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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 377 378 379 380 381 382 383 384 385 386 387 388 389 390 391 392 393 394 395 396 397 398 399 400 401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417 418 419 420 421 422 423 424 425 426 427 428 429 430 431 432 433 434 435 436 437 438 439 440 441 442 443 444 445 446 447 448 449 450 451 452 453 454 455 456 457 458 459 460 461 462 463 464 465 466 467 468 469 470 471 472 473 474 475 476 477 478 479 480 481 482 483 484 485 486 487 488 489 490 491 492 493 494 495 496 497 498 499 500 501 502 503 504 505 506 507 508 509 510 511 512 513 514 515 516 517 518 519 520 521 522 523 524 525 526 527 528 529 530 531 532 533 534 535 536 537 538 539 540 541 542 543 544 545 546 547 548 549 550 551 552 553 554 555 556 557 558 559 560 561 562 563 564 565 566 567 568 569 570 571 572 573 574 575 576 577 578 579 580 581 582 583 584 585 586 587 588 589 590 591 592 593 594 595 596 597 598 599 600 601 602 603 604 605 606 607 608 609 610 611 612 613 614 615 616 617 618 619 620 621 622 623 624 625 626 627 628 629 630 631 632 633 634 635 636 637 638 639 640 641 642 643 644 645 646 647 648 649 650 651 652 653 654 655 656 657 658 659 660 661 662 663 664 665 666 667 668 669 670 671 672 673 674 675 676 677 678 679 680 681 682 683 684 685 686 687 688 689 690 691 692 693 694 695 696 697 698 699 700 701 702 703 704 705 706 707 708 709 710 711 712 713 714 715 716 717 718 719 720 721 722 723 724 725 726 727 728 729 730 731 732 733 734 735 736 737 738 739 740 741 742 743 744 745 746 747 748 749 750 | /* * $Source: /homes/cvs/ftape-stacked/ftape/compressor/lzrw3.c,v $ * $Revision: 1.1 $ * $Date: 1997/10/05 19:12:29 $ * * Implementation of Ross Williams lzrw3 algorithm. Adaption for zftape. * */ #include "../compressor/lzrw3.h" /* Defines single exported function "compress". */ /******************************************************************************/ /* */ /* LZRW3.C */ /* */ /******************************************************************************/ /* */ /* Author : Ross Williams. */ /* Date : 30-Jun-1991. */ /* Release : 1. */ /* */ /******************************************************************************/ /* */ /* This file contains an implementation of the LZRW3 data compression */ /* algorithm in C. */ /* */ /* The algorithm is a general purpose compression algorithm that runs fast */ /* and gives reasonable compression. The algorithm is a member of the Lempel */ /* Ziv family of algorithms and bases its compression on the presence in the */ /* data of repeated substrings. */ /* */ /* This algorithm is unpatented and the code is public domain. As the */ /* algorithm is based on the LZ77 class of algorithms, it is unlikely to be */ /* the subject of a patent challenge. */ /* */ /* Unlike the LZRW1 and LZRW1-A algorithms, the LZRW3 algorithm is */ /* deterministic and is guaranteed to yield the same compressed */ /* representation for a given file each time it is run. */ /* */ /* The LZRW3 algorithm was originally designed and implemented */ /* by Ross Williams on 31-Dec-1990. */ /* */ /* Here are the results of applying this code, compiled under THINK C 4.0 */ /* and running on a Mac-SE (8MHz 68000), to the standard calgary corpus. */ /* */ /* +----------------------------------------------------------------+ */ /* | DATA COMPRESSION TEST | */ /* | ===================== | */ /* | Time of run : Sun 30-Jun-1991 09:31PM | */ /* | Timing accuracy : One part in 100 | */ /* | Context length : 262144 bytes (= 256.0000K) | */ /* | Test suite : Calgary Corpus Suite | */ /* | Files in suite : 14 | */ /* | Algorithm : LZRW3 | */ /* | Note: All averages are calculated from the un-rounded values. | */ /* +----------------------------------------------------------------+ */ /* | File Name Length CxB ComLen %Remn Bits Com K/s Dec K/s | */ /* | ---------- ------ --- ------ ----- ---- ------- ------- | */ /* | rpus:Bib.D 111261 1 55033 49.5 3.96 19.46 32.27 | */ /* | us:Book1.D 768771 3 467962 60.9 4.87 17.03 31.07 | */ /* | us:Book2.D 610856 3 317102 51.9 4.15 19.39 34.15 | */ /* | rpus:Geo.D 102400 1 82424 80.5 6.44 11.65 18.18 | */ /* | pus:News.D 377109 2 205670 54.5 4.36 17.14 27.47 | */ /* | pus:Obj1.D 21504 1 13027 60.6 4.85 13.40 18.95 | */ /* | pus:Obj2.D 246814 1 116286 47.1 3.77 19.31 30.10 | */ /* | s:Paper1.D 53161 1 27522 51.8 4.14 18.60 31.15 | */ /* | s:Paper2.D 82199 1 45160 54.9 4.40 18.45 32.84 | */ /* | rpus:Pic.D 513216 2 122388 23.8 1.91 35.29 51.05 | */ /* | us:Progc.D 39611 1 19669 49.7 3.97 18.87 30.64 | */ /* | us:Progl.D 71646 1 28247 39.4 3.15 24.34 40.66 | */ /* | us:Progp.D 49379 1 19377 39.2 3.14 23.91 39.23 | */ /* | us:Trans.D 93695 1 33481 35.7 2.86 25.48 40.37 | */ /* +----------------------------------------------------------------+ */ /* | Average 224401 1 110953 50.0 4.00 20.17 32.72 | */ /* +----------------------------------------------------------------+ */ /* */ /******************************************************************************/ /******************************************************************************/ /* The following structure is returned by the "compress" function below when */ /* the user asks the function to return identifying information. */ /* The most important field in the record is the working memory field which */ /* tells the calling program how much working memory should be passed to */ /* "compress" when it is called to perform a compression or decompression. */ /* LZRW3 uses the same amount of memory during compression and decompression. */ /* For more information on this structure see "compress.h". */ #define U(X) ((ULONG) X) #define SIZE_P_BYTE (U(sizeof(UBYTE *))) #define SIZE_WORD (U(sizeof(UWORD ))) #define ALIGNMENT_FUDGE (U(16)) #define MEM_REQ ( U(4096)*(SIZE_P_BYTE) + ALIGNMENT_FUDGE ) static struct compress_identity identity = { U(0x032DDEA8), /* Algorithm identification number. */ MEM_REQ, /* Working memory (bytes) required. */ "LZRW3", /* Name of algorithm. */ "1.0", /* Version number of algorithm. */ "31-Dec-1990", /* Date of algorithm. */ "Public Domain", /* Copyright notice. */ "Ross N. Williams", /* Author of algorithm. */ "Renaissance Software", /* Affiliation of author. */ "Public Domain" /* Vendor of algorithm. */ }; LOCAL void compress_compress (UBYTE *,UBYTE *,ULONG,UBYTE *, LONG *); LOCAL void compress_decompress(UBYTE *,UBYTE *,LONG, UBYTE *, ULONG *); /******************************************************************************/ /* This function is the only function exported by this module. */ /* Depending on its first parameter, the function can be requested to */ /* compress a block of memory, decompress a block of memory, or to identify */ /* itself. For more information, see the specification file "compress.h". */ EXPORT void lzrw3_compress(action,wrk_mem,src_adr,src_len,dst_adr,p_dst_len) UWORD action; /* Action to be performed. */ UBYTE *wrk_mem; /* Address of working memory we can use. */ UBYTE *src_adr; /* Address of input data. */ LONG src_len; /* Length of input data. */ UBYTE *dst_adr; /* Address to put output data. */ void *p_dst_len; /* Address of longword for length of output data. */ { switch (action) { case COMPRESS_ACTION_IDENTITY: *((struct compress_identity **)p_dst_len)= &identity; break; case COMPRESS_ACTION_COMPRESS: compress_compress(wrk_mem,src_adr,src_len,dst_adr,(LONG *)p_dst_len); break; case COMPRESS_ACTION_DECOMPRESS: compress_decompress(wrk_mem,src_adr,src_len,dst_adr,(LONG *)p_dst_len); break; } } /******************************************************************************/ /* */ /* BRIEF DESCRIPTION OF THE LZRW3 ALGORITHM */ /* ======================================== */ /* The LZRW3 algorithm is identical to the LZRW1-A algorithm except that */ /* instead of transmitting history offsets, it transmits hash table indexes. */ /* In order to decode the indexes, the decompressor must maintain an */ /* identical hash table. Copy items are straightforward:when the decompressor */ /* receives a copy item, it simply looks up the hash table to translate the */ /* index into a pointer into the data already decompressed. To update the */ /* hash table, it replaces the same table entry with a pointer to the start */ /* of the newly decoded phrase. The tricky part is with literal items, for at */ /* the time that the decompressor receives a literal item the decompressor */ /* does not have the three bytes in the Ziv (that the compressor has) to */ /* perform the three-byte hash. To solve this problem, in LZRW3, both the */ /* compressor and decompressor are wired up so that they "buffer" these */ /* literals and update their hash tables only when three bytes are available. */ /* This makes the maximum buffering 2 bytes. */ /* */ /* Replacement of offsets by hash table indexes yields a few percent extra */ /* compression at the cost of some speed. LZRW3 is slower than LZRW1, LZRW1-A */ /* and LZRW2, but yields better compression. */ /* */ /* Extra compression could be obtained by using a hash table of depth two. */ /* However, increasing the depth above one incurs a significant decrease in */ /* compression speed which was not considered worthwhile. Another reason for */ /* keeping the depth down to one was to allow easy comparison with the */ /* LZRW1-A and LZRW2 algorithms so as to demonstrate the exact effect of the */ /* use of direct hash indexes. */ /* */ /* +---+ */ /* |___|4095 */ /* |___| */ /* +---------------------*_|<---+ /----+---\ */ /* | |___| +---|Hash | */ /* | |___| |Function| */ /* | |___| \--------/ */ /* | |___|0 ^ */ /* | +---+ | */ /* | Hash +-----+ */ /* | Table | */ /* | --- */ /* v ^^^ */ /* +-------------------------------------|----------------+ */ /* |||||||||||||||||||||||||||||||||||||||||||||||||||||||| */ /* +-------------------------------------|----------------+ */ /* | |1......18| | */ /* |<------- Lempel=History ------------>|<--Ziv-->| | */ /* | (=bytes already processed) |<-Still to go-->| */ /* |<-------------------- INPUT BLOCK ------------------->| */ /* */ /* The diagram above for LZRW3 looks almost identical to the diagram for */ /* LZRW1. The difference is that in LZRW3, the compressor transmits hash */ /* table indices instead of Lempel offsets. For this to work, the */ /* decompressor must maintain a hash table as well as the compressor and both */ /* compressor and decompressor must "buffer" literals, as the decompressor */ /* cannot hash phrases commencing with a literal until another two bytes have */ /* arrived. */ /* */ /* LZRW3 Algorithm Execution Summary */ /* --------------------------------- */ /* 1. Hash the first three bytes of the Ziv to yield a hash table index h. */ /* 2. Look up the hash table yielding history pointer p. */ /* 3. Match where p points with the Ziv. If there is a match of three or */ /* more bytes, code those bytes (in the Ziv) as a copy item, otherwise */ /* code the next byte in the Ziv as a literal item. */ /* 4. Update the hash table as possible subject to the constraint that only */ /* phrases commencing three bytes back from the Ziv can be hashed and */ /* entered into the hash table. (This enables the decompressor to keep */ /* pace). See the description and code for more details. */ /* */ /******************************************************************************/ /* */ /* DEFINITION OF COMPRESSED FILE FORMAT */ /* ==================================== */ /* * A compressed file consists of a COPY FLAG followed by a REMAINDER. */ /* * The copy flag CF uses up four bytes with the first byte being the */ /* least significant. */ /* * If CF=1, then the compressed file represents the remainder of the file */ /* exactly. Otherwise CF=0 and the remainder of the file consists of zero */ /* or more GROUPS, each of which represents one or more bytes. */ /* * Each group consists of two bytes of CONTROL information followed by */ /* sixteen ITEMs except for the last group which can contain from one */ /* to sixteen items. */ /* * An item can be either a LITERAL item or a COPY item. */ /* * Each item corresponds to a bit in the control bytes. */ /* * The first control byte corresponds to the first 8 items in the group */ /* with bit 0 corresponding to the first item in the group and bit 7 to */ /* the eighth item in the group. */ /* * The second control byte corresponds to the second 8 items in the group */ /* with bit 0 corresponding to the ninth item in the group and bit 7 to */ /* the sixteenth item in the group. */ /* * A zero bit in a control word means that the corresponding item is a */ /* literal item. A one bit corresponds to a copy item. */ /* * A literal item consists of a single byte which represents itself. */ /* * A copy item consists of two bytes that represent from 3 to 18 bytes. */ /* * The first byte in a copy item will be denoted C1. */ /* * The second byte in a copy item will be denoted C2. */ /* * Bits will be selected using square brackets. */ /* For example: C1[0..3] is the low nibble of the first control byte. */ /* of copy item C1. */ /* * The LENGTH of a copy item is defined to be C1[0..3]+3 which is a number */ /* in the range [3,18]. */ /* * The INDEX of a copy item is defined to be C1[4..7]*256+C2[0..8] which */ /* is a number in the range [0,4095]. */ /* * A copy item represents the sequence of bytes */ /* text[POS-OFFSET..POS-OFFSET+LENGTH-1] where */ /* text is the entire text of the uncompressed string. */ /* POS is the index in the text of the character following the */ /* string represented by all the items preceeding the item */ /* being defined. */ /* OFFSET is obtained from INDEX by looking up the hash table. */ /* */ /******************************************************************************/ /* The following #define defines the length of the copy flag that appears at */ /* the start of the compressed file. The value of four bytes was chosen */ /* because the fast_copy routine on my Macintosh runs faster if the source */ /* and destination blocks are relatively longword aligned. */ /* The actual flag data appears in the first byte. The rest are zeroed so as */ /* to normalize the compressed representation (i.e. not non-deterministic). */ #define FLAG_BYTES 4 /* The following #defines define the meaning of the values of the copy */ /* flag at the start of the compressed file. */ #define FLAG_COMPRESS 0 /* Signals that output was result of compression. */ #define FLAG_COPY 1 /* Signals that output was simply copied over. */ /* The 68000 microprocessor (on which this algorithm was originally developed */ /* is fussy about non-aligned arrays of words. To avoid these problems the */ /* following macro can be used to "waste" from 0 to 3 bytes so as to align */ /* the argument pointer. */ #define ULONG_ALIGN_UP(X) ((((ULONG)X)+sizeof(ULONG)-1)&~(sizeof(ULONG)-1)) /* The following constant defines the maximum length of an uncompressed item. */ /* This definition must not be changed; its value is hardwired into the code. */ /* The longest number of bytes that can be spanned by a single item is 18 */ /* for the longest copy item. */ #define MAX_RAW_ITEM (18) /* The following constant defines the maximum length of an uncompressed group.*/ /* This definition must not be changed; its value is hardwired into the code. */ /* A group contains at most 16 items which explains this definition. */ #define MAX_RAW_GROUP (16*MAX_RAW_ITEM) /* The following constant defines the maximum length of a compressed group. */ /* This definition must not be changed; its value is hardwired into the code. */ /* A compressed group consists of two control bytes followed by up to 16 */ /* compressed items each of which can have a maximum length of two bytes. */ #define MAX_CMP_GROUP (2+16*2) /* The following constant defines the number of entries in the hash table. */ /* This definition must not be changed; its value is hardwired into the code. */ #define HASH_TABLE_LENGTH (4096) /* LZRW3, unlike LZRW1(-A), must initialize its hash table so as to enable */ /* the compressor and decompressor to stay in step maintaining identical hash */ /* tables. In an early version of the algorithm, the tables were simply */ /* initialized to zero and a check for zero was included just before the */ /* matching code. However, this test costs time. A better solution is to */ /* initialize all the entries in the hash table to point to a constant */ /* string. The decompressor does the same. This solution requires no extra */ /* test. The contents of the string do not matter so long as the string is */ /* the same for the compressor and decompressor and contains at least */ /* MAX_RAW_ITEM bytes. I chose consecutive decimal digits because they do not */ /* have white space problems (e.g. there is no chance that the compiler will */ /* replace more than one space by a TAB) and because they make the length of */ /* the string obvious by inspection. */ #define START_STRING_18 ((UBYTE *) "123456789012345678") /* In this algorithm, hash values have to be calculated at more than one */ /* point. The following macro neatens the code up for this. */ #define HASH(PTR) \ (((40543*(((*(PTR))<<8)^((*((PTR)+1))<<4)^(*((PTR)+2))))>>4) & 0xFFF) /******************************************************************************/ LOCAL void compress_compress (p_wrk_mem,p_src_first,src_len,p_dst_first,p_dst_len) /* Input : Hand over the required amount of working memory in p_wrk_mem. */ /* Input : Specify input block using p_src_first and src_len. */ /* Input : Point p_dst_first to the start of the output zone (OZ). */ /* Input : Point p_dst_len to a ULONG to receive the output length. */ /* Input : Input block and output zone must not overlap. */ /* Output : Length of output block written to *p_dst_len. */ /* Output : Output block in Mem[p_dst_first..p_dst_first+*p_dst_len-1]. May */ /* Output : write in OZ=Mem[p_dst_first..p_dst_first+src_len+MAX_CMP_GROUP-1].*/ /* Output : Upon completion guaranteed *p_dst_len<=src_len+FLAG_BYTES. */ UBYTE *p_wrk_mem; UBYTE *p_src_first; ULONG src_len; UBYTE *p_dst_first; LONG *p_dst_len; { /* p_src and p_dst step through the source and destination blocks. */ register UBYTE *p_src = p_src_first; register UBYTE *p_dst = p_dst_first; /* The following variables are never modified and are used in the */ /* calculations that determine when the main loop terminates. */ UBYTE *p_src_post = p_src_first+src_len; UBYTE *p_dst_post = p_dst_first+src_len; UBYTE *p_src_max1 = p_src_first+src_len-MAX_RAW_ITEM; UBYTE *p_src_max16 = p_src_first+src_len-MAX_RAW_ITEM*16; /* The variables 'p_control' and 'control' are used to buffer control bits. */ /* Before each group is processed, the next two bytes of the output block */ /* are set aside for the control word for the group about to be processed. */ /* 'p_control' is set to point to the first byte of that word. Meanwhile, */ /* 'control' buffers the control bits being generated during the processing */ /* of the group. Instead of having a counter to keep track of how many items */ /* have been processed (=the number of bits in the control word), at the */ /* start of each group, the top word of 'control' is filled with 1 bits. */ /* As 'control' is shifted for each item, the 1 bits in the top word are */ /* absorbed or destroyed. When they all run out (i.e. when the top word is */ /* all zero bits, we know that we are at the end of a group. */ # define TOPWORD 0xFFFF0000 UBYTE *p_control; register ULONG control=TOPWORD; /* THe variable 'hash' always points to the first element of the hash table. */ UBYTE **hash= (UBYTE **) ULONG_ALIGN_UP(p_wrk_mem); /* The following two variables represent the literal buffer. p_h1 points to */ /* the hash table entry corresponding to the youngest literal. p_h2 points */ /* to the hash table entry corresponding to the second youngest literal. */ /* Note: p_h1=0=>p_h2=0 because zero values denote absence of a pending */ /* literal. The variables are initialized to zero meaning an empty "buffer". */ UBYTE **p_h1=0; UBYTE **p_h2=0; /* To start, we write the flag bytes. Being optimistic, we set the flag to */ /* FLAG_COMPRESS. The remaining flag bytes are zeroed so as to keep the */ /* algorithm deterministic. */ *p_dst++=FLAG_COMPRESS; {UWORD i; for (i=2;i<=FLAG_BYTES;i++) *p_dst++=0;} /* Reserve the first word of output as the control word for the first group. */ /* Note: This is undone at the end if the input block is empty. */ p_control=p_dst; p_dst+=2; /* Initialize all elements of the hash table to point to a constant string. */ /* Use of an unrolled loop speeds this up considerably. */ {UWORD i; UBYTE **p_h=hash; # define ZH *p_h++=START_STRING_18 for (i=0;i<256;i++) /* 256=HASH_TABLE_LENGTH/16. */ {ZH;ZH;ZH;ZH; ZH;ZH;ZH;ZH; ZH;ZH;ZH;ZH; ZH;ZH;ZH;ZH;} } /* The main loop processes either 1 or 16 items per iteration. As its */ /* termination logic is complicated, I have opted for an infinite loop */ /* structure containing 'break' and 'goto' statements. */ while (TRUE) {/* Begin main processing loop. */ /* Note: All the variables here except unroll should be defined within */ /* the inner loop. Unfortunately the loop hasn't got a block. */ register UBYTE *p; /* Scans through targ phrase during matching. */ register UBYTE *p_ziv= NULL ; /* Points to first byte of current Ziv. */ register UWORD unroll; /* Loop counter for unrolled inner loop. */ register UWORD index; /* Index of current hash table entry. */ register UBYTE **p_h0 = NULL ; /* Pointer to current hash table entry. */ /* Test for overrun and jump to overrun code if necessary. */ if (p_dst>p_dst_post) goto overrun; /* The following cascade of if statements efficiently catches and deals */ /* with varying degrees of closeness to the end of the input block. */ /* When we get very close to the end, we stop updating the table and */ /* code the remaining bytes as literals. This makes the code simpler. */ unroll=16; if (p_src>p_src_max16) { unroll=1; if (p_src>p_src_max1) { if (p_src==p_src_post) break; else goto literal; } } /* This inner unrolled loop processes 'unroll' (whose value is either 1 */ /* or 16) items. I have chosen to implement this loop with labels and */ /* gotos to heighten the ease with which the loop may be implemented with */ /* a single decrement and branch instruction in assembly language and */ /* also because the labels act as highly readable place markers. */ /* (Also because we jump into the loop for endgame literals (see above)). */ begin_unrolled_loop: /* To process the next phrase, we hash the next three bytes and use */ /* the resultant hash table index to look up the hash table. A pointer */ /* to the entry is stored in p_h0 so as to avoid an array lookup. The */ /* hash table entry *p_h0 is looked up yielding a pointer p to a */ /* potential match of the Ziv in the history. */ index=HASH(p_src); p_h0=&hash[index]; p=*p_h0; /* Having looked up the candidate position, we are in a position to */ /* attempt a match. The match loop has been unrolled using the PS */ /* macro so that failure within the first three bytes automatically */ /* results in the literal branch being taken. The coding is simple. */ /* p_ziv saves p_src so we can let p_src wander. */ # define PS *p++!=*p_src++ p_ziv=p_src; if (PS || PS || PS) { /* Literal. */ /* Code the literal byte as itself and a zero control bit. */ p_src=p_ziv; literal: *p_dst++=*p_src++; control&=0xFFFEFFFF; /* We have just coded a literal. If we had two pending ones, that */ /* makes three and we can update the hash table. */ if (p_h2!=0) {*p_h2=p_ziv-2;} /* In any case, rotate the hash table pointers for next time. */ p_h2=p_h1; p_h1=p_h0; } else { /* Copy */ /* Match up to 15 remaining bytes using an unrolled loop and code. */ #if 0 PS || PS || PS || PS || PS || PS || PS || PS || PS || PS || PS || PS || PS || PS || PS || p_src++; #else if ( !( PS || PS || PS || PS || PS || PS || PS || PS || PS || PS || PS || PS || PS || PS || PS ) ) p_src++; #endif *p_dst++=((index&0xF00)>>4)|(--p_src-p_ziv-3); *p_dst++=index&0xFF; /* As we have just coded three bytes, we are now in a position to */ /* update the hash table with the literal bytes that were pending */ /* upon the arrival of extra context bytes. */ if (p_h1!=0) { if (p_h2!=0) {*p_h2=p_ziv-2; p_h2=0;} *p_h1=p_ziv-1; p_h1=0; } /* In any case, we can update the hash table based on the current */ /* position as we just coded at least three bytes in a copy items. */ *p_h0=p_ziv; } control>>=1; /* This loop is all set up for a decrement and jump instruction! */ #ifndef linux ` end_unrolled_loop: if (--unroll) goto begin_unrolled_loop; #else /* end_unrolled_loop: */ if (--unroll) goto begin_unrolled_loop; #endif /* At this point it will nearly always be the end of a group in which */ /* case, we have to do some control-word processing. However, near the */ /* end of the input block, the inner unrolled loop is only executed once. */ /* This necessitates the 'if' test. */ if ((control&TOPWORD)==0) { /* Write the control word to the place we saved for it in the output. */ *p_control++= control &0xFF; *p_control = (control>>8) &0xFF; /* Reserve the next word in the output block for the control word */ /* for the group about to be processed. */ p_control=p_dst; p_dst+=2; /* Reset the control bits buffer. */ control=TOPWORD; } } /* End main processing loop. */ /* After the main processing loop has executed, all the input bytes have */ /* been processed. However, the control word has still to be written to the */ /* word reserved for it in the output at the start of the most recent group. */ /* Before writing, the control word has to be shifted so that all the bits */ /* are in the right place. The "empty" bit positions are filled with 1s */ /* which partially fill the top word. */ while(control&TOPWORD) control>>=1; *p_control++= control &0xFF; *p_control++=(control>>8) &0xFF; /* If the last group contained no items, delete the control word too. */ if (p_control==p_dst) p_dst-=2; /* Write the length of the output block to the dst_len parameter and return. */ *p_dst_len=p_dst-p_dst_first; return; /* Jump here as soon as an overrun is detected. An overrun is defined to */ /* have occurred if p_dst>p_dst_first+src_len. That is, the moment the */ /* length of the output written so far exceeds the length of the input block.*/ /* The algorithm checks for overruns at least at the end of each group */ /* which means that the maximum overrun is MAX_CMP_GROUP bytes. */ /* Once an overrun occurs, the only thing to do is to set the copy flag and */ /* copy the input over. */ overrun: #if 0 *p_dst_first=FLAG_COPY; fast_copy(p_src_first,p_dst_first+FLAG_BYTES,src_len); *p_dst_len=src_len+FLAG_BYTES; #else fast_copy(p_src_first,p_dst_first,src_len); *p_dst_len= -src_len; /* return a negative number to indicate uncompressed data */ #endif } /******************************************************************************/ LOCAL void compress_decompress (p_wrk_mem,p_src_first,src_len,p_dst_first,p_dst_len) /* Input : Hand over the required amount of working memory in p_wrk_mem. */ /* Input : Specify input block using p_src_first and src_len. */ /* Input : Point p_dst_first to the start of the output zone. */ /* Input : Point p_dst_len to a ULONG to receive the output length. */ /* Input : Input block and output zone must not overlap. User knows */ /* Input : upperbound on output block length from earlier compression. */ /* Input : In any case, maximum expansion possible is nine times. */ /* Output : Length of output block written to *p_dst_len. */ /* Output : Output block in Mem[p_dst_first..p_dst_first+*p_dst_len-1]. */ /* Output : Writes only in Mem[p_dst_first..p_dst_first+*p_dst_len-1]. */ UBYTE *p_wrk_mem; UBYTE *p_src_first; LONG src_len; UBYTE *p_dst_first; ULONG *p_dst_len; { /* Byte pointers p_src and p_dst scan through the input and output blocks. */ register UBYTE *p_src = p_src_first+FLAG_BYTES; register UBYTE *p_dst = p_dst_first; /* we need to avoid a SEGV when trying to uncompress corrupt data */ register UBYTE *p_dst_post = p_dst_first + *p_dst_len; /* The following two variables are never modified and are used to control */ /* the main loop. */ UBYTE *p_src_post = p_src_first+src_len; UBYTE *p_src_max16 = p_src_first+src_len-(MAX_CMP_GROUP-2); /* The hash table is the only resident of the working memory. The hash table */ /* contains HASH_TABLE_LENGTH=4096 pointers to positions in the history. To */ /* keep Macintoshes happy, it is longword aligned. */ UBYTE **hash = (UBYTE **) ULONG_ALIGN_UP(p_wrk_mem); /* The variable 'control' is used to buffer the control bits which appear in */ /* groups of 16 bits (control words) at the start of each compressed group. */ /* When each group is read, bit 16 of the register is set to one. Whenever */ /* a new bit is needed, the register is shifted right. When the value of the */ /* register becomes 1, we know that we have reached the end of a group. */ /* Initializing the register to 1 thus instructs the code to follow that it */ /* should read a new control word immediately. */ register ULONG control=1; /* The value of 'literals' is always in the range 0..3. It is the number of */ /* consecutive literal items just seen. We have to record this number so as */ /* to know when to update the hash table. When literals gets to 3, there */ /* have been three consecutive literals and we can update at the position of */ /* the oldest of the three. */ register UWORD literals=0; /* Check the leading copy flag to see if the compressor chose to use a copy */ /* operation instead of a compression operation. If a copy operation was */ /* used, then all we need to do is copy the data over, set the output length */ /* and return. */ #if 0 if (*p_src_first==FLAG_COPY) { fast_copy(p_src_first+FLAG_BYTES,p_dst_first,src_len-FLAG_BYTES); *p_dst_len=src_len-FLAG_BYTES; return; } #else if ( src_len < 0 ) { fast_copy(p_src_first,p_dst_first,-src_len ); *p_dst_len = (ULONG)-src_len; return; } #endif /* Initialize all elements of the hash table to point to a constant string. */ /* Use of an unrolled loop speeds this up considerably. */ {UWORD i; UBYTE **p_h=hash; # define ZJ *p_h++=START_STRING_18 for (i=0;i<256;i++) /* 256=HASH_TABLE_LENGTH/16. */ {ZJ;ZJ;ZJ;ZJ; ZJ;ZJ;ZJ;ZJ; ZJ;ZJ;ZJ;ZJ; ZJ;ZJ;ZJ;ZJ;} } /* The outer loop processes either 1 or 16 items per iteration depending on */ /* how close p_src is to the end of the input block. */ while (p_src!=p_src_post) {/* Start of outer loop */ register UWORD unroll; /* Counts unrolled loop executions. */ /* When 'control' has the value 1, it means that the 16 buffered control */ /* bits that were read in at the start of the current group have all been */ /* shifted out and that all that is left is the 1 bit that was injected */ /* into bit 16 at the start of the current group. When we reach the end */ /* of a group, we have to load a new control word and inject a new 1 bit. */ if (control==1) { control=0x10000|*p_src++; control|=(*p_src++)<<8; } /* If it is possible that we are within 16 groups from the end of the */ /* input, execute the unrolled loop only once, else process a whole group */ /* of 16 items by looping 16 times. */ unroll= p_src<=p_src_max16 ? 16 : 1; /* This inner loop processes one phrase (item) per iteration. */ while (unroll--) { /* Begin unrolled inner loop. */ /* Process a literal or copy item depending on the next control bit. */ if (control&1) { /* Copy item. */ register UBYTE *p; /* Points to place from which to copy. */ register UWORD lenmt; /* Length of copy item minus three. */ register UBYTE **p_hte; /* Pointer to current hash table entry.*/ register UBYTE *p_ziv=p_dst; /* Pointer to start of current Ziv. */ /* Read and dismantle the copy word. Work out from where to copy. */ lenmt=*p_src++; p_hte=&hash[((lenmt&0xF0)<<4)|*p_src++]; p=*p_hte; lenmt&=0xF; /* Now perform the copy using a half unrolled loop. */ *p_dst++=*p++; *p_dst++=*p++; *p_dst++=*p++; while (lenmt--) *p_dst++=*p++; /* Because we have just received 3 or more bytes in a copy item */ /* (whose bytes we have just installed in the output), we are now */ /* in a position to flush all the pending literal hashings that had */ /* been postponed for lack of bytes. */ if (literals>0) { register UBYTE *r=p_ziv-literals;; hash[HASH(r)]=r; if (literals==2) {r++; hash[HASH(r)]=r;} literals=0; } /* In any case, we can immediately update the hash table with the */ /* current position. We don't need to do a HASH(...) to work out */ /* where to put the pointer, as the compressor just told us!!! */ *p_hte=p_ziv; } else { /* Literal item. */ /* Copy over the literal byte. */ *p_dst++=*p_src++; /* If we now have three literals waiting to be hashed into the hash */ /* table, we can do one of them now (because there are three). */ if (++literals == 3) {register UBYTE *p=p_dst-3; hash[HASH(p)]=p; literals=2;} } /* Shift the control buffer so the next control bit is in bit 0. */ control>>=1; #if 1 if (p_dst > p_dst_post) { /* Shit: we tried to decompress corrupt data */ *p_dst_len = 0; return; } #endif } /* End unrolled inner loop. */ } /* End of outer loop */ /* Write the length of the decompressed data before returning. */ *p_dst_len=p_dst-p_dst_first; } /******************************************************************************/ /* End of LZRW3.C */ /******************************************************************************/ |