| /* | |
| * $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( | |
| 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) | |
| /******************************************************************************/ | |
| /* 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. */ | |
| LOCAL void compress_compress(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=NULL; | |
| UBYTE **p_h2=NULL; | |
| /* 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) | |
| {*p_h2=p_ziv-2; p_h2=NULL;} | |
| *p_h1=p_ziv-1; p_h1=NULL; | |
| } | |
| /* 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 | |
| } | |
| /******************************************************************************/ | |
| /* 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]. */ | |
| LOCAL void compress_decompress( 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 */ | |
| /******************************************************************************/ |