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Add LZRW headers
2016-04-02 13:49:00 +00:00
//#pragma cplusplus off
/******************************************************************************/
/* */
/* LZRW3-A.C */
/* */
/******************************************************************************/
/* */
/* Author : Ross Williams. */
/* Date : 15-Jul-1991. */
/* Release : 1. */
/* */
/******************************************************************************/
/* */
/* This file contains an implementation of the LZRW3-A data compression */
/* algorithm in the C programming language. */
/* */
/* The LZRW3-A algorithm has the following features: */
/* */
/* 1 Requires only 16K of memory (for both compression and decompression). */
/* 2 The compressor runs about two times faster than Unix compress's. */
/* 3 The decompressor runs about three times faster than Unix compress's. */
/* 4 Yields a few percent better compression than Unix compress for */
/* most files. */
/* 5 Allows you to dial up extra compression at a speed cost in the */
/* compressor. The speed of the decompressor is not affected. */
/* 6 Algorithm is deterministic. */
/* 7 Algorithm is free of patent problems. The algorithm has not been */
/* patented (nor will it be) and is of the LZ77 class which is fairly */
/* clear of patents. */
/* 8 This implementation in C is in the public domain. */
/* */
/* (Timing tests for the speed comparison were performed on a Pyramid 9820.) */
/* */
/* LZRW3-A is LZRW3 with a deepened hash table. This simple change yields */
/* about a 6% (absolute) improvement in compression. */
/* */
/* 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 : Mon 15-Jul-1991 05:29PM | */
/* | Timing accuracy : One part in 100 | */
/* | Context length : 262144 bytes (= 256.0000K) | */
/* | Test suite : Calgary Corpus Suite | */
/* | Files in suite : 14 | */
/* | Algorithm : LZRW3-A | */
/* | 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 49044 44.1 3.53 8.47 31.19 | */
/* | us:Book1.D 768771 3 420464 54.7 4.38 7.27 30.07 | */
/* | us:Book2.D 610856 3 277955 45.5 3.64 8.51 33.40 | */
/* | rpus:Geo.D 102400 1 84218 82.2 6.58 4.23 15.04 | */
/* | pus:News.D 377109 2 192880 51.1 4.09 7.08 25.89 | */
/* | pus:Obj1.D 21504 1 12651 58.8 4.71 5.23 17.44 | */
/* | pus:Obj2.D 246814 1 108044 43.8 3.50 8.01 28.11 | */
/* | s:Paper1.D 53161 1 24526 46.1 3.69 8.11 30.24 | */
/* | s:Paper2.D 82199 1 39483 48.0 3.84 8.11 32.04 | */
/* | rpus:Pic.D 513216 2 111622 21.7 1.74 10.64 49.31 | */
/* | us:Progc.D 39611 1 17923 45.2 3.62 8.06 29.01 | */
/* | us:Progl.D 71646 1 24362 34.0 2.72 10.74 39.51 | */
/* | us:Progp.D 49379 1 16805 34.0 2.72 10.64 37.58 | */
/* | us:Trans.D 93695 1 30296 32.3 2.59 11.02 38.06 | */
/* +----------------------------------------------------------------+ */
/* | Average 224401 1 100733 45.8 3.67 8.29 31.21 | */
/* +----------------------------------------------------------------+ */
/* */
/******************************************************************************/
/* INCLUDE FILES */
/* ============= */
#include "port.h" /* Defines symbols for the non portable stuff. */
#include "compress.h" /* Defines single exported function "compress". */
//#include "fast_copy.h" /* Fast memory copy routine. */
/******************************************************************************/
/* 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-A uses the same amount of memory during compression and */
/* decompression. For more information on this structure see "compress.h". */
/* The alignment fudge below really only needs to be 4 (but I play it safe!). */
/* The id looks non-random, but it really was generated by coin tossing! */
#define U(X) ((ULONG) X)
#define SIZE_P_BYTE (U(sizeof(UBYTE *)))
#define ALIGNMENT_FUDGE (U(16))
#define MEM_REQ ( U(4096)*(SIZE_P_BYTE) + ALIGNMENT_FUDGE )
static compress_identity identity =
{
U(0x01B90B91), /* Algorithm identification number. */
MEM_REQ, /* Working memory (bytes) required. */
"LZRW3-A", /* Name of algorithm. */
"1.0 (safe)", /* Version number of algorithm. */
"15-Jul-1990", /* Date of algorithm. */
"Public Domain", /* Copyright notice. */
"Ross N. Williams", /* Author of algorithm. */
"Renaissance Software", /* Affiliation of author. */
"Public Domain" /* Vendor of algorithm. */
};
int compress_compress (UBYTE *,UBYTE *,ULONG,ULONG,UBYTE *,ULONG *);
int compress_decompress(UBYTE *,UBYTE *,ULONG,ULONG,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 int xcompress(
UWORD action, /* Action to be performed. */
UBYTE *wrk_mem, /* Address of working memory we can use. */
UBYTE *src_adr, /* Address of input data. */
ULONG src_len, /* Length of input data. */
ULONG dst_max, /* Maximum length of output buffer. */
UBYTE *dst_adr, /* Address to put output data. */
ULONG *p_dst_len) /* Address of longword for length of output data. */
{
switch (action)
{
case COMPRESS_ACTION_IDENTITY:
if (dst_max && (dst_max < sizeof(ULONG)))
return -1; /* Overflow */
*p_dst_len=(ULONG) &identity;
return 0;
break;
case COMPRESS_ACTION_COMPRESS:
return compress_compress
(wrk_mem,src_adr,src_len,dst_max,dst_adr,p_dst_len);
break;
case COMPRESS_ACTION_DECOMPRESS:
return compress_decompress
(wrk_mem,src_adr,src_len,dst_max,dst_adr,p_dst_len);
break;
}
return -1; /* Invalid selector */
}
/******************************************************************************/
/* */
/* BRIEF DESCRIPTION OF THE LZRW3-A ALGORITHM */
/* ========================================== */
/* Note: Before attempting to understand this algorithm, you should first */
/* understand the LZRW3 algorithm from which this algorithm is derived. */
/* */
/* The LZRW3-A algorithm is identical to the LZRW3 algorithm except that the */
/* hash table has been "deepened". The LZRW3 algorithm has a hash table of */
/* 4096 pointers which point to strings in the buffer. LZRW3-A generalizes */
/* this to 4096/(2^n) partitions each of which contains (2^n) pointers. */
/* In LZRW3-A, the hash function hashes to a partition number. */
/* */
/* During the processing of each phrase, LZRW3 overwrites the pointer in the */
/* position selected by the hash function. LZRW3-A overwrites one of the */
/* pointers in the partition that was selected by the hash function. */
/* */
/* When searching for a match, LZRW3-A matches against all (2^n) strings */
/* pointed to by the pointers in the target partition. */
/* */
/* Deep hash tables were used in early versions of LZRW1 in late 1989, but */
/* were discarded in an effort to increase speed (which was the primary */
/* requirement for LZRW1). They were revived for use in LZRW3-A in order to */
/* produce an algorithm with compression performance competitive with Unix */
/* compress. */
/* */
/* Until 14-Jul-1991, deep hash tables used in prototype LZRW* algorithms */
/* used a queue discipline within each partition. Upon the arrival of a new */
/* pointer, the pointers in the partition would be block copied back one */
/* position (with the oldest pointer being overwritten) and the new pointer */
/* being inserted in the space at the front (the youngest position). */
/* This meant that pointers to the (2^n) most recent phrases corresponding to */
/* each hash was kept. The only flaw in this system was the time-consuming */
/* block copy operation which was cheap for shallow tables but expensive for */
/* deep tables. */
/* */
/* The traditional solution to ring buffer block copy problems is to maintain */
/* a cyclic counter which points to the "head" of the queue. However, this */
/* would have required one counter to be stored for each partition and would */
/* have been slightly messy. After some thought (on 14-Jul-1991) a better */
/* solution was found. Instead of maintaining a counter for each partition, */
/* LZRW3-A maintains a single counter for all partitions! This counter is */
/* maintained in both the compressor and decompressor and means that the */
/* algorithm (effectively) overwrites a RANDOM element of the partition to be */
/* updated. The result was to increase the speed of the compressor and */
/* decompressor, to make the decompressor's speed independent from whatever */
/* depth was selected, and to impair compression by less than 1% absolute. */
/* */
/* Setting the depth is a speed/compression tradeoff. The table below gives */
/* the tradeoff observed for a typical 50K text file on a Mac-SE. */
/* Note: %Rem=Percentage Remaining (after compression). */
/* */
/* Depth %Rem CmpK/s DecK/s */
/* 1 45.2 14.77 32.24 */
/* 2 42.6 12.12 31.26 */
/* 4 40.9 10.28 31.91 */
/* 8 40.0 7.81 32.36 */
/* 16 39.5 5.30 32.47 */
/* 32 39.0 3.23 32.59 */
/* */
/* I have chosen a depth of 8 as the "default" depth for LZRW3-A. If you use */
/* a depth different to this (e.g. 4), you should use the name LZRW3-A(4) to */
/* indicate that a different depth is being used. LZRW3-A(8) is an acceptable */
/* longhand for LZRW3-A. */
/* */
/* To change the depth, search for "HERE IT IS" in the rest of this file. */
/* */
/* +---+ */
/* |___|4095 */
/* |===| */
/* +---------------------*_|<---+ /----+---\ */
/* | |___| +---|Hash | */
/* | 512 partitions |___| |Function| */
/* | of 8 pointers |===| \--------/ */
/* | each (or any |___|0 ^ */
/* | a*b=4096) +---+ | */
/* | Hash +-----+ */
/* | Table | */
/* | --- */
/* v ^^^ */
/* +-------------------------------------|----------------+ */
/* |||||||||||||||||||||||||||||||||||||||||||||||||||||||| */
/* +-------------------------------------|----------------+ */
/* | |1......18| | */
/* |<------- Lempel=History ------------>|<--Ziv-->| | */
/* | (=bytes already processed) |<-Still to go-->| */
/* |<-------------------- INPUT BLOCK ------------------->| */
/* */
/* */
/******************************************************************************/
/* */
/* 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. */
/* */
/******************************************************************************/
/* When I first started to get concerned about the portability of my C code, */
/* I switched over to using only macro defined types UBYTE, UWORD, ULONG and */
/* one or two others. While, these are useful for most purposes, they impair */
/* efficiency as, if I have a variable whose range will be [0,1000], I will */
/* declare it as a UWORD. This will translate into (say) "short int" and */
/* hence may be less efficient than just an "int" which represents the */
/* natural size of the machine. Before releasing LZRW3-A, I realized this */
/* mistake. Unfortunately, I can't access the ftp archive with my portability */
/* header in it in time for this algorithm's release and so I am including an */
/* extra definition. The definition UCARD stands for an unsigned (cardinal) */
/* type that can hold values in the range [0,32767]. This is within the ANSI */
/* range of a standard int or unsigned. No assumption about overflow of this */
/* type is made in the code (i.e. all usages are within range and I do not */
/* use the value -1 to detect the end of loops.). */
/* You can use either "unsigned" or just "int" here depending on which is */
/* more efficient in your environment (both the same probably). */
#define UCARD unsigned
/* 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)+3)&~3)
/* 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)
/* This constant defines the number of pointers in the hash table. The number */
/* of partitions multiplied by the number of pointers in each partition must */
/* multiply out to this value of 4096. In LZRW1, LZRW1-A, and LZRW2, this */
/* table length value can be changed. However, in LZRW3-A (and LZRW3), the */
/* table length cannot be changed because it is connected directly to the */
/* coding scheme which is hardwired (the table index of a single pointer is */
/* transmitted in the 12-bit index field). So don't change this constant! */
#define HASH_TABLE_LENGTH (4096)
/* HERE IT IS: THE PLACE TO CHANGE THE HASH TABLE DEPTH! */
/* The following definition is the log_2 of the depth of the hash table. This */
/* constant can be in the range [0,1,2,3,...,12]. Increasing the depth */
/* increases compression at the expense of speed. However, you are not likely */
/* to see much of a compression improvement (e.g. not more than 0.5%) above a */
/* value of 6 and the algorithm will start to get very slow. See the table in */
/* the earlier comments block for an idea of the trade-off involved. */
/* Note: The parentheses are to avoid macro substitution funnies. */
/* Note: The LZRW3-A default is a value of (3). */
/* Note: If you end up choosing a value of 0, you should use LZRW3 instead. */
/* Note: Changing the value of HASH_TABLE_DEPTH_BITS is the ONLY thing you */
/* have to do to change the depth, so go ahead and recompile now! */
/* Note: I have tested LZRW3-A for DEPTH_BITS=0,1,2,3,4 and a few other */
/* values. However, I have not tested it for 12 as I can't wait that long! */
#define HASH_TABLE_DEPTH_BITS (3) /* Must be in range [0,12]. */
/* The following definitions are all self-explanatory and follow from the */
/* definition of HASH_TABLE_DEPTH_BITS and the hardwired requirement that the */
/* hash table contain exactly 4096 pointers. */
#define PARTITION_LENGTH_BITS (12-HASH_TABLE_DEPTH_BITS)
#define PARTITION_LENGTH (1<<PARTITION_LENGTH_BITS)
#define HASH_TABLE_DEPTH (1<<HASH_TABLE_DEPTH_BITS )
#define HASH_MASK (PARTITION_LENGTH-1)
#define DEPTH_MASK (HASH_TABLE_DEPTH-1)
/* LZRW3-A, 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 LZRW3, 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")
/* The following macro accepts a pointer PTR to three consecutive bytes in */
/* memory and hashes them into an integer that is a hash table index that */
/* points to the zeroth (first) element of a partition. Thus, the hash */
/* function really hashes to a partition number but, for convenience, */
/* multiplies it up to yield a hash table index. From all this, we see that */
/* the resultant number is in the range [0,HASH_TABLE_LENGTH-1] and is a */
/* multiple of HASH_TABLE_DEPTH. */
/* A macro is used, because in LZRW3-A we have to hash more than once. */
#define HASH(PTR) \
( \
(((40543*(((*(PTR))<<8)^((*((PTR)+1))<<4)^(*((PTR)+2))))>>4) & HASH_MASK) \
<< HASH_TABLE_DEPTH_BITS \
)
/* Another operation that is performed more than once is the updating of the */
/* hash table. Here two macros are defined to simplify update operations. */
/* Updating consists of identifying and overwriting a pointer in a partition */
/* with a newer pointer and then updating the global cycle value. */
/* These macros accept the new pointer (NEWPTR) and either a pointer to */
/* (P_BASE) or the index of (I_BASE) the zeroth (first, or base) pointer in */
/* the partition that is to be updated. The macros use the 'cycle' variable */
/* to locate and overwrite a pointer and then update the cycle value. */
/* Note: Hardcoding 'cycle' in this macro is naughty (it should really be a */
/* macro parameter), but I have done so because it neatens up the code. */
#define UPDATE_P(P_BASE,NEWPTR) \
{(P_BASE)[cycle++]=(NEWPTR); cycle&=DEPTH_MASK;}
#define UPDATE_I(I_BASE,NEWPTR) \
{hash[(I_BASE)+cycle++]=(NEWPTR); cycle&=DEPTH_MASK;}
/* This constant supplies a legal (in-range) hash table index for use when */
/* a legal-but-don't-care index is required. */
#define ANY_HASH_INDEX (0)
/******************************************************************************/
int compress_compress
(
/* 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. */
/* Input : Maximum length of output buffer. */
/* 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,
ULONG dst_max,
UBYTE *p_dst_first,
ULONG *p_dst_len)
{
/* p_src and p_dst step through the source and destination blocks. */
UBYTE *p_src = p_src_first;
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;
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 partition (i.e. the zero'th (first) element of the partition) */
/* corresponding to the youngest literal. p_h2 points to the partition */
/* corresponding to the second youngest literal. */
/* The value zero denotes an "empty" buffer value with p_h1=0 => p_h2=0. */
UBYTE **p_h1=0;
UBYTE **p_h2=0;
/* The following variable holds the current 'cycle' value. This value cycles */
/* through the range [0,HASH_TABLE_DEPTH-1], being incremented every time */
/* the hash table is updated. The value gives the within-partition number of */
/* the next pointer to be overwritten. The decompressor maintains a cycle */
/* value in synchrony. */
UCARD cycle=0;
/* Validate the output buffer size before starting any compression. */
if (dst_max && (dst_max < src_len+FLAG_BYTES))
goto dst_overrun;
/* 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;
{UCARD 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. */
/* These variables should really be declared "register", but I am worried */
/* about the possibility that extra register declarations will tempt stupid */
/* compilers to allocate all registers before they get to the innermostloop. */
{UCARD 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. */
UBYTE *p_ziv; /* Points to first byte of current Ziv. */
UCARD unroll; /* Loop counter for unrolled inner loop. */
UCARD index; /* Index of current partition. */
UBYTE **p_h0; /* Pointer to current partition. */
register UCARD d; /* Depth looping variable. */
register UCARD bestlen; /* Holds the best length seen so far. */
register UCARD bestpos; /* Holds number of best pointer seen so far. */
/* 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
{p_h0=&hash[ANY_HASH_INDEX]; /* Avoid undefined pointer. */
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:
p_ziv=p_src;
/* To process the next phrase, we hash the next three bytes to obtain */
/* an index to the zeroth (first) pointer in a target partition. We */
/* get the pointer. */
index=HASH(p_src);
p_h0=&hash[index];
/* This next part runs through the pointers in the partition matching */
/* the bytes they point to in the Lempel with the bytes in the Ziv. */
/* The length (bestlen) and within-partition pointer number (bestpos) */
/* of the longest match so far is maintained and is the output of this */
/* segment of code. The s[bestlen]==... is an optimization only. */
bestlen=0;
bestpos=0;
for (d=0;d<HASH_TABLE_DEPTH;d++)
{
register UBYTE *s=p_src;
register UBYTE *p=p_h0[d];
register UCARD len;
if (s[bestlen] == p[bestlen])
{
#define PS *p++!=*s++
PS || PS || PS || PS || PS || PS || PS || PS || PS ||
PS || PS || PS || PS || PS || PS || PS || PS || PS || s++;
len=s-p_src-1;
if (len>bestlen)
{
bestpos=d;
bestlen=len;
}
}
}
/* The length of the longest match determines whether we code a */
/* literal item or a copy item. */
if (bestlen<3)
{
/* Literal. */
/* Code the literal byte as itself and a zero control bit. */
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)
{UPDATE_P(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 */
/* To code a copy item, we construct a hash table index of the */
/* winning pointer (index+=bestpos) and code it and the best length */
/* into a 2 byte code word. Bump up p_src. */
index+=bestpos;
*p_dst++=((index&0xF00)>>4)|(bestlen-3);
*p_dst++=index&0xFF;
p_src+=bestlen;
/* 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)
{UPDATE_P(p_h2,p_ziv-2); p_h2=0;}
UPDATE_P(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. */
UPDATE_P(p_h0,p_ziv);
}
control>>=1;
/* This loop is all set up for a decrement and jump instruction! */
end_unrolled_loop: if (--unroll) goto begin_unrolled_loop;
/* 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 0;
/* 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:
*p_dst_first=FLAG_COPY;
fast_copy(p_src_first,p_dst_first+FLAG_BYTES,src_len);
*p_dst_len=src_len+FLAG_BYTES;
return 0;
/* Jump here if the destination buffer is insufficient to hold the output */
/* data. We return -1 to indicate an error and set the output length to 0. */
dst_overrun:
*p_dst_len = 0;
return -1;
}
/******************************************************************************/
int compress_decompress
(
/* 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 : Maximum length of output buffer. */
/* 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,
ULONG src_len,
ULONG dst_max,
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;
/* 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 UCARD literals=0;
/* The following variable holds the current 'cycle' value. This value cycles */
/* through the range [0,HASH_TABLE_DEPTH-1], being incremented every time */
/* the hash table is updated. The value give the within-partition number of */
/* the next pointer to be overwritten. The compressor maintains a cycle */
/* value in synchrony. */
UCARD cycle=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 (*p_src_first==FLAG_COPY)
{
/* Check for destination buffer for overflow before writing data. */
if (dst_max && (dst_max < src_len-FLAG_BYTES))
goto dst_overrun;
fast_copy(p_src_first+FLAG_BYTES,p_dst_first,src_len-FLAG_BYTES);
*p_dst_len=src_len-FLAG_BYTES;
return 0;
}
/* Initialize all elements of the hash table to point to a constant string. */
/* Use of an unrolled loop speeds this up considerably. */
/* The comment about register declarations above similar code in the */
/* compressor applies here too. */
{UCARD 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 UCARD 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 UCARD lenmt; /* Length of copy item minus three. */
register UBYTE *p_ziv=p_dst; /* Pointer to start of current Ziv. */
register UCARD index; /* Index of hash table copy pointer. */
/* Read and dismantle the copy word. Work out from where to copy. */
lenmt=*p_src++;
index=((lenmt&0xF0)<<4)|*p_src++;
p=hash[index];
lenmt&=0xF;
/* Check for destination buffer for overflow before writing data. */
if (dst_max && (dst_max < p_dst-p_dst_first+lenmt+3))
goto dst_overrun;
/* 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;;
UPDATE_I(HASH(r),r);
if (literals==2)
{r++; UPDATE_I(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!!! */
UPDATE_I(index&(~DEPTH_MASK),p_ziv);
}
else
{
/* Literal item. */
/* Check for destination buffer for overflow before writing data. */
if (dst_max && (dst_max < p_dst-p_dst_first+1))
goto dst_overrun;
/* 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;
UPDATE_I(HASH(p),p); literals=2;}
}
/* Shift the control buffer so the next control bit is in bit 0. */
control>>=1;
} /* 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;
return 0;
/* Jump here if the destination buffer is insufficient to hold the output */
/* data. We return -1 to indicate an error and set the output length to 0. */
dst_overrun:
*p_dst_len = 0;
return -1;
}
/******************************************************************************/
/* End of LZRW3-A.C */
/******************************************************************************/
Reference in New Issue Copy Permalink