diff options
Diffstat (limited to 'drivers/char/ftape/compressor/lzrw3.c')
| -rw-r--r-- | drivers/char/ftape/compressor/lzrw3.c | 743 |
1 files changed, 0 insertions, 743 deletions
diff --git a/drivers/char/ftape/compressor/lzrw3.c b/drivers/char/ftape/compressor/lzrw3.c deleted file mode 100644 index a032a0ee2a99..000000000000 --- a/drivers/char/ftape/compressor/lzrw3.c +++ /dev/null @@ -1,743 +0,0 @@ -/* - * $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 */ -/******************************************************************************/ |
