/* +++ deflate.c */ /* deflate.c -- compress data using the deflation algorithm * Copyright (C) 1995-1996 Jean-loup Gailly. * For conditions of distribution and use, see copyright notice in zlib.h */ /* * ALGORITHM * * The "deflation" process depends on being able to identify portions * of the input text which are identical to earlier input (within a * sliding window trailing behind the input currently being processed). * * The most straightforward technique turns out to be the fastest for * most input files: try all possible matches and select the longest. * The key feature of this algorithm is that insertions into the string * dictionary are very simple and thus fast, and deletions are avoided * completely. Insertions are performed at each input character, whereas * string matches are performed only when the previous match ends. So it * is preferable to spend more time in matches to allow very fast string * insertions and avoid deletions. The matching algorithm for small * strings is inspired from that of Rabin & Karp. A brute force approach * is used to find longer strings when a small match has been found. * A similar algorithm is used in comic (by Jan-Mark Wams) and freeze * (by Leonid Broukhis). * A previous version of this file used a more sophisticated algorithm * (by Fiala and Greene) which is guaranteed to run in linear amortized * time, but has a larger average cost, uses more memory and is patented. * However the F&G algorithm may be faster for some highly redundant * files if the parameter max_chain_length (described below) is too large. * * ACKNOWLEDGEMENTS * * The idea of lazy evaluation of matches is due to Jan-Mark Wams, and * I found it in 'freeze' written by Leonid Broukhis. * Thanks to many people for bug reports and testing. * * REFERENCES * * Deutsch, L.P.,"DEFLATE Compressed Data Format Specification". * Available in ftp://ds.internic.net/rfc/rfc1951.txt * * A description of the Rabin and Karp algorithm is given in the book * "Algorithms" by R. Sedgewick, Addison-Wesley, p252. * * Fiala,E.R., and Greene,D.H. * Data Compression with Finite Windows, Comm.ACM, 32,4 (1989) 490-595 * */ #include <linux/module.h> #include <linux/zutil.h> #include "defutil.h" /* architecture-specific bits */ #ifdef CONFIG_ZLIB_DFLTCC # include "../zlib_dfltcc/dfltcc_deflate.h" #else #define DEFLATE_RESET_HOOK(strm) … #define DEFLATE_HOOK(strm, flush, bstate) … #define DEFLATE_NEED_CHECKSUM(strm) … #define DEFLATE_DFLTCC_ENABLED() … #endif /* =========================================================================== * Function prototypes. */ compress_func; /* Compression function. Returns the block state after the call. */ static void fill_window (deflate_state *s); static block_state deflate_stored (deflate_state *s, int flush); static block_state deflate_fast (deflate_state *s, int flush); static block_state deflate_slow (deflate_state *s, int flush); static void lm_init (deflate_state *s); static void putShortMSB (deflate_state *s, uInt b); static int read_buf (z_streamp strm, Byte *buf, unsigned size); static uInt longest_match (deflate_state *s, IPos cur_match); #ifdef DEBUG_ZLIB static void check_match (deflate_state *s, IPos start, IPos match, int length); #endif /* =========================================================================== * Local data */ #define NIL … /* Tail of hash chains */ #ifndef TOO_FAR #define TOO_FAR … #endif /* Matches of length 3 are discarded if their distance exceeds TOO_FAR */ #define MIN_LOOKAHEAD … /* Minimum amount of lookahead, except at the end of the input file. * See deflate.c for comments about the MIN_MATCH+1. */ /* Workspace to be allocated for deflate processing */ deflate_workspace; #ifdef CONFIG_ZLIB_DFLTCC /* dfltcc_state must be doubleword aligned for DFLTCC call */ static_assert(offsetof(struct deflate_workspace, dfltcc_memory) % 8 == 0); #endif /* Values for max_lazy_match, good_match and max_chain_length, depending on * the desired pack level (0..9). The values given below have been tuned to * exclude worst case performance for pathological files. Better values may be * found for specific files. */ config; static const config configuration_table[10] = …; /* maximum compression */ /* Note: the deflate() code requires max_lazy >= MIN_MATCH and max_chain >= 4 * For deflate_fast() (levels <= 3) good is ignored and lazy has a different * meaning. */ #define EQUAL … /* result of memcmp for equal strings */ /* =========================================================================== * Update a hash value with the given input byte * IN assertion: all calls to UPDATE_HASH are made with consecutive * input characters, so that a running hash key can be computed from the * previous key instead of complete recalculation each time. */ #define UPDATE_HASH(s,h,c) … /* =========================================================================== * Insert string str in the dictionary and set match_head to the previous head * of the hash chain (the most recent string with same hash key). Return * the previous length of the hash chain. * IN assertion: all calls to INSERT_STRING are made with consecutive * input characters and the first MIN_MATCH bytes of str are valid * (except for the last MIN_MATCH-1 bytes of the input file). */ #define INSERT_STRING(s, str, match_head) … /* =========================================================================== * Initialize the hash table (avoiding 64K overflow for 16 bit systems). * prev[] will be initialized on the fly. */ #define CLEAR_HASH(s) … /* ========================================================================= */ int zlib_deflateInit2( z_streamp strm, int level, int method, int windowBits, int memLevel, int strategy ) { … } /* ========================================================================= */ int zlib_deflateReset( z_streamp strm ) { … } /* ========================================================================= * Put a short in the pending buffer. The 16-bit value is put in MSB order. * IN assertion: the stream state is correct and there is enough room in * pending_buf. */ static void putShortMSB( deflate_state *s, uInt b ) { … } /* ========================================================================= */ int zlib_deflate( z_streamp strm, int flush ) { … } /* ========================================================================= */ int zlib_deflateEnd( z_streamp strm ) { … } /* =========================================================================== * Read a new buffer from the current input stream, update the adler32 * and total number of bytes read. All deflate() input goes through * this function so some applications may wish to modify it to avoid * allocating a large strm->next_in buffer and copying from it. * (See also flush_pending()). */ static int read_buf( z_streamp strm, Byte *buf, unsigned size ) { … } /* =========================================================================== * Initialize the "longest match" routines for a new zlib stream */ static void lm_init( deflate_state *s ) { … } /* =========================================================================== * Set match_start to the longest match starting at the given string and * return its length. Matches shorter or equal to prev_length are discarded, * in which case the result is equal to prev_length and match_start is * garbage. * IN assertions: cur_match is the head of the hash chain for the current * string (strstart) and its distance is <= MAX_DIST, and prev_length >= 1 * OUT assertion: the match length is not greater than s->lookahead. */ /* For 80x86 and 680x0, an optimized version will be provided in match.asm or * match.S. The code will be functionally equivalent. */ static uInt longest_match( deflate_state *s, IPos cur_match /* current match */ ) { … } #ifdef DEBUG_ZLIB /* =========================================================================== * Check that the match at match_start is indeed a match. */ static void check_match( deflate_state *s, IPos start, IPos match, int length ) { /* check that the match is indeed a match */ if (memcmp((char *)s->window + match, (char *)s->window + start, length) != EQUAL) { fprintf(stderr, " start %u, match %u, length %d\n", start, match, length); do { fprintf(stderr, "%c%c", s->window[match++], s->window[start++]); } while (--length != 0); z_error("invalid match"); } if (z_verbose > 1) { fprintf(stderr,"\\[%d,%d]", start-match, length); do { putc(s->window[start++], stderr); } while (--length != 0); } } #else #define check_match(s, start, match, length) … #endif /* =========================================================================== * Fill the window when the lookahead becomes insufficient. * Updates strstart and lookahead. * * IN assertion: lookahead < MIN_LOOKAHEAD * OUT assertions: strstart <= window_size-MIN_LOOKAHEAD * At least one byte has been read, or avail_in == 0; reads are * performed for at least two bytes (required for the zip translate_eol * option -- not supported here). */ static void fill_window( deflate_state *s ) { … } /* =========================================================================== * Flush the current block, with given end-of-file flag. * IN assertion: strstart is set to the end of the current match. */ #define FLUSH_BLOCK_ONLY(s, eof) … /* Same but force premature exit if necessary. */ #define FLUSH_BLOCK(s, eof) … /* =========================================================================== * Copy without compression as much as possible from the input stream, return * the current block state. * This function does not insert new strings in the dictionary since * uncompressible data is probably not useful. This function is used * only for the level=0 compression option. * NOTE: this function should be optimized to avoid extra copying from * window to pending_buf. */ static block_state deflate_stored( deflate_state *s, int flush ) { … } /* =========================================================================== * Compress as much as possible from the input stream, return the current * block state. * This function does not perform lazy evaluation of matches and inserts * new strings in the dictionary only for unmatched strings or for short * matches. It is used only for the fast compression options. */ static block_state deflate_fast( deflate_state *s, int flush ) { … } /* =========================================================================== * Same as above, but achieves better compression. We use a lazy * evaluation for matches: a match is finally adopted only if there is * no better match at the next window position. */ static block_state deflate_slow( deflate_state *s, int flush ) { … } int zlib_deflate_workspacesize(int windowBits, int memLevel) { … } int zlib_deflate_dfltcc_enabled(void) { … }
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