/* * $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 */ /******************************************************************************/