63/* | pus:News.D 377109 2 205670 54.5 4.36 17.14 27.47 | */
64/* | pus:Obj1.D 21504 1 13027 60.6 4.85 13.40 18.95 | */
65/* | pus:Obj2.D 246814 1 116286 47.1 3.77 19.31 30.10 | */
66/* | s:Paper1.D 53161 1 27522 51.8 4.14 18.60 31.15 | */
67/* | s:Paper2.D 82199 1 45160 54.9 4.40 18.45 32.84 | */
68/* | rpus:Pic.D 513216 2 122388 23.8 1.91 35.29 51.05 | */
69/* | us:Progc.D 39611 1 19669 49.7 3.97 18.87 30.64 | */
70/* | us:Progl.D 71646 1 28247 39.4 3.15 24.34 40.66 | */
71/* | us:Progp.D 49379 1 19377 39.2 3.14 23.91 39.23 | */
72/* | us:Trans.D 93695 1 33481 35.7 2.86 25.48 40.37 | */
73/* +----------------------------------------------------------------+ */
74/* | Average 224401 1 110953 50.0 4.00 20.17 32.72 | */
75/* +----------------------------------------------------------------+ */
76/* */
77/******************************************************************************/
78
79/******************************************************************************/
80
81/* The following structure is returned by the "compress" function below when */
82/* the user asks the function to return identifying information. */
83/* The most important field in the record is the working memory field which */
84/* tells the calling program how much working memory should be passed to */
85/* "compress" when it is called to perform a compression or decompression. */
86/* LZRW3 uses the same amount of memory during compression and decompression. */
87/* For more information on this structure see "compress.h". */
88
89#define U(X) ((ULONG) X)
90#define SIZE_P_BYTE (U(sizeof(UBYTE *)))
91#define SIZE_WORD (U(sizeof(UWORD )))
92#define ALIGNMENT_FUDGE (U(16))
93#define MEM_REQ ( U(4096)*(SIZE_P_BYTE) + ALIGNMENT_FUDGE )
94
95static struct compress_identity identity =
96{
97 U(0x032DDEA8), /* Algorithm identification number. */
98 MEM_REQ, /* Working memory (bytes) required. */
99 "LZRW3", /* Name of algorithm. */
100 "1.0", /* Version number of algorithm. */
101 "31-Dec-1990", /* Date of algorithm. */
102 "Public Domain", /* Copyright notice. */
103 "Ross N. Williams", /* Author of algorithm. */
104 "Renaissance Software", /* Affiliation of author. */
105 "Public Domain" /* Vendor of algorithm. */
106};
107
108LOCAL void compress_compress (UBYTE *,UBYTE *,ULONG,UBYTE *, LONG *);
109LOCAL void compress_decompress(UBYTE *,UBYTE *,LONG, UBYTE *, ULONG *);
110
111/******************************************************************************/
112
113/* This function is the only function exported by this module. */
114/* Depending on its first parameter, the function can be requested to */
115/* compress a block of memory, decompress a block of memory, or to identify */
116/* itself. For more information, see the specification file "compress.h". */
117
118EXPORT void lzrw3_compress(
119 UWORD action, /* Action to be performed. */
120 UBYTE *wrk_mem, /* Address of working memory we can use.*/
121 UBYTE *src_adr, /* Address of input data. */
122 LONG src_len, /* Length of input data. */
123 UBYTE *dst_adr, /* Address to put output data. */
124 void *p_dst_len /* Address of longword for length of output data.*/
125)
126{
127 switch (action)
128 {
129 case COMPRESS_ACTION_IDENTITY:
130 *((struct compress_identity **)p_dst_len)= &identity;
131 break;
132 case COMPRESS_ACTION_COMPRESS:
133 compress_compress(wrk_mem,src_adr,src_len,dst_adr,(LONG *)p_dst_len);
134 break;
135 case COMPRESS_ACTION_DECOMPRESS:
136 compress_decompress(wrk_mem,src_adr,src_len,dst_adr,(LONG *)p_dst_len);
137 break;
138 }
139}
140
141/******************************************************************************/
142/* */
143/* BRIEF DESCRIPTION OF THE LZRW3 ALGORITHM */
144/* ======================================== */
145/* The LZRW3 algorithm is identical to the LZRW1-A algorithm except that */
146/* instead of transmitting history offsets, it transmits hash table indexes. */
147/* In order to decode the indexes, the decompressor must maintain an */
148/* identical hash table. Copy items are straightforward:when the decompressor */
149/* receives a copy item, it simply looks up the hash table to translate the */
150/* index into a pointer into the data already decompressed. To update the */
151/* hash table, it replaces the same table entry with a pointer to the start */
152/* of the newly decoded phrase. The tricky part is with literal items, for at */
153/* the time that the decompressor receives a literal item the decompressor */
154/* does not have the three bytes in the Ziv (that the compressor has) to */
155/* perform the three-byte hash. To solve this problem, in LZRW3, both the */
156/* compressor and decompressor are wired up so that they "buffer" these */
157/* literals and update their hash tables only when three bytes are available. */
158/* This makes the maximum buffering 2 bytes. */
159/* */
160/* Replacement of offsets by hash table indexes yields a few percent extra */
161/* compression at the cost of some speed. LZRW3 is slower than LZRW1, LZRW1-A */
162/* and LZRW2, but yields better compression. */
163/* */
164/* Extra compression could be obtained by using a hash table of depth two. */
165/* However, increasing the depth above one incurs a significant decrease in */
166/* compression speed which was not considered worthwhile. Another reason for */
167/* keeping the depth down to one was to allow easy comparison with the */
168/* LZRW1-A and LZRW2 algorithms so as to demonstrate the exact effect of the */
169/* use of direct hash indexes. */
170/* */
171/* +---+ */
172/* |___|4095 */
173/* |___| */
174/* +---------------------*_|<---+ /----+---\ */
175/* | |___| +---|Hash | */
176/* | |___| |Function| */
177/* | |___| \--------/ */
178/* | |___|0 ^ */
179/* | +---+ | */
180/* | Hash +-----+ */
181/* | Table | */
182/* | --- */
183/* v ^^^ */
184/* +-------------------------------------|----------------+ */
185/* |||||||||||||||||||||||||||||||||||||||||||||||||||||||| */
186/* +-------------------------------------|----------------+ */
187/* | |1......18| | */
188/* |<------- Lempel=History ------------>|<--Ziv-->| | */
189/* | (=bytes already processed) |<-Still to go-->| */
190/* |<-------------------- INPUT BLOCK ------------------->| */
191/* */
192/* The diagram above for LZRW3 looks almost identical to the diagram for */
193/* LZRW1. The difference is that in LZRW3, the compressor transmits hash */
194/* table indices instead of Lempel offsets. For this to work, the */
195/* decompressor must maintain a hash table as well as the compressor and both */
196/* compressor and decompressor must "buffer" literals, as the decompressor */
197/* cannot hash phrases commencing with a literal until another two bytes have */
198/* arrived. */
199/* */
200/* LZRW3 Algorithm Execution Summary */
201/* --------------------------------- */
202/* 1. Hash the first three bytes of the Ziv to yield a hash table index h. */
203/* 2. Look up the hash table yielding history pointer p. */
204/* 3. Match where p points with the Ziv. If there is a match of three or */
205/* more bytes, code those bytes (in the Ziv) as a copy item, otherwise */
206/* code the next byte in the Ziv as a literal item. */
207/* 4. Update the hash table as possible subject to the constraint that only */
208/* phrases commencing three bytes back from the Ziv can be hashed and */
209/* entered into the hash table. (This enables the decompressor to keep */
210/* pace). See the description and code for more details. */
211/* */
212/******************************************************************************/
213/* */
214/* DEFINITION OF COMPRESSED FILE FORMAT */
215/* ==================================== */
216/* * A compressed file consists of a COPY FLAG followed by a REMAINDER. */
217/* * The copy flag CF uses up four bytes with the first byte being the */
218/* least significant. */
219/* * If CF=1, then the compressed file represents the remainder of the file */
220/* exactly. Otherwise CF=0 and the remainder of the file consists of zero */
221/* or more GROUPS, each of which represents one or more bytes. */
222/* * Each group consists of two bytes of CONTROL information followed by */
223/* sixteen ITEMs except for the last group which can contain from one */
224/* to sixteen items. */
225/* * An item can be either a LITERAL item or a COPY item. */
226/* * Each item corresponds to a bit in the control bytes. */
227/* * The first control byte corresponds to the first 8 items in the group */
228/* with bit 0 corresponding to the first item in the group and bit 7 to */
229/* the eighth item in the group. */
230/* * The second control byte corresponds to the second 8 items in the group */
231/* with bit 0 corresponding to the ninth item in the group and bit 7 to */
232/* the sixteenth item in the group. */
233/* * A zero bit in a control word means that the corresponding item is a */
234/* literal item. A one bit corresponds to a copy item. */
235/* * A literal item consists of a single byte which represents itself. */
236/* * A copy item consists of two bytes that represent from 3 to 18 bytes. */
237/* * The first byte in a copy item will be denoted C1. */
238/* * The second byte in a copy item will be denoted C2. */
239/* * Bits will be selected using square brackets. */
240/* For example: C1[0..3] is the low nibble of the first control byte. */
241/* of copy item C1. */
242/* * The LENGTH of a copy item is defined to be C1[0..3]+3 which is a number */
243/* in the range [3,18]. */
244/* * The INDEX of a copy item is defined to be C1[4..7]*256+C2[0..8] which */
245/* is a number in the range [0,4095]. */
246/* * A copy item represents the sequence of bytes */
247/* text[POS-OFFSET..POS-OFFSET+LENGTH-1] where */
248/* text is the entire text of the uncompressed string. */
249/* POS is the index in the text of the character following the */
250/* string represented by all the items preceeding the item */
251/* being defined. */
252/* OFFSET is obtained from INDEX by looking up the hash table. */
253/* */
254/******************************************************************************/
255
256/* The following #define defines the length of the copy flag that appears at */
257/* the start of the compressed file. The value of four bytes was chosen */
258/* because the fast_copy routine on my Macintosh runs faster if the source */
259/* and destination blocks are relatively longword aligned. */
260/* The actual flag data appears in the first byte. The rest are zeroed so as */
261/* to normalize the compressed representation (i.e. not non-deterministic). */
262#define FLAG_BYTES 4
263
264/* The following #defines define the meaning of the values of the copy */
265/* flag at the start of the compressed file. */
266#define FLAG_COMPRESS 0 /* Signals that output was result of compression. */
267#define FLAG_COPY 1 /* Signals that output was simply copied over. */
268
269/* The 68000 microprocessor (on which this algorithm was originally developed */
270/* is fussy about non-aligned arrays of words. To avoid these problems the */
271/* following macro can be used to "waste" from 0 to 3 bytes so as to align */
272/* the argument pointer. */
273#define ULONG_ALIGN_UP(X) ((((ULONG)X)+sizeof(ULONG)-1)&~(sizeof(ULONG)-1))
274
275
276/* The following constant defines the maximum length of an uncompressed item. */
277/* This definition must not be changed; its value is hardwired into the code. */
278/* The longest number of bytes that can be spanned by a single item is 18 */
279/* for the longest copy item. */
280#define MAX_RAW_ITEM (18)
281
282/* The following constant defines the maximum length of an uncompressed group.*/
283/* This definition must not be changed; its value is hardwired into the code. */
284/* A group contains at most 16 items which explains this definition. */
285#define MAX_RAW_GROUP (16*MAX_RAW_ITEM)
286
287/* The following constant defines the maximum length of a compressed group. */
288/* This definition must not be changed; its value is hardwired into the code. */
289/* A compressed group consists of two control bytes followed by up to 16 */
290/* compressed items each of which can have a maximum length of two bytes. */
291#define MAX_CMP_GROUP (2+16*2)
292
293/* The following constant defines the number of entries in the hash table. */
294/* This definition must not be changed; its value is hardwired into the code. */
295#define HASH_TABLE_LENGTH (4096)
296
297/* LZRW3, unlike LZRW1(-A), must initialize its hash table so as to enable */
298/* the compressor and decompressor to stay in step maintaining identical hash */
299/* tables. In an early version of the algorithm, the tables were simply */
300/* initialized to zero and a check for zero was included just before the */
301/* matching code. However, this test costs time. A better solution is to */
302/* initialize all the entries in the hash table to point to a constant */
303/* string. The decompressor does the same. This solution requires no extra */
304/* test. The contents of the string do not matter so long as the string is */
305/* the same for the compressor and decompressor and contains at least */
306/* MAX_RAW_ITEM bytes. I chose consecutive decimal digits because they do not */
307/* have white space problems (e.g. there is no chance that the compiler will */
308/* replace more than one space by a TAB) and because they make the length of */
309/* the string obvious by inspection. */
310#define START_STRING_18 ((UBYTE *) "123456789012345678")
311
312/* In this algorithm, hash values have to be calculated at more than one */
313/* point. The following macro neatens the code up for this. */
314#define HASH(PTR) \
315 (((40543*(((*(PTR))<<8)^((*((PTR)+1))<<4)^(*((PTR)+2))))>>4) & 0xFFF)
316
317/******************************************************************************/
318
319/* Input : Hand over the required amount of working memory in p_wrk_mem. */
320/* Input : Specify input block using p_src_first and src_len. */
321/* Input : Point p_dst_first to the start of the output zone (OZ). */
322/* Input : Point p_dst_len to a ULONG to receive the output length. */
323/* Input : Input block and output zone must not overlap. */
324/* Output : Length of output block written to *p_dst_len. */
325/* Output : Output block in Mem[p_dst_first..p_dst_first+*p_dst_len-1]. May */
326/* Output : write in OZ=Mem[p_dst_first..p_dst_first+src_len+MAX_CMP_GROUP-1].*/
327/* Output : Upon completion guaranteed *p_dst_len<=src_len+FLAG_BYTES. */
328LOCAL void compress_compress(UBYTE *p_wrk_mem,
329 UBYTE *p_src_first, ULONG src_len,
330 UBYTE *p_dst_first, LONG *p_dst_len)
331{
332 /* p_src and p_dst step through the source and destination blocks. */
333 register UBYTE *p_src = p_src_first;
334 register UBYTE *p_dst = p_dst_first;
335
336 /* The following variables are never modified and are used in the */
337 /* calculations that determine when the main loop terminates. */
338 UBYTE *p_src_post = p_src_first+src_len;
339 UBYTE *p_dst_post = p_dst_first+src_len;
340 UBYTE *p_src_max1 = p_src_first+src_len-MAX_RAW_ITEM;
341 UBYTE *p_src_max16 = p_src_first+src_len-MAX_RAW_ITEM*16;
342
343 /* The variables 'p_control' and 'control' are used to buffer control bits. */
344 /* Before each group is processed, the next two bytes of the output block */
345 /* are set aside for the control word for the group about to be processed. */
346 /* 'p_control' is set to point to the first byte of that word. Meanwhile, */
347 /* 'control' buffers the control bits being generated during the processing */
348 /* of the group. Instead of having a counter to keep track of how many items */
349 /* have been processed (=the number of bits in the control word), at the */
350 /* start of each group, the top word of 'control' is filled with 1 bits. */
351 /* As 'control' is shifted for each item, the 1 bits in the top word are */
352 /* absorbed or destroyed. When they all run out (i.e. when the top word is */
353 /* all zero bits, we know that we are at the end of a group. */
354# define TOPWORD 0xFFFF0000
355 UBYTE *p_control;
356 register ULONG control=TOPWORD;
357
358 /* THe variable 'hash' always points to the first element of the hash table. */
359 UBYTE **hash= (UBYTE **) ULONG_ALIGN_UP(p_wrk_mem);
360
361 /* The following two variables represent the literal buffer. p_h1 points to */
362 /* the hash table entry corresponding to the youngest literal. p_h2 points */
363 /* to the hash table entry corresponding to the second youngest literal. */
364 /* Note: p_h1=0=>p_h2=0 because zero values denote absence of a pending */
365 /* literal. The variables are initialized to zero meaning an empty "buffer". */
366 UBYTE **p_h1=NULL;
367 UBYTE **p_h2=NULL;
368
369 /* To start, we write the flag bytes. Being optimistic, we set the flag to */
370 /* FLAG_COMPRESS. The remaining flag bytes are zeroed so as to keep the */
371 /* algorithm deterministic. */
372 *p_dst++=FLAG_COMPRESS;
373 {UWORD i; for (i=2;i<=FLAG_BYTES;i++) *p_dst++=0;}
374
375 /* Reserve the first word of output as the control word for the first group. */
376 /* Note: This is undone at the end if the input block is empty. */
377 p_control=p_dst; p_dst+=2;
378
379 /* Initialize all elements of the hash table to point to a constant string. */
380 /* Use of an unrolled loop speeds this up considerably. */
381 {UWORD i; UBYTE **p_h=hash;
382# define ZH *p_h++=START_STRING_18
383 for (i=0;i<256;i++) /* 256=HASH_TABLE_LENGTH/16. */
384 {ZH;ZH;ZH;ZH;
385 ZH;ZH;ZH;ZH;
386 ZH;ZH;ZH;ZH;
387 ZH;ZH;ZH;ZH;}
388 }
389
390 /* The main loop processes either 1 or 16 items per iteration. As its */
391 /* termination logic is complicated, I have opted for an infinite loop */
392 /* structure containing 'break' and 'goto' statements. */
393 while (TRUE)
394 {/* Begin main processing loop. */
395
396 /* Note: All the variables here except unroll should be defined within */
397 /* the inner loop. Unfortunately the loop hasn't got a block. */
398 register UBYTE *p; /* Scans through targ phrase during matching. */
399 register UBYTE *p_ziv= NULL ; /* Points to first byte of current Ziv. */
400 register UWORD unroll; /* Loop counter for unrolled inner loop. */
401 register UWORD index; /* Index of current hash table entry. */
402 register UBYTE **p_h0 = NULL ; /* Pointer to current hash table entry. */
403
404 /* Test for overrun and jump to overrun code if necessary. */
405 if (p_dst>p_dst_post)
406 goto overrun;
407
408 /* The following cascade of if statements efficiently catches and deals */
409 /* with varying degrees of closeness to the end of the input block. */
410 /* When we get very close to the end, we stop updating the table and */
411 /* code the remaining bytes as literals. This makes the code simpler. */
412 unroll=16;
413 if (p_src>p_src_max16)
414 {
415 unroll=1;
416 if (p_src>p_src_max1)
417 {
418 if (p_src==p_src_post)
419 break;
420 else
421 goto literal;
422 }
423 }
424
425 /* This inner unrolled loop processes 'unroll' (whose value is either 1 */
426 /* or 16) items. I have chosen to implement this loop with labels and */
427 /* gotos to heighten the ease with which the loop may be implemented with */
428 /* a single decrement and branch instruction in assembly language and */
429 /* also because the labels act as highly readable place markers. */
430 /* (Also because we jump into the loop for endgame literals (see above)). */
431
432 begin_unrolled_loop:
433
434 /* To process the next phrase, we hash the next three bytes and use */
435 /* the resultant hash table index to look up the hash table. A pointer */
436 /* to the entry is stored in p_h0 so as to avoid an array lookup. The */
437 /* hash table entry *p_h0 is looked up yielding a pointer p to a */
438 /* potential match of the Ziv in the history. */
439 index=HASH(p_src);
440 p_h0=&hash[index];
441 p=*p_h0;
442
443 /* Having looked up the candidate position, we are in a position to */
444 /* attempt a match. The match loop has been unrolled using the PS */
445 /* macro so that failure within the first three bytes automatically */
446 /* results in the literal branch being taken. The coding is simple. */
447 /* p_ziv saves p_src so we can let p_src wander. */
448# define PS *p++!=*p_src++
449 p_ziv=p_src;
450 if (PS || PS || PS)
451 {
452 /* Literal. */
453
454 /* Code the literal byte as itself and a zero control bit. */
455 p_src=p_ziv; literal: *p_dst++=*p_src++; control&=0xFFFEFFFF;
456
457 /* We have just coded a literal. If we had two pending ones, that */
458 /* makes three and we can update the hash table. */
459 if (p_h2!=0)
460 {*p_h2=p_ziv-2;}
461
462 /* In any case, rotate the hash table pointers for next time. */
463 p_h2=p_h1; p_h1=p_h0;
464
465 }
466 else
467 {
468 /* Copy */
469
470 /* Match up to 15 remaining bytes using an unrolled loop and code. */
471#if 0
472 PS || PS || PS || PS || PS || PS || PS || PS ||
473 PS || PS || PS || PS || PS || PS || PS || p_src++;
474#else
475 if (
476 !( PS || PS || PS || PS || PS || PS || PS || PS ||
477 PS || PS || PS || PS || PS || PS || PS )
478 ) p_src++;
479#endif
480 *p_dst++=((index&0xF00)>>4)|(--p_src-p_ziv-3);
481 *p_dst++=index&0xFF;
482
483 /* As we have just coded three bytes, we are now in a position to */
484 /* update the hash table with the literal bytes that were pending */
485 /* upon the arrival of extra context bytes. */
486 if (p_h1!=0)
487 {
488 if (p_h2)
489 {*p_h2=p_ziv-2; p_h2=NULL;}
490 *p_h1=p_ziv-1; p_h1=NULL;
491 }
492
493 /* In any case, we can update the hash table based on the current */
494 /* position as we just coded at least three bytes in a copy items. */
495 *p_h0=p_ziv;
496
497 }
498 control>>=1;
499
500 /* This loop is all set up for a decrement and jump instruction! */
501#ifndef linux
502` end_unrolled_loop: if (--unroll) goto begin_unrolled_loop;
503#else
504 /* end_unrolled_loop: */ if (--unroll) goto begin_unrolled_loop;
505#endif
506
507 /* At this point it will nearly always be the end of a group in which */
508 /* case, we have to do some control-word processing. However, near the */
509 /* end of the input block, the inner unrolled loop is only executed once. */
510 /* This necessitates the 'if' test. */
511 if ((control&TOPWORD)==0)
512 {
513 /* Write the control word to the place we saved for it in the output. */
514 *p_control++= control &0xFF;
515 *p_control = (control>>8) &0xFF;
516
517 /* Reserve the next word in the output block for the control word */
518 /* for the group about to be processed. */
519 p_control=p_dst; p_dst+=2;
520
521 /* Reset the control bits buffer. */
522 control=TOPWORD;
523 }
524
525 } /* End main processing loop. */
526
527 /* After the main processing loop has executed, all the input bytes have */
528 /* been processed. However, the control word has still to be written to the */
529 /* word reserved for it in the output at the start of the most recent group. */
530 /* Before writing, the control word has to be shifted so that all the bits */
531 /* are in the right place. The "empty" bit positions are filled with 1s */
532 /* which partially fill the top word. */
533 while(control&TOPWORD) control>>=1;
534 *p_control++= control &0xFF;
535 *p_control++=(control>>8) &0xFF;
536
537 /* If the last group contained no items, delete the control word too. */
538 if (p_control==p_dst) p_dst-=2;
539
540 /* Write the length of the output block to the dst_len parameter and return. */
541 *p_dst_len=p_dst-p_dst_first;
542 return;
543
544 /* Jump here as soon as an overrun is detected. An overrun is defined to */
545 /* have occurred if p_dst>p_dst_first+src_len. That is, the moment the */
546 /* length of the output written so far exceeds the length of the input block.*/
547 /* The algorithm checks for overruns at least at the end of each group */
548 /* which means that the maximum overrun is MAX_CMP_GROUP bytes. */
549 /* Once an overrun occurs, the only thing to do is to set the copy flag and */
550 /* copy the input over. */
551 overrun:
552#if 0
553 *p_dst_first=FLAG_COPY;
554 fast_copy(p_src_first,p_dst_first+FLAG_BYTES,src_len);
555 *p_dst_len=src_len+FLAG_BYTES;
556#else
557 fast_copy(p_src_first,p_dst_first,src_len);
558 *p_dst_len= -src_len; /* return a negative number to indicate uncompressed data */
559#endif
560}
561
562/******************************************************************************/
563
564/* Input : Hand over the required amount of working memory in p_wrk_mem. */
565/* Input : Specify input block using p_src_first and src_len. */
566/* Input : Point p_dst_first to the start of the output zone. */
567/* Input : Point p_dst_len to a ULONG to receive the output length. */
568/* Input : Input block and output zone must not overlap. User knows */
569/* Input : upperbound on output block length from earlier compression. */
570/* Input : In any case, maximum expansion possible is nine times. */
571/* Output : Length of output block written to *p_dst_len. */
572/* Output : Output block in Mem[p_dst_first..p_dst_first+*p_dst_len-1]. */
573/* Output : Writes only in Mem[p_dst_first..p_dst_first+*p_dst_len-1]. */
574LOCAL void compress_decompress( UBYTE *p_wrk_mem,
575 UBYTE *p_src_first, LONG src_len,
576 UBYTE *p_dst_first, ULONG *p_dst_len)
577{
578 /* Byte pointers p_src and p_dst scan through the input and output blocks. */
579 register UBYTE *p_src = p_src_first+FLAG_BYTES;
580 register UBYTE *p_dst = p_dst_first;
581 /* we need to avoid a SEGV when trying to uncompress corrupt data */
582 register UBYTE *p_dst_post = p_dst_first + *p_dst_len;
583
584 /* The following two variables are never modified and are used to control */
585 /* the main loop. */
586 UBYTE *p_src_post = p_src_first+src_len;
587 UBYTE *p_src_max16 = p_src_first+src_len-(MAX_CMP_GROUP-2);
588
589 /* The hash table is the only resident of the working memory. The hash table */
590 /* contains HASH_TABLE_LENGTH=4096 pointers to positions in the history. To */
591 /* keep Macintoshes happy, it is longword aligned. */
592 UBYTE **hash = (UBYTE **) ULONG_ALIGN_UP(p_wrk_mem);
593
594 /* The variable 'control' is used to buffer the control bits which appear in */
595 /* groups of 16 bits (control words) at the start of each compressed group. */
596 /* When each group is read, bit 16 of the register is set to one. Whenever */
597 /* a new bit is needed, the register is shifted right. When the value of the */
598 /* register becomes 1, we know that we have reached the end of a group. */
599 /* Initializing the register to 1 thus instructs the code to follow that it */
600 /* should read a new control word immediately. */
601 register ULONG control=1;
602
603 /* The value of 'literals' is always in the range 0..3. It is the number of */
604 /* consecutive literal items just seen. We have to record this number so as */
605 /* to know when to update the hash table. When literals gets to 3, there */
606 /* have been three consecutive literals and we can update at the position of */
607 /* the oldest of the three. */
608 register UWORD literals=0;
609
610 /* Check the leading copy flag to see if the compressor chose to use a copy */
611 /* operation instead of a compression operation. If a copy operation was */
612 /* used, then all we need to do is copy the data over, set the output length */
613 /* and return. */
614#if 0
615 if (*p_src_first==FLAG_COPY)
616 {
617 fast_copy(p_src_first+FLAG_BYTES,p_dst_first,src_len-FLAG_BYTES);
618 *p_dst_len=src_len-FLAG_BYTES;
619 return;
620 }
621#else
622 if ( src_len < 0 )
623 {
624 fast_copy(p_src_first,p_dst_first,-src_len );
625 *p_dst_len = (ULONG)-src_len;
626 return;
627 }
628#endif
629
630 /* Initialize all elements of the hash table to point to a constant string. */
631 /* Use of an unrolled loop speeds this up considerably. */
632 {UWORD i; UBYTE **p_h=hash;
633# define ZJ *p_h++=START_STRING_18
634 for (i=0;i<256;i++) /* 256=HASH_TABLE_LENGTH/16. */
635 {ZJ;ZJ;ZJ;ZJ;
636 ZJ;ZJ;ZJ;ZJ;
637 ZJ;ZJ;ZJ;ZJ;
638 ZJ;ZJ;ZJ;ZJ;}
639 }
640
641 /* The outer loop processes either 1 or 16 items per iteration depending on */
642 /* how close p_src is to the end of the input block. */
643 while (p_src!=p_src_post)
644 {/* Start of outer loop */
645
646 register UWORD unroll; /* Counts unrolled loop executions. */
647
648 /* When 'control' has the value 1, it means that the 16 buffered control */
649 /* bits that were read in at the start of the current group have all been */
650 /* shifted out and that all that is left is the 1 bit that was injected */
651 /* into bit 16 at the start of the current group. When we reach the end */
652 /* of a group, we have to load a new control word and inject a new 1 bit. */
653 if (control==1)
654 {
655 control=0x10000|*p_src++;
656 control|=(*p_src++)<<8;
657 }
658
659 /* If it is possible that we are within 16 groups from the end of the */
660 /* input, execute the unrolled loop only once, else process a whole group */
661 /* of 16 items by looping 16 times. */
662 unroll= p_src<=p_src_max16 ? 16 : 1;
663
664 /* This inner loop processes one phrase (item) per iteration. */
665 while (unroll--)
666 { /* Begin unrolled inner loop. */
667
668 /* Process a literal or copy item depending on the next control bit. */
669 if (control&1)
670 {
671 /* Copy item. */
672
673 register UBYTE *p; /* Points to place from which to copy. */
674 register UWORD lenmt; /* Length of copy item minus three. */
675 register UBYTE **p_hte; /* Pointer to current hash table entry.*/
676 register UBYTE *p_ziv=p_dst; /* Pointer to start of current Ziv. */
677
678 /* Read and dismantle the copy word. Work out from where to copy. */
679 lenmt=*p_src++;
680 p_hte=&hash[((lenmt&0xF0)<<4)|*p_src++];
681 p=*p_hte;
682 lenmt&=0xF;
683
684 /* Now perform the copy using a half unrolled loop. */
685 *p_dst++=*p++;
686 *p_dst++=*p++;
687 *p_dst++=*p++;
688 while (lenmt--)
689 *p_dst++=*p++;
690
691 /* Because we have just received 3 or more bytes in a copy item */
692 /* (whose bytes we have just installed in the output), we are now */
693 /* in a position to flush all the pending literal hashings that had */
694 /* been postponed for lack of bytes. */
695 if (literals>0)
696 {
697 register UBYTE *r=p_ziv-literals;
698 hash[HASH(r)]=r;
699 if (literals==2)
700 {r++; hash[HASH(r)]=r;}
701 literals=0;
702 }
703
704 /* In any case, we can immediately update the hash table with the */
705 /* current position. We don't need to do a HASH(...) to work out */
706 /* where to put the pointer, as the compressor just told us!!! */
707 *p_hte=p_ziv;
708
709 }
710 else
711 {
712 /* Literal item. */
713
714 /* Copy over the literal byte. */
715 *p_dst++=*p_src++;
716
717 /* If we now have three literals waiting to be hashed into the hash */
718 /* table, we can do one of them now (because there are three). */
719 if (++literals == 3)
720 {register UBYTE *p=p_dst-3; hash[HASH(p)]=p; literals=2;}
721 }
722
723 /* Shift the control buffer so the next control bit is in bit 0. */
724 control>>=1;
725#if 1
726 if (p_dst > p_dst_post)
727 {
728 /* Shit: we tried to decompress corrupt data */
729 *p_dst_len = 0;
730 return;
731 }
732#endif
733 } /* End unrolled inner loop. */
734
735 } /* End of outer loop */
736
737 /* Write the length of the decompressed data before returning. */
738 *p_dst_len=p_dst-p_dst_first;
739}
740
741/******************************************************************************/
742/* End of LZRW3.C */
743/******************************************************************************/
generated by cgit v1.2.2 (git 2.25.0) at 2025-01-01 19:52:16 -0500