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6b516f5951
search lists was broken in such a way that only the most recent instance of a given hash code would ever be searched, thus possibly missing longer matches further back. Fixing this gave 5 to 10% compression improvement on some text test cases. Additional small tweaks to improve speed of inner loops a little bit. There is no compatibility issue created by this change, since the compressed data format and decompression algorithm don't change.
904 lines
24 KiB
C
904 lines
24 KiB
C
/* ----------
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* pg_lzcompress.c -
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*
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* $Header: /cvsroot/pgsql/src/backend/utils/adt/pg_lzcompress.c,v 1.14 2001/11/17 06:09:30 tgl Exp $
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*
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* This is an implementation of LZ compression for PostgreSQL.
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* It uses a simple history table and generates 2-3 byte tags
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* capable of backward copy information for 3-273 bytes with
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* an offset of max. 4095.
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*
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* Entry routines:
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*
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* int
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* pglz_compress(char *source, int slen, PGLZ_Header *dest,
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* PGLZ_Strategy *strategy);
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*
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* source is the input data to be compressed.
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*
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* slen is the length of the input data.
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*
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* dest is the output area for the compressed result.
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* It must be big enough to hold the worst case of
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* compression failure and can be computed by the
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* macro PGLZ_MAX_OUTPUT(slen). Don't be surprised,
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* it is larger than the input data size.
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*
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* strategy is a pointer to some information controlling
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* the compression algorithm. If NULL, the compiled
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* in default strategy is used.
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*
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* The return value is the size of bytes written to buff.
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*
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* int
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* pglz_decompress(PGLZ_Header *source, char *dest)
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*
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* source is the compressed input.
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*
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* dest is the area where the uncompressed data will be
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* written to. It is the callers responsibility to
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* provide enough space. The required amount can be
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* obtained with the macro PGLZ_RAW_SIZE(source).
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*
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* The data is written to buff exactly as it was handed
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* to pglz_compress(). No terminating zero byte is added.
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*
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* The return value is the size of bytes written to buff.
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* Obviously the same as PGLZ_RAW_SIZE() returns.
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*
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* The decompression algorithm and internal data format:
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*
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* PGLZ_Header is defined as
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*
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* typedef struct PGLZ_Header {
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* int32 varsize;
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* int32 rawsize;
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* }
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*
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* The header is followed by the compressed data itself.
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*
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* The data representation is easiest explained by describing
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* the process of decompression.
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*
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* If varsize == rawsize + sizeof(PGLZ_Header), then the data
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* is stored uncompressed as plain bytes. Thus, the decompressor
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* simply copies rawsize bytes from the location after the
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* header to the destination.
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*
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* Otherwise the first byte after the header tells what to do
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* the next 8 times. We call this the control byte.
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*
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* An unset bit in the control byte means, that one uncompressed
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* byte follows, which is copied from input to output.
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*
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* A set bit in the control byte means, that a tag of 2-3 bytes
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* follows. A tag contains information to copy some bytes, that
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* are already in the output buffer, to the current location in
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* the output. Let's call the three tag bytes T1, T2 and T3. The
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* position of the data to copy is coded as an offset from the
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* actual output position.
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*
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* The offset is in the upper nibble of T1 and in T2.
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* The length is in the lower nibble of T1.
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*
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* So the 16 bits of a 2 byte tag are coded as
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*
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* 7---T1--0 7---T2--0
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* OOOO LLLL OOOO OOOO
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*
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* This limits the offset to 1-4095 (12 bits) and the length
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* to 3-18 (4 bits) because 3 is allways added to it. To emit
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* a tag of 2 bytes with a length of 2 only saves one control
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* bit. But we lose one byte in the possible length of a tag.
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*
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* In the actual implementation, the 2 byte tag's length is
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* limited to 3-17, because the value 0xF in the length nibble
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* has special meaning. It means, that the next following
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* byte (T3) has to be added to the length value of 18. That
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* makes total limits of 1-4095 for offset and 3-273 for length.
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*
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* Now that we have successfully decoded a tag. We simply copy
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* the output that occured <offset> bytes back to the current
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* output location in the specified <length>. Thus, a
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* sequence of 200 spaces (think about bpchar fields) could be
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* coded in 4 bytes. One literal space and a three byte tag to
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* copy 199 bytes with a -1 offset. Whow - that's a compression
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* rate of 98%! Well, the implementation needs to save the
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* original data size too, so we need another 4 bytes for it
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* and end up with a total compression rate of 96%, what's still
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* worth a Whow.
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*
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* The compression algorithm
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*
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* The following uses numbers used in the default strategy.
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*
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* The compressor works best for attributes of a size between
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* 1K and 1M. For smaller items there's not that much chance of
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* redundancy in the character sequence (except for large areas
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* of identical bytes like trailing spaces) and for bigger ones
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* our 4K maximum look-back distance is too small.
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*
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* The compressor creates a table for 8192 lists of positions.
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* For each input position (except the last 3), a hash key is
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* built from the 4 next input bytes and the position remembered
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* in the appropriate list. Thus, the table points to linked
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* lists of likely to be at least in the first 4 characters
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* matching strings. This is done on the fly while the input
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* is compressed into the output area. Table entries are only
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* kept for the last 4096 input positions, since we cannot use
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* back-pointers larger than that anyway.
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*
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* For each byte in the input, it's hash key (built from this
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* byte and the next 3) is used to find the appropriate list
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* in the table. The lists remember the positions of all bytes
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* that had the same hash key in the past in increasing backward
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* offset order. Now for all entries in the used lists, the
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* match length is computed by comparing the characters from the
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* entries position with the characters from the actual input
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* position.
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*
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* The compressor starts with a so called "good_match" of 128.
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* It is a "prefer speed against compression ratio" optimizer.
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* So if the first entry looked at already has 128 or more
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* matching characters, the lookup stops and that position is
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* used for the next tag in the output.
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*
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* For each subsequent entry in the history list, the "good_match"
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* is lowered by 10%. So the compressor will be more happy with
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* short matches the farer it has to go back in the history.
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* Another "speed against ratio" preference characteristic of
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* the algorithm.
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*
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* Thus there are 3 stop conditions for the lookup of matches:
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*
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* - a match >= good_match is found
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* - there are no more history entries to look at
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* - the next history entry is already too far back
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* to be coded into a tag.
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*
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* Finally the match algorithm checks that at least a match
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* of 3 or more bytes has been found, because thats the smallest
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* amount of copy information to code into a tag. If so, a tag
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* is omitted and all the input bytes covered by that are just
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* scanned for the history add's, otherwise a literal character
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* is omitted and only his history entry added.
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*
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* Acknowledgements:
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*
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* Many thanks to Adisak Pochanayon, who's article about SLZ
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* inspired me to write the PostgreSQL compression this way.
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*
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* Jan Wieck
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* ----------
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*/
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#include "postgres.h"
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#include <unistd.h>
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#include <fcntl.h>
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#include <errno.h>
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#include "utils/pg_lzcompress.h"
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/* ----------
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* Local definitions
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* ----------
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*/
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#define PGLZ_HISTORY_LISTS 8192 /* must be power of 2 */
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#define PGLZ_HISTORY_MASK (PGLZ_HISTORY_LISTS - 1)
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#define PGLZ_HISTORY_SIZE 4096
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#define PGLZ_MAX_MATCH 273
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/* ----------
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* PGLZ_HistEntry -
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*
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* Linked list for the backward history lookup
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*
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* All the entries sharing a hash key are linked in a doubly linked list.
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* This makes it easy to remove an entry when it's time to recycle it
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* (because it's more than 4K positions old).
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* ----------
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*/
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typedef struct PGLZ_HistEntry
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{
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struct PGLZ_HistEntry *next; /* links for my hash key's list */
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struct PGLZ_HistEntry *prev;
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int hindex; /* my current hash key */
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char *pos; /* my input position */
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} PGLZ_HistEntry;
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/* ----------
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* The provided standard strategies
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* ----------
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*/
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static PGLZ_Strategy strategy_default_data = {
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256, /* Data chunks smaller 256 bytes are not
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* compressed */
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6144, /* Data chunks greater equal 6K force
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* compression */
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/* except compressed result is greater uncompressed data */
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20, /* Compression rates below 20% mean
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* fallback to uncompressed */
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/* storage except compression is forced by previous parameter */
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128, /* Stop history lookup if a match of 128
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* bytes is found */
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10 /* Lower good match size by 10% at every
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* lookup loop iteration. */
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};
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PGLZ_Strategy *PGLZ_strategy_default = &strategy_default_data;
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static PGLZ_Strategy strategy_allways_data = {
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0, /* Chunks of any size are compressed */
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0, /* */
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0, /* We want to save at least one single
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* byte */
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128, /* Stop history lookup if a match of 128
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* bytes is found */
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6 /* Look harder for a good match. */
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};
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PGLZ_Strategy *PGLZ_strategy_allways = &strategy_allways_data;
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static PGLZ_Strategy strategy_never_data = {
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0, /* */
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0, /* */
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0, /* */
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0, /* Zero indicates "store uncompressed
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* allways" */
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0 /* */
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};
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PGLZ_Strategy *PGLZ_strategy_never = &strategy_never_data;
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/* ----------
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* Statically allocated work arrays for history
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* ----------
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*/
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static PGLZ_HistEntry *hist_start[PGLZ_HISTORY_LISTS];
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static PGLZ_HistEntry hist_entries[PGLZ_HISTORY_SIZE];
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/* ----------
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* pglz_hist_idx -
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*
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* Computes the history table slot for the lookup by the next 4
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* characters in the input.
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*
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* NB: because we use the next 4 characters, we are not guaranteed to
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* find 3-character matches; they very possibly will be in the wrong
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* hash list. This seems an acceptable tradeoff for spreading out the
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* hash keys more.
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* ----------
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*/
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#define pglz_hist_idx(_s,_e) ( \
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((((_e) - (_s)) < 4) ? (int) (_s)[0] : \
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(((_s)[0] << 9) ^ ((_s)[1] << 6) ^ \
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((_s)[2] << 3) ^ (_s)[3])) & (PGLZ_HISTORY_MASK) \
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)
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/* ----------
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* pglz_hist_add -
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*
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* Adds a new entry to the history table.
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*
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* If _recycle is true, then we are recycling a previously used entry,
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* and must first delink it from its old hashcode's linked list.
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*
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* NOTE: beware of multiple evaluations of macro's arguments, and note that
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* _hn and _recycle are modified in the macro.
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* ----------
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*/
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#define pglz_hist_add(_hs,_he,_hn,_recycle,_s,_e) \
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do { \
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int __hindex = pglz_hist_idx((_s),(_e)); \
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PGLZ_HistEntry **__myhsp = &(_hs)[__hindex]; \
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PGLZ_HistEntry *__myhe = &(_he)[_hn]; \
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if (_recycle) { \
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if (__myhe->prev == NULL) \
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(_hs)[__myhe->hindex] = __myhe->next; \
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else \
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__myhe->prev->next = __myhe->next; \
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if (__myhe->next != NULL) \
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__myhe->next->prev = __myhe->prev; \
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} \
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__myhe->next = *__myhsp; \
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__myhe->prev = NULL; \
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__myhe->hindex = __hindex; \
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__myhe->pos = (_s); \
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if (*__myhsp != NULL) \
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(*__myhsp)->prev = __myhe; \
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*__myhsp = __myhe; \
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if (++(_hn) >= PGLZ_HISTORY_SIZE) { \
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(_hn) = 0; \
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(_recycle) = true; \
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} \
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} while (0)
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/* ----------
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* pglz_out_ctrl -
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*
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* Outputs the last and allocates a new control byte if needed.
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* ----------
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*/
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#define pglz_out_ctrl(__ctrlp,__ctrlb,__ctrl,__buf) \
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do { \
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if ((__ctrl & 0xff) == 0) \
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{ \
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*__ctrlp = __ctrlb; \
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__ctrlp = __buf++; \
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__ctrlb = 0; \
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__ctrl = 1; \
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} \
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} while (0)
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/* ----------
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* pglz_out_literal -
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*
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* Outputs a literal byte to the destination buffer including the
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* appropriate control bit.
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* ----------
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*/
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#define pglz_out_literal(_ctrlp,_ctrlb,_ctrl,_buf,_byte) \
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do { \
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pglz_out_ctrl(_ctrlp,_ctrlb,_ctrl,_buf); \
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*_buf++ = (unsigned char)(_byte); \
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_ctrl <<= 1; \
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} while (0)
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/* ----------
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* pglz_out_tag -
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*
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* Outputs a backward reference tag of 2-4 bytes (depending on
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* offset and length) to the destination buffer including the
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* appropriate control bit.
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* ----------
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*/
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#define pglz_out_tag(_ctrlp,_ctrlb,_ctrl,_buf,_len,_off) \
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do { \
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pglz_out_ctrl(_ctrlp,_ctrlb,_ctrl,_buf); \
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_ctrlb |= _ctrl; \
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_ctrl <<= 1; \
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if (_len > 17) \
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{ \
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_buf[0] = (unsigned char)((((_off) & 0xf00) >> 4) | 0x0f); \
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_buf[1] = (unsigned char)((_off & 0xff)); \
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_buf[2] = (unsigned char)((_len) - 18); \
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_buf += 3; \
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} else { \
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_buf[0] = (unsigned char)((((_off) & 0xf00) >> 4) | (_len - 3)); \
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_buf[1] = (unsigned char)((_off) & 0xff); \
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_buf += 2; \
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} \
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} while (0)
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/* ----------
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* pglz_find_match -
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*
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* Lookup the history table if the actual input stream matches
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* another sequence of characters, starting somewhere earlier
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* in the input buffer.
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* ----------
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*/
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static inline int
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pglz_find_match(PGLZ_HistEntry **hstart, char *input, char *end,
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int *lenp, int *offp, int good_match, int good_drop)
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{
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PGLZ_HistEntry *hent;
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int32 len = 0;
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int32 off = 0;
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/*
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* Traverse the linked history list until a good enough match is
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* found.
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*/
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hent = hstart[pglz_hist_idx(input, end)];
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while (hent)
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{
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char *ip = input;
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char *hp = hent->pos;
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int32 thisoff;
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int32 thislen;
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/*
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* Stop if the offset does not fit into our tag anymore.
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*/
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thisoff = ip - hp;
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if (thisoff >= 0x0fff)
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break;
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/*
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* Determine length of match. A better match must be larger than
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* the best so far. And if we already have a match of 16 or more
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* bytes, it's worth the call overhead to use memcmp() to check if
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* this match is equal for the same size. After that we must
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* fallback to character by character comparison to know the
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* exact position where the diff occured.
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*/
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thislen = 0;
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if (len >= 16)
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{
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if (memcmp(ip, hp, len) == 0)
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{
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thislen = len;
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ip += len;
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hp += len;
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while (ip < end && *ip == *hp && thislen < PGLZ_MAX_MATCH)
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{
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thislen++;
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ip++;
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hp++;
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}
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}
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}
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else
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{
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while (ip < end && *ip == *hp && thislen < PGLZ_MAX_MATCH)
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{
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thislen++;
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ip++;
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hp++;
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}
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}
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/*
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* Remember this match as the best (if it is)
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*/
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if (thislen > len)
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{
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len = thislen;
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off = thisoff;
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}
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/*
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* Advance to the next history entry
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*/
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hent = hent->next;
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/*
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* Be happy with lesser good matches the more entries we visited.
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* But no point in doing calculation if we're at end of list.
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*/
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if (hent)
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{
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if (len >= good_match)
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break;
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good_match -= (good_match * good_drop) / 100;
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}
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}
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/*
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* Return match information only if it results at least in one byte
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* reduction.
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*/
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if (len > 2)
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{
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*lenp = len;
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*offp = off;
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return 1;
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}
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return 0;
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}
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/* ----------
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* pglz_compress -
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*
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* Compresses source into dest using strategy.
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* ----------
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*/
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int
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pglz_compress(char *source, int32 slen, PGLZ_Header *dest, PGLZ_Strategy *strategy)
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{
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unsigned char *bp = ((unsigned char *) dest) + sizeof(PGLZ_Header);
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unsigned char *bstart = bp;
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int hist_next = 0;
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bool hist_recycle = false;
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char *dp = source;
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char *dend = source + slen;
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unsigned char ctrl_dummy = 0;
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unsigned char *ctrlp = &ctrl_dummy;
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unsigned char ctrlb = 0;
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unsigned char ctrl = 0;
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int32 match_len;
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int32 match_off;
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int32 good_match;
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int32 good_drop;
|
|
int32 do_compress = 1;
|
|
int32 result_size = -1;
|
|
int32 result_max;
|
|
int32 need_rate;
|
|
|
|
/*
|
|
* Our fallback strategy is the default.
|
|
*/
|
|
if (strategy == NULL)
|
|
strategy = PGLZ_strategy_default;
|
|
|
|
/*
|
|
* Save the original source size in the header.
|
|
*/
|
|
dest->rawsize = slen;
|
|
|
|
/*
|
|
* If the strategy forbids compression (at all or if source chunk too
|
|
* small), copy input to output without compression.
|
|
*/
|
|
if (strategy->match_size_good == 0)
|
|
{
|
|
memcpy(bstart, source, slen);
|
|
return (dest->varsize = slen + sizeof(PGLZ_Header));
|
|
}
|
|
else
|
|
{
|
|
if (slen < strategy->min_input_size)
|
|
{
|
|
memcpy(bstart, source, slen);
|
|
return (dest->varsize = slen + sizeof(PGLZ_Header));
|
|
}
|
|
}
|
|
|
|
/*
|
|
* Limit the match size to the maximum implementation allowed value
|
|
*/
|
|
if ((good_match = strategy->match_size_good) > PGLZ_MAX_MATCH)
|
|
good_match = PGLZ_MAX_MATCH;
|
|
if (good_match < 17)
|
|
good_match = 17;
|
|
|
|
if ((good_drop = strategy->match_size_drop) < 0)
|
|
good_drop = 0;
|
|
if (good_drop > 100)
|
|
good_drop = 100;
|
|
|
|
/*
|
|
* Initialize the history lists to empty. We do not need to zero
|
|
* the hist_entries[] array; its entries are initialized as they
|
|
* are used.
|
|
*/
|
|
memset((void *) hist_start, 0, sizeof(hist_start));
|
|
|
|
/*
|
|
* Compute the maximum result size allowed by the strategy. If the
|
|
* input size exceeds force_input_size, the max result size is the
|
|
* input size itself. Otherwise, it is the input size minus the
|
|
* minimum wanted compression rate.
|
|
*/
|
|
if (slen >= strategy->force_input_size)
|
|
result_max = slen;
|
|
else
|
|
{
|
|
need_rate = strategy->min_comp_rate;
|
|
if (need_rate < 0)
|
|
need_rate = 0;
|
|
else if (need_rate > 99)
|
|
need_rate = 99;
|
|
result_max = slen - ((slen * need_rate) / 100);
|
|
}
|
|
|
|
/*
|
|
* Compress the source directly into the output buffer.
|
|
*/
|
|
while (dp < dend)
|
|
{
|
|
/*
|
|
* If we already exceeded the maximum result size, set no
|
|
* compression flag and stop this. But don't check too often.
|
|
*/
|
|
if (bp - bstart >= result_max)
|
|
{
|
|
do_compress = 0;
|
|
break;
|
|
}
|
|
|
|
/*
|
|
* Try to find a match in the history
|
|
*/
|
|
if (pglz_find_match(hist_start, dp, dend, &match_len,
|
|
&match_off, good_match, good_drop))
|
|
{
|
|
/*
|
|
* Create the tag and add history entries for all matched
|
|
* characters.
|
|
*/
|
|
pglz_out_tag(ctrlp, ctrlb, ctrl, bp, match_len, match_off);
|
|
while (match_len--)
|
|
{
|
|
pglz_hist_add(hist_start, hist_entries,
|
|
hist_next, hist_recycle,
|
|
dp, dend);
|
|
dp++; /* Do not do this ++ in the line above! */
|
|
/* The macro would do it four times - Jan. */
|
|
}
|
|
}
|
|
else
|
|
{
|
|
/*
|
|
* No match found. Copy one literal byte.
|
|
*/
|
|
pglz_out_literal(ctrlp, ctrlb, ctrl, bp, *dp);
|
|
pglz_hist_add(hist_start, hist_entries,
|
|
hist_next, hist_recycle,
|
|
dp, dend);
|
|
dp++; /* Do not do this ++ in the line above! */
|
|
/* The macro would do it four times - Jan. */
|
|
}
|
|
}
|
|
|
|
/*
|
|
* If we are still in compressing mode, write out the last control
|
|
* byte and determine if the compression gained the rate requested by
|
|
* the strategy.
|
|
*/
|
|
if (do_compress)
|
|
{
|
|
*ctrlp = ctrlb;
|
|
|
|
result_size = bp - bstart;
|
|
if (result_size >= result_max)
|
|
do_compress = 0;
|
|
}
|
|
|
|
/*
|
|
* Done - if we successfully compressed and matched the strategy's
|
|
* constraints, return the compressed result. Otherwise copy the
|
|
* original source over it and return the original length.
|
|
*/
|
|
if (do_compress)
|
|
{
|
|
dest->varsize = result_size + sizeof(PGLZ_Header);
|
|
return VARATT_SIZE(dest);
|
|
}
|
|
else
|
|
{
|
|
memcpy(((char *) dest) + sizeof(PGLZ_Header), source, slen);
|
|
dest->varsize = slen + sizeof(PGLZ_Header);
|
|
return VARATT_SIZE(dest);
|
|
}
|
|
}
|
|
|
|
|
|
/* ----------
|
|
* pglz_decompress -
|
|
*
|
|
* Decompresses source into dest.
|
|
* ----------
|
|
*/
|
|
int
|
|
pglz_decompress(PGLZ_Header *source, char *dest)
|
|
{
|
|
unsigned char *dp;
|
|
unsigned char *dend;
|
|
unsigned char *bp;
|
|
unsigned char ctrl;
|
|
int32 ctrlc;
|
|
int32 len;
|
|
int32 off;
|
|
|
|
dp = ((unsigned char *) source) + sizeof(PGLZ_Header);
|
|
dend = ((unsigned char *) source) + VARATT_SIZE(source);
|
|
bp = (unsigned char *) dest;
|
|
|
|
if (VARATT_SIZE(source) == source->rawsize + sizeof(PGLZ_Header))
|
|
{
|
|
memcpy(dest, dp, source->rawsize);
|
|
return source->rawsize;
|
|
}
|
|
|
|
while (dp < dend)
|
|
{
|
|
/*
|
|
* Read one control byte and process the next 8 items.
|
|
*/
|
|
ctrl = *dp++;
|
|
for (ctrlc = 0; ctrlc < 8 && dp < dend; ctrlc++)
|
|
{
|
|
if (ctrl & 1)
|
|
{
|
|
/*
|
|
* Otherwise it contains the match length minus 3 and the
|
|
* upper 4 bits of the offset. The next following byte
|
|
* contains the lower 8 bits of the offset. If the length
|
|
* is coded as 18, another extension tag byte tells how
|
|
* much longer the match really was (0-255).
|
|
*/
|
|
len = (dp[0] & 0x0f) + 3;
|
|
off = ((dp[0] & 0xf0) << 4) | dp[1];
|
|
dp += 2;
|
|
if (len == 18)
|
|
len += *dp++;
|
|
|
|
/*
|
|
* Now we copy the bytes specified by the tag from OUTPUT
|
|
* to OUTPUT. It is dangerous and platform dependant to
|
|
* use memcpy() here, because the copied areas could
|
|
* overlap extremely!
|
|
*/
|
|
while (len--)
|
|
{
|
|
*bp = bp[-off];
|
|
bp++;
|
|
}
|
|
}
|
|
else
|
|
{
|
|
/*
|
|
* An unset control bit means LITERAL BYTE. So we just
|
|
* copy one from INPUT to OUTPUT.
|
|
*/
|
|
*bp++ = *dp++;
|
|
}
|
|
|
|
/*
|
|
* Advance the control bit
|
|
*/
|
|
ctrl >>= 1;
|
|
}
|
|
}
|
|
|
|
/*
|
|
* That's it.
|
|
*/
|
|
return (char *) bp - dest;
|
|
}
|
|
|
|
|
|
/* ----------
|
|
* pglz_get_next_decomp_char_from_lzdata -
|
|
*
|
|
* Reads the next character from a decompression state if the
|
|
* input data to pglz_decomp_init() was in compressed format.
|
|
* ----------
|
|
*/
|
|
int
|
|
pglz_get_next_decomp_char_from_lzdata(PGLZ_DecompState *dstate)
|
|
{
|
|
unsigned char retval;
|
|
|
|
if (dstate->tocopy > 0)
|
|
{
|
|
/*
|
|
* Copy one byte from output to output until we did it for the
|
|
* length specified by the last tag. Return that byte.
|
|
*/
|
|
dstate->tocopy--;
|
|
return (*(dstate->cp_out++) = *(dstate->cp_copy++));
|
|
}
|
|
|
|
if (dstate->ctrl_count == 0)
|
|
{
|
|
/*
|
|
* Get the next control byte if we need to, but check for EOF
|
|
* before.
|
|
*/
|
|
if (dstate->cp_in == dstate->cp_end)
|
|
return EOF;
|
|
|
|
/*
|
|
* This decompression method saves time only, if we stop near the
|
|
* beginning of the data (maybe because we're called by a
|
|
* comparision function and a difference occurs early). Otherwise,
|
|
* all the checks, needed here, cause too much overhead.
|
|
*
|
|
* Thus we decompress the entire rest at once into the temporary
|
|
* buffer and change the decomp state to return the prepared data
|
|
* from the buffer by the more simple calls to
|
|
* pglz_get_next_decomp_char_from_plain().
|
|
*/
|
|
if (dstate->cp_out - dstate->temp_buf >= 256)
|
|
{
|
|
unsigned char *cp_in = dstate->cp_in;
|
|
unsigned char *cp_out = dstate->cp_out;
|
|
unsigned char *cp_end = dstate->cp_end;
|
|
unsigned char *cp_copy;
|
|
unsigned char ctrl;
|
|
int off;
|
|
int len;
|
|
int i;
|
|
|
|
while (cp_in < cp_end)
|
|
{
|
|
ctrl = *cp_in++;
|
|
|
|
for (i = 0; i < 8; i++)
|
|
{
|
|
if (cp_in == cp_end)
|
|
break;
|
|
|
|
if (ctrl & 0x01)
|
|
{
|
|
len = (cp_in[0] & 0x0f) + 3;
|
|
off = ((cp_in[0] & 0xf0) << 4) | cp_in[1];
|
|
cp_in += 2;
|
|
if (len == 18)
|
|
len += *cp_in++;
|
|
|
|
cp_copy = cp_out - off;
|
|
while (len--)
|
|
*cp_out++ = *cp_copy++;
|
|
}
|
|
else
|
|
*cp_out++ = *cp_in++;
|
|
ctrl >>= 1;
|
|
}
|
|
}
|
|
|
|
dstate->cp_in = dstate->cp_out;
|
|
dstate->cp_end = cp_out;
|
|
dstate->next_char = pglz_get_next_decomp_char_from_plain;
|
|
|
|
return (int) (*(dstate->cp_in++));
|
|
}
|
|
|
|
/*
|
|
* Not yet, get next control byte into decomp state.
|
|
*/
|
|
dstate->ctrl = (unsigned char) (*(dstate->cp_in++));
|
|
dstate->ctrl_count = 8;
|
|
}
|
|
|
|
/*
|
|
* Check for EOF in tag/literal byte data.
|
|
*/
|
|
if (dstate->cp_in == dstate->cp_end)
|
|
return EOF;
|
|
|
|
/*
|
|
* Handle next control bit.
|
|
*/
|
|
dstate->ctrl_count--;
|
|
if (dstate->ctrl & 0x01)
|
|
{
|
|
/*
|
|
* Bit is set, so tag is following. Setup copy information and do
|
|
* the copy for the first byte as above.
|
|
*/
|
|
int off;
|
|
|
|
dstate->tocopy = (dstate->cp_in[0] & 0x0f) + 3;
|
|
off = ((dstate->cp_in[0] & 0xf0) << 4) | dstate->cp_in[1];
|
|
dstate->cp_in += 2;
|
|
if (dstate->tocopy == 18)
|
|
dstate->tocopy += *(dstate->cp_in++);
|
|
dstate->cp_copy = dstate->cp_out - off;
|
|
|
|
dstate->tocopy--;
|
|
retval = (*(dstate->cp_out++) = *(dstate->cp_copy++));
|
|
}
|
|
else
|
|
{
|
|
/*
|
|
* Bit is unset, so literal byte follows.
|
|
*/
|
|
retval = (int) (*(dstate->cp_out++) = *(dstate->cp_in++));
|
|
}
|
|
dstate->ctrl >>= 1;
|
|
|
|
return (int) retval;
|
|
}
|
|
|
|
|
|
/* ----------
|
|
* pglz_get_next_decomp_char_from_plain -
|
|
*
|
|
* The input data to pglz_decomp_init() was stored in uncompressed
|
|
* format. So we don't have a temporary output buffer and simply
|
|
* return bytes from the input until EOF.
|
|
* ----------
|
|
*/
|
|
int
|
|
pglz_get_next_decomp_char_from_plain(PGLZ_DecompState *dstate)
|
|
{
|
|
if (dstate->cp_in >= dstate->cp_end)
|
|
return EOF;
|
|
|
|
return (int) (*(dstate->cp_in++));
|
|
}
|