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Diffstat (limited to 'drivers/char/ftape/compressor/lzrw3.c')
| -rw-r--r-- | drivers/char/ftape/compressor/lzrw3.c | 743 |
1 files changed, 743 insertions, 0 deletions
diff --git a/drivers/char/ftape/compressor/lzrw3.c b/drivers/char/ftape/compressor/lzrw3.c new file mode 100644 index 00000000000..a032a0ee2a9 --- /dev/null +++ b/drivers/char/ftape/compressor/lzrw3.c @@ -0,0 +1,743 @@ +/* + * $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 */ +/******************************************************************************/ |