patch-2.1.66 linux/drivers/char/ftape/compressor/lzrw3.c
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- Lines: 751
- Date:
Tue Nov 25 14:45:27 1997
- Orig file:
v2.1.65/linux/drivers/char/ftape/compressor/lzrw3.c
- Orig date:
Wed Dec 31 16:00:00 1969
diff -u --recursive --new-file v2.1.65/linux/drivers/char/ftape/compressor/lzrw3.c linux/drivers/char/ftape/compressor/lzrw3.c
@@ -0,0 +1,750 @@
+/*
+ * $Source: /homes/cvs/ftape-stacked/ftape/compressor/lzrw3.c,v $
+ * $Revision: 1.1 $
+ * $Date: 1997/10/05 19:12:29 $
+ *
+ * Implementation of Ross Williams lzrw3 algorithm. Adaption for zftape.
+ *
+ */
+
+#include "../compressor/lzrw3.h" /* Defines single exported function "compress". */
+
+/******************************************************************************/
+/* */
+/* LZRW3.C */
+/* */
+/******************************************************************************/
+/* */
+/* Author : Ross Williams. */
+/* Date : 30-Jun-1991. */
+/* Release : 1. */
+/* */
+/******************************************************************************/
+/* */
+/* This file contains an implementation of the LZRW3 data compression */
+/* algorithm in C. */
+/* */
+/* The algorithm is a general purpose compression algorithm that runs fast */
+/* and gives reasonable compression. The algorithm is a member of the Lempel */
+/* Ziv family of algorithms and bases its compression on the presence in the */
+/* data of repeated substrings. */
+/* */
+/* This algorithm is unpatented and the code is public domain. As the */
+/* algorithm is based on the LZ77 class of algorithms, it is unlikely to be */
+/* the subject of a patent challenge. */
+/* */
+/* Unlike the LZRW1 and LZRW1-A algorithms, the LZRW3 algorithm is */
+/* deterministic and is guaranteed to yield the same compressed */
+/* representation for a given file each time it is run. */
+/* */
+/* The LZRW3 algorithm was originally designed and implemented */
+/* by Ross Williams on 31-Dec-1990. */
+/* */
+/* Here are the results of applying this code, compiled under THINK C 4.0 */
+/* and running on a Mac-SE (8MHz 68000), to the standard calgary corpus. */
+/* */
+/* +----------------------------------------------------------------+ */
+/* | DATA COMPRESSION TEST | */
+/* | ===================== | */
+/* | Time of run : Sun 30-Jun-1991 09:31PM | */
+/* | Timing accuracy : One part in 100 | */
+/* | Context length : 262144 bytes (= 256.0000K) | */
+/* | Test suite : Calgary Corpus Suite | */
+/* | Files in suite : 14 | */
+/* | Algorithm : LZRW3 | */
+/* | Note: All averages are calculated from the un-rounded values. | */
+/* +----------------------------------------------------------------+ */
+/* | File Name Length CxB ComLen %Remn Bits Com K/s Dec K/s | */
+/* | ---------- ------ --- ------ ----- ---- ------- ------- | */
+/* | rpus:Bib.D 111261 1 55033 49.5 3.96 19.46 32.27 | */
+/* | us:Book1.D 768771 3 467962 60.9 4.87 17.03 31.07 | */
+/* | us:Book2.D 610856 3 317102 51.9 4.15 19.39 34.15 | */
+/* | rpus:Geo.D 102400 1 82424 80.5 6.44 11.65 18.18 | */
+/* | pus:News.D 377109 2 205670 54.5 4.36 17.14 27.47 | */
+/* | pus:Obj1.D 21504 1 13027 60.6 4.85 13.40 18.95 | */
+/* | pus:Obj2.D 246814 1 116286 47.1 3.77 19.31 30.10 | */
+/* | s:Paper1.D 53161 1 27522 51.8 4.14 18.60 31.15 | */
+/* | s:Paper2.D 82199 1 45160 54.9 4.40 18.45 32.84 | */
+/* | rpus:Pic.D 513216 2 122388 23.8 1.91 35.29 51.05 | */
+/* | us:Progc.D 39611 1 19669 49.7 3.97 18.87 30.64 | */
+/* | us:Progl.D 71646 1 28247 39.4 3.15 24.34 40.66 | */
+/* | us:Progp.D 49379 1 19377 39.2 3.14 23.91 39.23 | */
+/* | us:Trans.D 93695 1 33481 35.7 2.86 25.48 40.37 | */
+/* +----------------------------------------------------------------+ */
+/* | Average 224401 1 110953 50.0 4.00 20.17 32.72 | */
+/* +----------------------------------------------------------------+ */
+/* */
+/******************************************************************************/
+
+/******************************************************************************/
+
+/* The following structure is returned by the "compress" function below when */
+/* the user asks the function to return identifying information. */
+/* The most important field in the record is the working memory field which */
+/* tells the calling program how much working memory should be passed to */
+/* "compress" when it is called to perform a compression or decompression. */
+/* LZRW3 uses the same amount of memory during compression and decompression. */
+/* For more information on this structure see "compress.h". */
+
+#define U(X) ((ULONG) X)
+#define SIZE_P_BYTE (U(sizeof(UBYTE *)))
+#define SIZE_WORD (U(sizeof(UWORD )))
+#define ALIGNMENT_FUDGE (U(16))
+#define MEM_REQ ( U(4096)*(SIZE_P_BYTE) + ALIGNMENT_FUDGE )
+
+static struct compress_identity identity =
+{
+ U(0x032DDEA8), /* Algorithm identification number. */
+ MEM_REQ, /* Working memory (bytes) required. */
+ "LZRW3", /* Name of algorithm. */
+ "1.0", /* Version number of algorithm. */
+ "31-Dec-1990", /* Date of algorithm. */
+ "Public Domain", /* Copyright notice. */
+ "Ross N. Williams", /* Author of algorithm. */
+ "Renaissance Software", /* Affiliation of author. */
+ "Public Domain" /* Vendor of algorithm. */
+};
+
+LOCAL void compress_compress (UBYTE *,UBYTE *,ULONG,UBYTE *, LONG *);
+LOCAL void compress_decompress(UBYTE *,UBYTE *,LONG, UBYTE *, ULONG *);
+
+/******************************************************************************/
+
+/* This function is the only function exported by this module. */
+/* Depending on its first parameter, the function can be requested to */
+/* compress a block of memory, decompress a block of memory, or to identify */
+/* itself. For more information, see the specification file "compress.h". */
+
+EXPORT void lzrw3_compress(action,wrk_mem,src_adr,src_len,dst_adr,p_dst_len)
+UWORD action; /* Action to be performed. */
+UBYTE *wrk_mem; /* Address of working memory we can use. */
+UBYTE *src_adr; /* Address of input data. */
+LONG src_len; /* Length of input data. */
+UBYTE *dst_adr; /* Address to put output data. */
+void *p_dst_len; /* Address of longword for length of output data. */
+{
+ switch (action)
+ {
+ case COMPRESS_ACTION_IDENTITY:
+ *((struct compress_identity **)p_dst_len)= &identity;
+ break;
+ case COMPRESS_ACTION_COMPRESS:
+ compress_compress(wrk_mem,src_adr,src_len,dst_adr,(LONG *)p_dst_len);
+ break;
+ case COMPRESS_ACTION_DECOMPRESS:
+ compress_decompress(wrk_mem,src_adr,src_len,dst_adr,(LONG *)p_dst_len);
+ break;
+ }
+}
+
+/******************************************************************************/
+/* */
+/* BRIEF DESCRIPTION OF THE LZRW3 ALGORITHM */
+/* ======================================== */
+/* The LZRW3 algorithm is identical to the LZRW1-A algorithm except that */
+/* instead of transmitting history offsets, it transmits hash table indexes. */
+/* In order to decode the indexes, the decompressor must maintain an */
+/* identical hash table. Copy items are straightforward:when the decompressor */
+/* receives a copy item, it simply looks up the hash table to translate the */
+/* index into a pointer into the data already decompressed. To update the */
+/* hash table, it replaces the same table entry with a pointer to the start */
+/* of the newly decoded phrase. The tricky part is with literal items, for at */
+/* the time that the decompressor receives a literal item the decompressor */
+/* does not have the three bytes in the Ziv (that the compressor has) to */
+/* perform the three-byte hash. To solve this problem, in LZRW3, both the */
+/* compressor and decompressor are wired up so that they "buffer" these */
+/* literals and update their hash tables only when three bytes are available. */
+/* This makes the maximum buffering 2 bytes. */
+/* */
+/* Replacement of offsets by hash table indexes yields a few percent extra */
+/* compression at the cost of some speed. LZRW3 is slower than LZRW1, LZRW1-A */
+/* and LZRW2, but yields better compression. */
+/* */
+/* Extra compression could be obtained by using a hash table of depth two. */
+/* However, increasing the depth above one incurs a significant decrease in */
+/* compression speed which was not considered worthwhile. Another reason for */
+/* keeping the depth down to one was to allow easy comparison with the */
+/* LZRW1-A and LZRW2 algorithms so as to demonstrate the exact effect of the */
+/* use of direct hash indexes. */
+/* */
+/* +---+ */
+/* |___|4095 */
+/* |___| */
+/* +---------------------*_|<---+ /----+---\ */
+/* | |___| +---|Hash | */
+/* | |___| |Function| */
+/* | |___| \--------/ */
+/* | |___|0 ^ */
+/* | +---+ | */
+/* | Hash +-----+ */
+/* | Table | */
+/* | --- */
+/* v ^^^ */
+/* +-------------------------------------|----------------+ */
+/* |||||||||||||||||||||||||||||||||||||||||||||||||||||||| */
+/* +-------------------------------------|----------------+ */
+/* | |1......18| | */
+/* |<------- Lempel=History ------------>|<--Ziv-->| | */
+/* | (=bytes already processed) |<-Still to go-->| */
+/* |<-------------------- INPUT BLOCK ------------------->| */
+/* */
+/* The diagram above for LZRW3 looks almost identical to the diagram for */
+/* LZRW1. The difference is that in LZRW3, the compressor transmits hash */
+/* table indices instead of Lempel offsets. For this to work, the */
+/* decompressor must maintain a hash table as well as the compressor and both */
+/* compressor and decompressor must "buffer" literals, as the decompressor */
+/* cannot hash phrases commencing with a literal until another two bytes have */
+/* arrived. */
+/* */
+/* LZRW3 Algorithm Execution Summary */
+/* --------------------------------- */
+/* 1. Hash the first three bytes of the Ziv to yield a hash table index h. */
+/* 2. Look up the hash table yielding history pointer p. */
+/* 3. Match where p points with the Ziv. If there is a match of three or */
+/* more bytes, code those bytes (in the Ziv) as a copy item, otherwise */
+/* code the next byte in the Ziv as a literal item. */
+/* 4. Update the hash table as possible subject to the constraint that only */
+/* phrases commencing three bytes back from the Ziv can be hashed and */
+/* entered into the hash table. (This enables the decompressor to keep */
+/* pace). See the description and code for more details. */
+/* */
+/******************************************************************************/
+/* */
+/* DEFINITION OF COMPRESSED FILE FORMAT */
+/* ==================================== */
+/* * A compressed file consists of a COPY FLAG followed by a REMAINDER. */
+/* * The copy flag CF uses up four bytes with the first byte being the */
+/* least significant. */
+/* * If CF=1, then the compressed file represents the remainder of the file */
+/* exactly. Otherwise CF=0 and the remainder of the file consists of zero */
+/* or more GROUPS, each of which represents one or more bytes. */
+/* * Each group consists of two bytes of CONTROL information followed by */
+/* sixteen ITEMs except for the last group which can contain from one */
+/* to sixteen items. */
+/* * An item can be either a LITERAL item or a COPY item. */
+/* * Each item corresponds to a bit in the control bytes. */
+/* * The first control byte corresponds to the first 8 items in the group */
+/* with bit 0 corresponding to the first item in the group and bit 7 to */
+/* the eighth item in the group. */
+/* * The second control byte corresponds to the second 8 items in the group */
+/* with bit 0 corresponding to the ninth item in the group and bit 7 to */
+/* the sixteenth item in the group. */
+/* * A zero bit in a control word means that the corresponding item is a */
+/* literal item. A one bit corresponds to a copy item. */
+/* * A literal item consists of a single byte which represents itself. */
+/* * A copy item consists of two bytes that represent from 3 to 18 bytes. */
+/* * The first byte in a copy item will be denoted C1. */
+/* * The second byte in a copy item will be denoted C2. */
+/* * Bits will be selected using square brackets. */
+/* For example: C1[0..3] is the low nibble of the first control byte. */
+/* of copy item C1. */
+/* * The LENGTH of a copy item is defined to be C1[0..3]+3 which is a number */
+/* in the range [3,18]. */
+/* * The INDEX of a copy item is defined to be C1[4..7]*256+C2[0..8] which */
+/* is a number in the range [0,4095]. */
+/* * A copy item represents the sequence of bytes */
+/* text[POS-OFFSET..POS-OFFSET+LENGTH-1] where */
+/* text is the entire text of the uncompressed string. */
+/* POS is the index in the text of the character following the */
+/* string represented by all the items preceeding the item */
+/* being defined. */
+/* OFFSET is obtained from INDEX by looking up the hash table. */
+/* */
+/******************************************************************************/
+
+/* The following #define defines the length of the copy flag that appears at */
+/* the start of the compressed file. The value of four bytes was chosen */
+/* because the fast_copy routine on my Macintosh runs faster if the source */
+/* and destination blocks are relatively longword aligned. */
+/* The actual flag data appears in the first byte. The rest are zeroed so as */
+/* to normalize the compressed representation (i.e. not non-deterministic). */
+#define FLAG_BYTES 4
+
+/* The following #defines define the meaning of the values of the copy */
+/* flag at the start of the compressed file. */
+#define FLAG_COMPRESS 0 /* Signals that output was result of compression. */
+#define FLAG_COPY 1 /* Signals that output was simply copied over. */
+
+/* The 68000 microprocessor (on which this algorithm was originally developed */
+/* is fussy about non-aligned arrays of words. To avoid these problems the */
+/* following macro can be used to "waste" from 0 to 3 bytes so as to align */
+/* the argument pointer. */
+#define ULONG_ALIGN_UP(X) ((((ULONG)X)+sizeof(ULONG)-1)&~(sizeof(ULONG)-1))
+
+
+/* The following constant defines the maximum length of an uncompressed item. */
+/* This definition must not be changed; its value is hardwired into the code. */
+/* The longest number of bytes that can be spanned by a single item is 18 */
+/* for the longest copy item. */
+#define MAX_RAW_ITEM (18)
+
+/* The following constant defines the maximum length of an uncompressed group.*/
+/* This definition must not be changed; its value is hardwired into the code. */
+/* A group contains at most 16 items which explains this definition. */
+#define MAX_RAW_GROUP (16*MAX_RAW_ITEM)
+
+/* The following constant defines the maximum length of a compressed group. */
+/* This definition must not be changed; its value is hardwired into the code. */
+/* A compressed group consists of two control bytes followed by up to 16 */
+/* compressed items each of which can have a maximum length of two bytes. */
+#define MAX_CMP_GROUP (2+16*2)
+
+/* The following constant defines the number of entries in the hash table. */
+/* This definition must not be changed; its value is hardwired into the code. */
+#define HASH_TABLE_LENGTH (4096)
+
+/* LZRW3, unlike LZRW1(-A), must initialize its hash table so as to enable */
+/* the compressor and decompressor to stay in step maintaining identical hash */
+/* tables. In an early version of the algorithm, the tables were simply */
+/* initialized to zero and a check for zero was included just before the */
+/* matching code. However, this test costs time. A better solution is to */
+/* initialize all the entries in the hash table to point to a constant */
+/* string. The decompressor does the same. This solution requires no extra */
+/* test. The contents of the string do not matter so long as the string is */
+/* the same for the compressor and decompressor and contains at least */
+/* MAX_RAW_ITEM bytes. I chose consecutive decimal digits because they do not */
+/* have white space problems (e.g. there is no chance that the compiler will */
+/* replace more than one space by a TAB) and because they make the length of */
+/* the string obvious by inspection. */
+#define START_STRING_18 ((UBYTE *) "123456789012345678")
+
+/* In this algorithm, hash values have to be calculated at more than one */
+/* point. The following macro neatens the code up for this. */
+#define HASH(PTR) \
+ (((40543*(((*(PTR))<<8)^((*((PTR)+1))<<4)^(*((PTR)+2))))>>4) & 0xFFF)
+
+/******************************************************************************/
+
+LOCAL void compress_compress
+ (p_wrk_mem,p_src_first,src_len,p_dst_first,p_dst_len)
+/* Input : Hand over the required amount of working memory in p_wrk_mem. */
+/* Input : Specify input block using p_src_first and src_len. */
+/* Input : Point p_dst_first to the start of the output zone (OZ). */
+/* Input : Point p_dst_len to a ULONG to receive the output length. */
+/* Input : Input block and output zone must not overlap. */
+/* Output : Length of output block written to *p_dst_len. */
+/* Output : Output block in Mem[p_dst_first..p_dst_first+*p_dst_len-1]. May */
+/* Output : write in OZ=Mem[p_dst_first..p_dst_first+src_len+MAX_CMP_GROUP-1].*/
+/* Output : Upon completion guaranteed *p_dst_len<=src_len+FLAG_BYTES. */
+UBYTE *p_wrk_mem;
+UBYTE *p_src_first;
+ULONG src_len;
+UBYTE *p_dst_first;
+LONG *p_dst_len;
+{
+ /* p_src and p_dst step through the source and destination blocks. */
+ register UBYTE *p_src = p_src_first;
+ register UBYTE *p_dst = p_dst_first;
+
+ /* The following variables are never modified and are used in the */
+ /* calculations that determine when the main loop terminates. */
+ UBYTE *p_src_post = p_src_first+src_len;
+ UBYTE *p_dst_post = p_dst_first+src_len;
+ UBYTE *p_src_max1 = p_src_first+src_len-MAX_RAW_ITEM;
+ UBYTE *p_src_max16 = p_src_first+src_len-MAX_RAW_ITEM*16;
+
+ /* The variables 'p_control' and 'control' are used to buffer control bits. */
+ /* Before each group is processed, the next two bytes of the output block */
+ /* are set aside for the control word for the group about to be processed. */
+ /* 'p_control' is set to point to the first byte of that word. Meanwhile, */
+ /* 'control' buffers the control bits being generated during the processing */
+ /* of the group. Instead of having a counter to keep track of how many items */
+ /* have been processed (=the number of bits in the control word), at the */
+ /* start of each group, the top word of 'control' is filled with 1 bits. */
+ /* As 'control' is shifted for each item, the 1 bits in the top word are */
+ /* absorbed or destroyed. When they all run out (i.e. when the top word is */
+ /* all zero bits, we know that we are at the end of a group. */
+# define TOPWORD 0xFFFF0000
+ UBYTE *p_control;
+ register ULONG control=TOPWORD;
+
+ /* THe variable 'hash' always points to the first element of the hash table. */
+ UBYTE **hash= (UBYTE **) ULONG_ALIGN_UP(p_wrk_mem);
+
+ /* The following two variables represent the literal buffer. p_h1 points to */
+ /* the hash table entry corresponding to the youngest literal. p_h2 points */
+ /* to the hash table entry corresponding to the second youngest literal. */
+ /* Note: p_h1=0=>p_h2=0 because zero values denote absence of a pending */
+ /* literal. The variables are initialized to zero meaning an empty "buffer". */
+ UBYTE **p_h1=0;
+ UBYTE **p_h2=0;
+
+ /* To start, we write the flag bytes. Being optimistic, we set the flag to */
+ /* FLAG_COMPRESS. The remaining flag bytes are zeroed so as to keep the */
+ /* algorithm deterministic. */
+ *p_dst++=FLAG_COMPRESS;
+ {UWORD i; for (i=2;i<=FLAG_BYTES;i++) *p_dst++=0;}
+
+ /* Reserve the first word of output as the control word for the first group. */
+ /* Note: This is undone at the end if the input block is empty. */
+ p_control=p_dst; p_dst+=2;
+
+ /* Initialize all elements of the hash table to point to a constant string. */
+ /* Use of an unrolled loop speeds this up considerably. */
+ {UWORD i; UBYTE **p_h=hash;
+# define ZH *p_h++=START_STRING_18
+ for (i=0;i<256;i++) /* 256=HASH_TABLE_LENGTH/16. */
+ {ZH;ZH;ZH;ZH;
+ ZH;ZH;ZH;ZH;
+ ZH;ZH;ZH;ZH;
+ ZH;ZH;ZH;ZH;}
+ }
+
+ /* The main loop processes either 1 or 16 items per iteration. As its */
+ /* termination logic is complicated, I have opted for an infinite loop */
+ /* structure containing 'break' and 'goto' statements. */
+ while (TRUE)
+ {/* Begin main processing loop. */
+
+ /* Note: All the variables here except unroll should be defined within */
+ /* the inner loop. Unfortunately the loop hasn't got a block. */
+ register UBYTE *p; /* Scans through targ phrase during matching. */
+ register UBYTE *p_ziv= NULL ; /* Points to first byte of current Ziv. */
+ register UWORD unroll; /* Loop counter for unrolled inner loop. */
+ register UWORD index; /* Index of current hash table entry. */
+ register UBYTE **p_h0 = NULL ; /* Pointer to current hash table entry. */
+
+ /* Test for overrun and jump to overrun code if necessary. */
+ if (p_dst>p_dst_post)
+ goto overrun;
+
+ /* The following cascade of if statements efficiently catches and deals */
+ /* with varying degrees of closeness to the end of the input block. */
+ /* When we get very close to the end, we stop updating the table and */
+ /* code the remaining bytes as literals. This makes the code simpler. */
+ unroll=16;
+ if (p_src>p_src_max16)
+ {
+ unroll=1;
+ if (p_src>p_src_max1)
+ {
+ if (p_src==p_src_post)
+ break;
+ else
+ goto literal;
+ }
+ }
+
+ /* This inner unrolled loop processes 'unroll' (whose value is either 1 */
+ /* or 16) items. I have chosen to implement this loop with labels and */
+ /* gotos to heighten the ease with which the loop may be implemented with */
+ /* a single decrement and branch instruction in assembly language and */
+ /* also because the labels act as highly readable place markers. */
+ /* (Also because we jump into the loop for endgame literals (see above)). */
+
+ begin_unrolled_loop:
+
+ /* To process the next phrase, we hash the next three bytes and use */
+ /* the resultant hash table index to look up the hash table. A pointer */
+ /* to the entry is stored in p_h0 so as to avoid an array lookup. The */
+ /* hash table entry *p_h0 is looked up yielding a pointer p to a */
+ /* potential match of the Ziv in the history. */
+ index=HASH(p_src);
+ p_h0=&hash[index];
+ p=*p_h0;
+
+ /* Having looked up the candidate position, we are in a position to */
+ /* attempt a match. The match loop has been unrolled using the PS */
+ /* macro so that failure within the first three bytes automatically */
+ /* results in the literal branch being taken. The coding is simple. */
+ /* p_ziv saves p_src so we can let p_src wander. */
+# define PS *p++!=*p_src++
+ p_ziv=p_src;
+ if (PS || PS || PS)
+ {
+ /* Literal. */
+
+ /* Code the literal byte as itself and a zero control bit. */
+ p_src=p_ziv; literal: *p_dst++=*p_src++; control&=0xFFFEFFFF;
+
+ /* We have just coded a literal. If we had two pending ones, that */
+ /* makes three and we can update the hash table. */
+ if (p_h2!=0)
+ {*p_h2=p_ziv-2;}
+
+ /* In any case, rotate the hash table pointers for next time. */
+ p_h2=p_h1; p_h1=p_h0;
+
+ }
+ else
+ {
+ /* Copy */
+
+ /* Match up to 15 remaining bytes using an unrolled loop and code. */
+#if 0
+ PS || PS || PS || PS || PS || PS || PS || PS ||
+ PS || PS || PS || PS || PS || PS || PS || p_src++;
+#else
+ if (
+ !( PS || PS || PS || PS || PS || PS || PS || PS ||
+ PS || PS || PS || PS || PS || PS || PS )
+ ) p_src++;
+#endif
+ *p_dst++=((index&0xF00)>>4)|(--p_src-p_ziv-3);
+ *p_dst++=index&0xFF;
+
+ /* As we have just coded three bytes, we are now in a position to */
+ /* update the hash table with the literal bytes that were pending */
+ /* upon the arrival of extra context bytes. */
+ if (p_h1!=0)
+ {
+ if (p_h2!=0)
+ {*p_h2=p_ziv-2; p_h2=0;}
+ *p_h1=p_ziv-1; p_h1=0;
+ }
+
+ /* In any case, we can update the hash table based on the current */
+ /* position as we just coded at least three bytes in a copy items. */
+ *p_h0=p_ziv;
+
+ }
+ control>>=1;
+
+ /* This loop is all set up for a decrement and jump instruction! */
+#ifndef linux
+` end_unrolled_loop: if (--unroll) goto begin_unrolled_loop;
+#else
+ /* end_unrolled_loop: */ if (--unroll) goto begin_unrolled_loop;
+#endif
+
+ /* At this point it will nearly always be the end of a group in which */
+ /* case, we have to do some control-word processing. However, near the */
+ /* end of the input block, the inner unrolled loop is only executed once. */
+ /* This necessitates the 'if' test. */
+ if ((control&TOPWORD)==0)
+ {
+ /* Write the control word to the place we saved for it in the output. */
+ *p_control++= control &0xFF;
+ *p_control = (control>>8) &0xFF;
+
+ /* Reserve the next word in the output block for the control word */
+ /* for the group about to be processed. */
+ p_control=p_dst; p_dst+=2;
+
+ /* Reset the control bits buffer. */
+ control=TOPWORD;
+ }
+
+ } /* End main processing loop. */
+
+ /* After the main processing loop has executed, all the input bytes have */
+ /* been processed. However, the control word has still to be written to the */
+ /* word reserved for it in the output at the start of the most recent group. */
+ /* Before writing, the control word has to be shifted so that all the bits */
+ /* are in the right place. The "empty" bit positions are filled with 1s */
+ /* which partially fill the top word. */
+ while(control&TOPWORD) control>>=1;
+ *p_control++= control &0xFF;
+ *p_control++=(control>>8) &0xFF;
+
+ /* If the last group contained no items, delete the control word too. */
+ if (p_control==p_dst) p_dst-=2;
+
+ /* Write the length of the output block to the dst_len parameter and return. */
+ *p_dst_len=p_dst-p_dst_first;
+ return;
+
+ /* Jump here as soon as an overrun is detected. An overrun is defined to */
+ /* have occurred if p_dst>p_dst_first+src_len. That is, the moment the */
+ /* length of the output written so far exceeds the length of the input block.*/
+ /* The algorithm checks for overruns at least at the end of each group */
+ /* which means that the maximum overrun is MAX_CMP_GROUP bytes. */
+ /* Once an overrun occurs, the only thing to do is to set the copy flag and */
+ /* copy the input over. */
+ overrun:
+#if 0
+ *p_dst_first=FLAG_COPY;
+ fast_copy(p_src_first,p_dst_first+FLAG_BYTES,src_len);
+ *p_dst_len=src_len+FLAG_BYTES;
+#else
+ fast_copy(p_src_first,p_dst_first,src_len);
+ *p_dst_len= -src_len; /* return a negative number to indicate uncompressed data */
+#endif
+}
+
+/******************************************************************************/
+
+LOCAL void compress_decompress
+ (p_wrk_mem,p_src_first,src_len,p_dst_first,p_dst_len)
+/* Input : Hand over the required amount of working memory in p_wrk_mem. */
+/* Input : Specify input block using p_src_first and src_len. */
+/* Input : Point p_dst_first to the start of the output zone. */
+/* Input : Point p_dst_len to a ULONG to receive the output length. */
+/* Input : Input block and output zone must not overlap. User knows */
+/* Input : upperbound on output block length from earlier compression. */
+/* Input : In any case, maximum expansion possible is nine times. */
+/* Output : Length of output block written to *p_dst_len. */
+/* Output : Output block in Mem[p_dst_first..p_dst_first+*p_dst_len-1]. */
+/* Output : Writes only in Mem[p_dst_first..p_dst_first+*p_dst_len-1]. */
+UBYTE *p_wrk_mem;
+UBYTE *p_src_first;
+LONG src_len;
+UBYTE *p_dst_first;
+ULONG *p_dst_len;
+{
+ /* Byte pointers p_src and p_dst scan through the input and output blocks. */
+ register UBYTE *p_src = p_src_first+FLAG_BYTES;
+ register UBYTE *p_dst = p_dst_first;
+ /* we need to avoid a SEGV when trying to uncompress corrupt data */
+ register UBYTE *p_dst_post = p_dst_first + *p_dst_len;
+
+ /* The following two variables are never modified and are used to control */
+ /* the main loop. */
+ UBYTE *p_src_post = p_src_first+src_len;
+ UBYTE *p_src_max16 = p_src_first+src_len-(MAX_CMP_GROUP-2);
+
+ /* The hash table is the only resident of the working memory. The hash table */
+ /* contains HASH_TABLE_LENGTH=4096 pointers to positions in the history. To */
+ /* keep Macintoshes happy, it is longword aligned. */
+ UBYTE **hash = (UBYTE **) ULONG_ALIGN_UP(p_wrk_mem);
+
+ /* The variable 'control' is used to buffer the control bits which appear in */
+ /* groups of 16 bits (control words) at the start of each compressed group. */
+ /* When each group is read, bit 16 of the register is set to one. Whenever */
+ /* a new bit is needed, the register is shifted right. When the value of the */
+ /* register becomes 1, we know that we have reached the end of a group. */
+ /* Initializing the register to 1 thus instructs the code to follow that it */
+ /* should read a new control word immediately. */
+ register ULONG control=1;
+
+ /* The value of 'literals' is always in the range 0..3. It is the number of */
+ /* consecutive literal items just seen. We have to record this number so as */
+ /* to know when to update the hash table. When literals gets to 3, there */
+ /* have been three consecutive literals and we can update at the position of */
+ /* the oldest of the three. */
+ register UWORD literals=0;
+
+ /* Check the leading copy flag to see if the compressor chose to use a copy */
+ /* operation instead of a compression operation. If a copy operation was */
+ /* used, then all we need to do is copy the data over, set the output length */
+ /* and return. */
+#if 0
+ if (*p_src_first==FLAG_COPY)
+ {
+ fast_copy(p_src_first+FLAG_BYTES,p_dst_first,src_len-FLAG_BYTES);
+ *p_dst_len=src_len-FLAG_BYTES;
+ return;
+ }
+#else
+ if ( src_len < 0 )
+ {
+ fast_copy(p_src_first,p_dst_first,-src_len );
+ *p_dst_len = (ULONG)-src_len;
+ return;
+ }
+#endif
+
+ /* Initialize all elements of the hash table to point to a constant string. */
+ /* Use of an unrolled loop speeds this up considerably. */
+ {UWORD i; UBYTE **p_h=hash;
+# define ZJ *p_h++=START_STRING_18
+ for (i=0;i<256;i++) /* 256=HASH_TABLE_LENGTH/16. */
+ {ZJ;ZJ;ZJ;ZJ;
+ ZJ;ZJ;ZJ;ZJ;
+ ZJ;ZJ;ZJ;ZJ;
+ ZJ;ZJ;ZJ;ZJ;}
+ }
+
+ /* The outer loop processes either 1 or 16 items per iteration depending on */
+ /* how close p_src is to the end of the input block. */
+ while (p_src!=p_src_post)
+ {/* Start of outer loop */
+
+ register UWORD unroll; /* Counts unrolled loop executions. */
+
+ /* When 'control' has the value 1, it means that the 16 buffered control */
+ /* bits that were read in at the start of the current group have all been */
+ /* shifted out and that all that is left is the 1 bit that was injected */
+ /* into bit 16 at the start of the current group. When we reach the end */
+ /* of a group, we have to load a new control word and inject a new 1 bit. */
+ if (control==1)
+ {
+ control=0x10000|*p_src++;
+ control|=(*p_src++)<<8;
+ }
+
+ /* If it is possible that we are within 16 groups from the end of the */
+ /* input, execute the unrolled loop only once, else process a whole group */
+ /* of 16 items by looping 16 times. */
+ unroll= p_src<=p_src_max16 ? 16 : 1;
+
+ /* This inner loop processes one phrase (item) per iteration. */
+ while (unroll--)
+ { /* Begin unrolled inner loop. */
+
+ /* Process a literal or copy item depending on the next control bit. */
+ if (control&1)
+ {
+ /* Copy item. */
+
+ register UBYTE *p; /* Points to place from which to copy. */
+ register UWORD lenmt; /* Length of copy item minus three. */
+ register UBYTE **p_hte; /* Pointer to current hash table entry.*/
+ register UBYTE *p_ziv=p_dst; /* Pointer to start of current Ziv. */
+
+ /* Read and dismantle the copy word. Work out from where to copy. */
+ lenmt=*p_src++;
+ p_hte=&hash[((lenmt&0xF0)<<4)|*p_src++];
+ p=*p_hte;
+ lenmt&=0xF;
+
+ /* Now perform the copy using a half unrolled loop. */
+ *p_dst++=*p++;
+ *p_dst++=*p++;
+ *p_dst++=*p++;
+ while (lenmt--)
+ *p_dst++=*p++;
+
+ /* Because we have just received 3 or more bytes in a copy item */
+ /* (whose bytes we have just installed in the output), we are now */
+ /* in a position to flush all the pending literal hashings that had */
+ /* been postponed for lack of bytes. */
+ if (literals>0)
+ {
+ register UBYTE *r=p_ziv-literals;;
+ hash[HASH(r)]=r;
+ if (literals==2)
+ {r++; hash[HASH(r)]=r;}
+ literals=0;
+ }
+
+ /* In any case, we can immediately update the hash table with the */
+ /* current position. We don't need to do a HASH(...) to work out */
+ /* where to put the pointer, as the compressor just told us!!! */
+ *p_hte=p_ziv;
+
+ }
+ else
+ {
+ /* Literal item. */
+
+ /* Copy over the literal byte. */
+ *p_dst++=*p_src++;
+
+ /* If we now have three literals waiting to be hashed into the hash */
+ /* table, we can do one of them now (because there are three). */
+ if (++literals == 3)
+ {register UBYTE *p=p_dst-3; hash[HASH(p)]=p; literals=2;}
+ }
+
+ /* Shift the control buffer so the next control bit is in bit 0. */
+ control>>=1;
+#if 1
+ if (p_dst > p_dst_post)
+ {
+ /* Shit: we tried to decompress corrupt data */
+ *p_dst_len = 0;
+ return;
+ }
+#endif
+ } /* End unrolled inner loop. */
+
+ } /* End of outer loop */
+
+ /* Write the length of the decompressed data before returning. */
+ *p_dst_len=p_dst-p_dst_first;
+}
+
+/******************************************************************************/
+/* End of LZRW3.C */
+/******************************************************************************/
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