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 /* +++ 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.h"
 #else
 #define DEFLATE_RESET_HOOK(strm) do {} while (0)
 #define DEFLATE_HOOK(strm, flush, bstate) 0
 #define DEFLATE_NEED_CHECKSUM(strm) 1
 #define DEFLATE_DFLTCC_ENABLED() 0
 #endif
 
 /* ===========================================================================
  *  Function prototypes.
  */
 
 typedef block_state (*compress_func) (deflate_state *s, int flush);
 /* 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 0
 /* Tail of hash chains */
 
 #ifndef TOO_FAR
 #  define TOO_FAR 4096
 #endif
 /* Matches of length 3 are discarded if their distance exceeds TOO_FAR */
 
 #define MIN_LOOKAHEAD (MAX_MATCH+MIN_MATCH+1)
 /* 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 */
 typedef struct deflate_workspace {
     /* State memory for the deflator */
     deflate_state deflate_memory;
 #ifdef CONFIG_ZLIB_DFLTCC
     /* State memory for s390 hardware deflate */
     struct dfltcc_state dfltcc_memory;
 #endif
     Byte *window_memory;
     Pos *prev_memory;
     Pos *head_memory;
     char *overlay_memory;
 } 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.
  */
 typedef struct config_s {
    ush good_length; /* reduce lazy search above this match length */
    ush max_lazy;    /* do not perform lazy search above this match length */
    ush nice_length; /* quit search above this match length */
    ush max_chain;
    compress_func func;
 } config;
 
 static const config configuration_table[10] = {
 /*      good lazy nice chain */
 /* 0 */ {0,    0,  0,    0, deflate_stored},  /* store only */
 /* 1 */ {4,    4,  8,    4, deflate_fast}, /* maximum speed, no lazy matches */
 /* 2 */ {4,    5, 16,    8, deflate_fast},
 /* 3 */ {4,    6, 32,   32, deflate_fast},
 
 /* 4 */ {4,    4, 16,   16, deflate_slow},  /* lazy matches */
 /* 5 */ {8,   16, 32,   32, deflate_slow},
 /* 6 */ {8,   16, 128, 128, deflate_slow},
 /* 7 */ {8,   32, 128, 256, deflate_slow},
 /* 8 */ {32, 128, 258, 1024, deflate_slow},
 /* 9 */ {32, 258, 258, 4096, deflate_slow}}; /* 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 0
 /* 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) (h = (((h)<<s->hash_shift) ^ (c)) & s->hash_mask)
 
 
 /* ===========================================================================
  * 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) \
    (UPDATE_HASH(s, s->ins_h, s->window[(str) + (MIN_MATCH-1)]), \
     s->prev[(str) & s->w_mask] = match_head = s->head[s->ins_h], \
     s->head[s->ins_h] = (Pos)(str))
 
 /* ===========================================================================
  * Initialize the hash table (avoiding 64K overflow for 16 bit systems).
  * prev[] will be initialized on the fly.
  */
 #define CLEAR_HASH(s) \
     s->head[s->hash_size-1] = NIL; \
     memset((char *)s->head, 0, (unsigned)(s->hash_size-1)*sizeof(*s->head));
 
 /* ========================================================================= */
 int zlib_deflateInit2(
     z_streamp strm,
     int  level,
     int  method,
     int  windowBits,
     int  memLevel,
     int  strategy
 )
 {
     deflate_state *s;
     int noheader = 0;
     deflate_workspace *mem;
     char *next;
 
     ush *overlay;
     /* We overlay pending_buf and d_buf+l_buf. This works since the average
      * output size for (length,distance) codes is <= 24 bits.
      */
 
     if (strm == NULL) return Z_STREAM_ERROR;
 
     strm->msg = NULL;
 
     if (level == Z_DEFAULT_COMPRESSION) level = 6;
 
     mem = (deflate_workspace *) strm->workspace;
 
     if (windowBits < 0) { /* undocumented feature: suppress zlib header */
         noheader = 1;
         windowBits = -windowBits;
     }
     if (memLevel < 1 || memLevel > MAX_MEM_LEVEL || method != Z_DEFLATED ||
         windowBits < 9 || windowBits > 15 || level < 0 || level > 9 ||
     strategy < 0 || strategy > Z_HUFFMAN_ONLY) {
         return Z_STREAM_ERROR;
     }
 
     /*
      * Direct the workspace's pointers to the chunks that were allocated
      * along with the deflate_workspace struct.
      */
     next = (char *) mem;
     next += sizeof(*mem);
 #ifdef CONFIG_ZLIB_DFLTCC
     /*
      *  DFLTCC requires the window to be page aligned.
      *  Thus, we overallocate and take the aligned portion of the buffer.
      */
     mem->window_memory = (Byte *) PTR_ALIGN(next, PAGE_SIZE);
 #else
     mem->window_memory = (Byte *) next;
 #endif
     next += zlib_deflate_window_memsize(windowBits);
     mem->prev_memory = (Pos *) next;
     next += zlib_deflate_prev_memsize(windowBits);
     mem->head_memory = (Pos *) next;
     next += zlib_deflate_head_memsize(memLevel);
     mem->overlay_memory = next;
 
     s = (deflate_state *) &(mem->deflate_memory);
     strm->state = (struct internal_state *)s;
     s->strm = strm;
 
     s->noheader = noheader;
     s->w_bits = windowBits;
     s->w_size = 1 << s->w_bits;
     s->w_mask = s->w_size - 1;
 
     s->hash_bits = memLevel + 7;
     s->hash_size = 1 << s->hash_bits;
     s->hash_mask = s->hash_size - 1;
     s->hash_shift =  ((s->hash_bits+MIN_MATCH-1)/MIN_MATCH);
 
     s->window = (Byte *) mem->window_memory;
     s->prev   = (Pos *)  mem->prev_memory;
     s->head   = (Pos *)  mem->head_memory;
 
     s->lit_bufsize = 1 << (memLevel + 6); /* 16K elements by default */
 
     overlay = (ush *) mem->overlay_memory;
     s->pending_buf = (uch *) overlay;
     s->pending_buf_size = (ulg)s->lit_bufsize * (sizeof(ush)+2L);
 
     s->d_buf = overlay + s->lit_bufsize/sizeof(ush);
     s->l_buf = s->pending_buf + (1+sizeof(ush))*s->lit_bufsize;
 
     s->level = level;
     s->strategy = strategy;
     s->method = (Byte)method;
 
     return zlib_deflateReset(strm);
 }
 
 /* ========================================================================= */
 int zlib_deflateReset(
     z_streamp strm
 )
 {
     deflate_state *s;
     
     if (strm == NULL || strm->state == NULL)
         return Z_STREAM_ERROR;
 
     strm->total_in = strm->total_out = 0;
     strm->msg = NULL;
     strm->data_type = Z_UNKNOWN;
 
     s = (deflate_state *)strm->state;
     s->pending = 0;
     s->pending_out = s->pending_buf;
 
     if (s->noheader < 0) {
         s->noheader = 0; /* was set to -1 by deflate(..., Z_FINISH); */
     }
     s->status = s->noheader ? BUSY_STATE : INIT_STATE;
     strm->adler = 1;
     s->last_flush = Z_NO_FLUSH;
 
     zlib_tr_init(s);
     lm_init(s);
 
     DEFLATE_RESET_HOOK(strm);
 
     return Z_OK;
 }
 
 /* =========================================================================
  * 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
 )
 {
     put_byte(s, (Byte)(b >> 8));
     put_byte(s, (Byte)(b & 0xff));
 }   
 
 /* ========================================================================= */
 int zlib_deflate(
     z_streamp strm,
     int flush
 )
 {
     int old_flush; /* value of flush param for previous deflate call */
     deflate_state *s;
 
     if (strm == NULL || strm->state == NULL ||
     flush > Z_FINISH || flush < 0) {
         return Z_STREAM_ERROR;
     }
     s = (deflate_state *) strm->state;
 
     if ((strm->next_in == NULL && strm->avail_in != 0) ||
     (s->status == FINISH_STATE && flush != Z_FINISH)) {
         return Z_STREAM_ERROR;
     }
     if (strm->avail_out == 0) return Z_BUF_ERROR;
 
     s->strm = strm; /* just in case */
     old_flush = s->last_flush;
     s->last_flush = flush;
 
     /* Write the zlib header */
     if (s->status == INIT_STATE) {
 
         uInt header = (Z_DEFLATED + ((s->w_bits-8)<<4)) << 8;
         uInt level_flags = (s->level-1) >> 1;
 
         if (level_flags > 3) level_flags = 3;
         header |= (level_flags << 6);
     if (s->strstart != 0) header |= PRESET_DICT;
         header += 31 - (header % 31);
 
         s->status = BUSY_STATE;
         putShortMSB(s, header);
 
     /* Save the adler32 of the preset dictionary: */
     if (s->strstart != 0) {
         putShortMSB(s, (uInt)(strm->adler >> 16));
         putShortMSB(s, (uInt)(strm->adler & 0xffff));
     }
     strm->adler = 1L;
     }
 
     /* Flush as much pending output as possible */
     if (s->pending != 0) {
         flush_pending(strm);
         if (strm->avail_out == 0) {
         /* Since avail_out is 0, deflate will be called again with
          * more output space, but possibly with both pending and
          * avail_in equal to zero. There won't be anything to do,
          * but this is not an error situation so make sure we
          * return OK instead of BUF_ERROR at next call of deflate:
              */
         s->last_flush = -1;
         return Z_OK;
     }
 
     /* Make sure there is something to do and avoid duplicate consecutive
      * flushes. For repeated and useless calls with Z_FINISH, we keep
      * returning Z_STREAM_END instead of Z_BUFF_ERROR.
      */
     } else if (strm->avail_in == 0 && flush <= old_flush &&
            flush != Z_FINISH) {
         return Z_BUF_ERROR;
     }
 
     /* User must not provide more input after the first FINISH: */
     if (s->status == FINISH_STATE && strm->avail_in != 0) {
         return Z_BUF_ERROR;
     }
 
     /* Start a new block or continue the current one.
      */
     if (strm->avail_in != 0 || s->lookahead != 0 ||
         (flush != Z_NO_FLUSH && s->status != FINISH_STATE)) {
         block_state bstate;
 
     bstate = DEFLATE_HOOK(strm, flush, &bstate) ? bstate :
          (*(configuration_table[s->level].func))(s, flush);
 
         if (bstate == finish_started || bstate == finish_done) {
             s->status = FINISH_STATE;
         }
         if (bstate == need_more || bstate == finish_started) {
         if (strm->avail_out == 0) {
             s->last_flush = -1; /* avoid BUF_ERROR next call, see above */
         }
         return Z_OK;
         /* If flush != Z_NO_FLUSH && avail_out == 0, the next call
          * of deflate should use the same flush parameter to make sure
          * that the flush is complete. So we don't have to output an
          * empty block here, this will be done at next call. This also
          * ensures that for a very small output buffer, we emit at most
          * one empty block.
          */
     }
         if (bstate == block_done) {
             if (flush == Z_PARTIAL_FLUSH) {
                 zlib_tr_align(s);
         } else if (flush == Z_PACKET_FLUSH) {
         /* Output just the 3-bit `stored' block type value,
            but not a zero length. */
         zlib_tr_stored_type_only(s);
             } else { /* FULL_FLUSH or SYNC_FLUSH */
                 zlib_tr_stored_block(s, (char*)0, 0L, 0);
                 /* For a full flush, this empty block will be recognized
                  * as a special marker by inflate_sync().
                  */
                 if (flush == Z_FULL_FLUSH) {
                     CLEAR_HASH(s);             /* forget history */
                 }
             }
             flush_pending(strm);
         if (strm->avail_out == 0) {
           s->last_flush = -1; /* avoid BUF_ERROR at next call, see above */
           return Z_OK;
         }
         }
     }
     Assert(strm->avail_out > 0, "bug2");
 
     if (flush != Z_FINISH) return Z_OK;
     if (s->noheader) return Z_STREAM_END;
 
     /* Write the zlib trailer (adler32) */
     putShortMSB(s, (uInt)(strm->adler >> 16));
     putShortMSB(s, (uInt)(strm->adler & 0xffff));
     flush_pending(strm);
     /* If avail_out is zero, the application will call deflate again
      * to flush the rest.
      */
     s->noheader = -1; /* write the trailer only once! */
     return s->pending != 0 ? Z_OK : Z_STREAM_END;
 }
 
 /* ========================================================================= */
 int zlib_deflateEnd(
     z_streamp strm
 )
 {
     int status;
     deflate_state *s;
 
     if (strm == NULL || strm->state == NULL) return Z_STREAM_ERROR;
     s = (deflate_state *) strm->state;
 
     status = s->status;
     if (status != INIT_STATE && status != BUSY_STATE &&
     status != FINISH_STATE) {
       return Z_STREAM_ERROR;
     }
 
     strm->state = NULL;
 
     return status == BUSY_STATE ? Z_DATA_ERROR : Z_OK;
 }
 
 /* ===========================================================================
  * 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
 )
 {
     unsigned len = strm->avail_in;
 
     if (len > size) len = size;
     if (len == 0) return 0;
 
     strm->avail_in  -= len;
 
     if (!DEFLATE_NEED_CHECKSUM(strm)) {}
     else if (!((deflate_state *)(strm->state))->noheader) {
         strm->adler = zlib_adler32(strm->adler, strm->next_in, len);
     }
     memcpy(buf, strm->next_in, len);
     strm->next_in  += len;
     strm->total_in += len;
 
     return (int)len;
 }
 
 /* ===========================================================================
  * Initialize the "longest match" routines for a new zlib stream
  */
 static void lm_init(
     deflate_state *s
 )
 {
     s->window_size = (ulg)2L*s->w_size;
 
     CLEAR_HASH(s);
 
     /* Set the default configuration parameters:
      */
     s->max_lazy_match   = configuration_table[s->level].max_lazy;
     s->good_match       = configuration_table[s->level].good_length;
     s->nice_match       = configuration_table[s->level].nice_length;
     s->max_chain_length = configuration_table[s->level].max_chain;
 
     s->strstart = 0;
     s->block_start = 0L;
     s->lookahead = 0;
     s->match_length = s->prev_length = MIN_MATCH-1;
     s->match_available = 0;
     s->ins_h = 0;
 }
 
 /* ===========================================================================
  * 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 */
 )
 {
     unsigned chain_length = s->max_chain_length;/* max hash chain length */
     register Byte *scan = s->window + s->strstart; /* current string */
     register Byte *match;                       /* matched string */
     register int len;                           /* length of current match */
     int best_len = s->prev_length;              /* best match length so far */
     int nice_match = s->nice_match;             /* stop if match long enough */
     IPos limit = s->strstart > (IPos)MAX_DIST(s) ?
         s->strstart - (IPos)MAX_DIST(s) : NIL;
     /* Stop when cur_match becomes <= limit. To simplify the code,
      * we prevent matches with the string of window index 0.
      */
     Pos *prev = s->prev;
     uInt wmask = s->w_mask;
 
 #ifdef UNALIGNED_OK
     /* Compare two bytes at a time. Note: this is not always beneficial.
      * Try with and without -DUNALIGNED_OK to check.
      */
     register Byte *strend = s->window + s->strstart + MAX_MATCH - 1;
     register ush scan_start = *(ush*)scan;
     register ush scan_end   = *(ush*)(scan+best_len-1);
 #else
     register Byte *strend = s->window + s->strstart + MAX_MATCH;
     register Byte scan_end1  = scan[best_len-1];
     register Byte scan_end   = scan[best_len];
 #endif
 
     /* The code is optimized for HASH_BITS >= 8 and MAX_MATCH-2 multiple of 16.
      * It is easy to get rid of this optimization if necessary.
      */
     Assert(s->hash_bits >= 8 && MAX_MATCH == 258, "Code too clever");
 
     /* Do not waste too much time if we already have a good match: */
     if (s->prev_length >= s->good_match) {
         chain_length >>= 2;
     }
     /* Do not look for matches beyond the end of the input. This is necessary
      * to make deflate deterministic.
      */
     if ((uInt)nice_match > s->lookahead) nice_match = s->lookahead;
 
     Assert((ulg)s->strstart <= s->window_size-MIN_LOOKAHEAD, "need lookahead");
 
     do {
         Assert(cur_match < s->strstart, "no future");
         match = s->window + cur_match;
 
         /* Skip to next match if the match length cannot increase
          * or if the match length is less than 2:
          */
 #if (defined(UNALIGNED_OK) && MAX_MATCH == 258)
         /* This code assumes sizeof(unsigned short) == 2. Do not use
          * UNALIGNED_OK if your compiler uses a different size.
          */
         if (*(ush*)(match+best_len-1) != scan_end ||
             *(ush*)match != scan_start) continue;
 
         /* It is not necessary to compare scan[2] and match[2] since they are
          * always equal when the other bytes match, given that the hash keys
          * are equal and that HASH_BITS >= 8. Compare 2 bytes at a time at
          * strstart+3, +5, ... up to strstart+257. We check for insufficient
          * lookahead only every 4th comparison; the 128th check will be made
          * at strstart+257. If MAX_MATCH-2 is not a multiple of 8, it is
          * necessary to put more guard bytes at the end of the window, or
          * to check more often for insufficient lookahead.
          */
         Assert(scan[2] == match[2], "scan[2]?");
         scan++, match++;
         do {
         } while (*(ush*)(scan+=2) == *(ush*)(match+=2) &&
                  *(ush*)(scan+=2) == *(ush*)(match+=2) &&
                  *(ush*)(scan+=2) == *(ush*)(match+=2) &&
                  *(ush*)(scan+=2) == *(ush*)(match+=2) &&
                  scan < strend);
         /* The funny "do {}" generates better code on most compilers */
 
         /* Here, scan <= window+strstart+257 */
         Assert(scan <= s->window+(unsigned)(s->window_size-1), "wild scan");
         if (*scan == *match) scan++;
 
         len = (MAX_MATCH - 1) - (int)(strend-scan);
         scan = strend - (MAX_MATCH-1);
 
 #else /* UNALIGNED_OK */
 
         if (match[best_len]   != scan_end  ||
             match[best_len-1] != scan_end1 ||
             *match            != *scan     ||
             *++match          != scan[1])      continue;
 
         /* The check at best_len-1 can be removed because it will be made
          * again later. (This heuristic is not always a win.)
          * It is not necessary to compare scan[2] and match[2] since they
          * are always equal when the other bytes match, given that
          * the hash keys are equal and that HASH_BITS >= 8.
          */
         scan += 2, match++;
         Assert(*scan == *match, "match[2]?");
 
         /* We check for insufficient lookahead only every 8th comparison;
          * the 256th check will be made at strstart+258.
          */
         do {
         } while (*++scan == *++match && *++scan == *++match &&
                  *++scan == *++match && *++scan == *++match &&
                  *++scan == *++match && *++scan == *++match &&
                  *++scan == *++match && *++scan == *++match &&
                  scan < strend);
 
         Assert(scan <= s->window+(unsigned)(s->window_size-1), "wild scan");
 
         len = MAX_MATCH - (int)(strend - scan);
         scan = strend - MAX_MATCH;
 
 #endif /* UNALIGNED_OK */
 
         if (len > best_len) {
             s->match_start = cur_match;
             best_len = len;
             if (len >= nice_match) break;
 #ifdef UNALIGNED_OK
             scan_end = *(ush*)(scan+best_len-1);
 #else
             scan_end1  = scan[best_len-1];
             scan_end   = scan[best_len];
 #endif
         }
     } while ((cur_match = prev[cur_match & wmask]) > limit
              && --chain_length != 0);
 
     if ((uInt)best_len <= s->lookahead) return best_len;
     return s->lookahead;
 }
 
 #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
 )
 {
     register unsigned n, m;
     register Pos *p;
     unsigned more;    /* Amount of free space at the end of the window. */
     uInt wsize = s->w_size;
 
     do {
         more = (unsigned)(s->window_size -(ulg)s->lookahead -(ulg)s->strstart);
 
         /* Deal with !@#$% 64K limit: */
         if (more == 0 && s->strstart == 0 && s->lookahead == 0) {
             more = wsize;
 
         } else if (more == (unsigned)(-1)) {
             /* Very unlikely, but possible on 16 bit machine if strstart == 0
              * and lookahead == 1 (input done one byte at time)
              */
             more--;
 
         /* If the window is almost full and there is insufficient lookahead,
          * move the upper half to the lower one to make room in the upper half.
          */
         } else if (s->strstart >= wsize+MAX_DIST(s)) {
 
             memcpy((char *)s->window, (char *)s->window+wsize,
                    (unsigned)wsize);
             s->match_start -= wsize;
             s->strstart    -= wsize; /* we now have strstart >= MAX_DIST */
             s->block_start -= (long) wsize;
 
             /* Slide the hash table (could be avoided with 32 bit values
                at the expense of memory usage). We slide even when level == 0
                to keep the hash table consistent if we switch back to level > 0
                later. (Using level 0 permanently is not an optimal usage of
                zlib, so we don't care about this pathological case.)
              */
             n = s->hash_size;
             p = &s->head[n];
             do {
                 m = *--p;
                 *p = (Pos)(m >= wsize ? m-wsize : NIL);
             } while (--n);
 
             n = wsize;
             p = &s->prev[n];
             do {
                 m = *--p;
                 *p = (Pos)(m >= wsize ? m-wsize : NIL);
                 /* If n is not on any hash chain, prev[n] is garbage but
                  * its value will never be used.
                  */
             } while (--n);
             more += wsize;
         }
         if (s->strm->avail_in == 0) return;
 
         /* If there was no sliding:
          *    strstart <= WSIZE+MAX_DIST-1 && lookahead <= MIN_LOOKAHEAD - 1 &&
          *    more == window_size - lookahead - strstart
          * => more >= window_size - (MIN_LOOKAHEAD-1 + WSIZE + MAX_DIST-1)
          * => more >= window_size - 2*WSIZE + 2
          * In the BIG_MEM or MMAP case (not yet supported),
          *   window_size == input_size + MIN_LOOKAHEAD  &&
          *   strstart + s->lookahead <= input_size => more >= MIN_LOOKAHEAD.
          * Otherwise, window_size == 2*WSIZE so more >= 2.
          * If there was sliding, more >= WSIZE. So in all cases, more >= 2.
          */
         Assert(more >= 2, "more < 2");
 
         n = read_buf(s->strm, s->window + s->strstart + s->lookahead, more);
         s->lookahead += n;
 
         /* Initialize the hash value now that we have some input: */
         if (s->lookahead >= MIN_MATCH) {
             s->ins_h = s->window[s->strstart];
             UPDATE_HASH(s, s->ins_h, s->window[s->strstart+1]);
 #if MIN_MATCH != 3
             Call UPDATE_HASH() MIN_MATCH-3 more times
 #endif
         }
         /* If the whole input has less than MIN_MATCH bytes, ins_h is garbage,
          * but this is not important since only literal bytes will be emitted.
          */
 
     } while (s->lookahead < MIN_LOOKAHEAD && s->strm->avail_in != 0);
 }
 
 /* ===========================================================================
  * 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) { \
    zlib_tr_flush_block(s, (s->block_start >= 0L ? \
                    (char *)&s->window[(unsigned)s->block_start] : \
                    NULL), \
         (ulg)((long)s->strstart - s->block_start), \
         (eof)); \
    s->block_start = s->strstart; \
    flush_pending(s->strm); \
    Tracev((stderr,"[FLUSH]")); \
 }
 
 /* Same but force premature exit if necessary. */
 #define FLUSH_BLOCK(s, eof) { \
    FLUSH_BLOCK_ONLY(s, eof); \
    if (s->strm->avail_out == 0) return (eof) ? finish_started : need_more; \
 }
 
 /* ===========================================================================
  * 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
 )
 {
     /* Stored blocks are limited to 0xffff bytes, pending_buf is limited
      * to pending_buf_size, and each stored block has a 5 byte header:
      */
     ulg max_block_size = 0xffff;
     ulg max_start;
 
     if (max_block_size > s->pending_buf_size - 5) {
         max_block_size = s->pending_buf_size - 5;
     }
 
     /* Copy as much as possible from input to output: */
     for (;;) {
         /* Fill the window as much as possible: */
         if (s->lookahead <= 1) {
 
             Assert(s->strstart < s->w_size+MAX_DIST(s) ||
            s->block_start >= (long)s->w_size, "slide too late");
 
             fill_window(s);
             if (s->lookahead == 0 && flush == Z_NO_FLUSH) return need_more;
 
             if (s->lookahead == 0) break; /* flush the current block */
         }
     Assert(s->block_start >= 0L, "block gone");
 
     s->strstart += s->lookahead;
     s->lookahead = 0;
 
     /* Emit a stored block if pending_buf will be full: */
     max_start = s->block_start + max_block_size;
         if (s->strstart == 0 || (ulg)s->strstart >= max_start) {
         /* strstart == 0 is possible when wraparound on 16-bit machine */
         s->lookahead = (uInt)(s->strstart - max_start);
         s->strstart = (uInt)max_start;
             FLUSH_BLOCK(s, 0);
     }
     /* Flush if we may have to slide, otherwise block_start may become
          * negative and the data will be gone:
          */
         if (s->strstart - (uInt)s->block_start >= MAX_DIST(s)) {
             FLUSH_BLOCK(s, 0);
     }
     }
     FLUSH_BLOCK(s, flush == Z_FINISH);
     return flush == Z_FINISH ? finish_done : block_done;
 }
 
 /* ===========================================================================
  * 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
 )
 {
     IPos hash_head = NIL; /* head of the hash chain */
     int bflush;           /* set if current block must be flushed */
 
     for (;;) {
         /* Make sure that we always have enough lookahead, except
          * at the end of the input file. We need MAX_MATCH bytes
          * for the next match, plus MIN_MATCH bytes to insert the
          * string following the next match.
          */
         if (s->lookahead < MIN_LOOKAHEAD) {
             fill_window(s);
             if (s->lookahead < MIN_LOOKAHEAD && flush == Z_NO_FLUSH) {
             return need_more;
         }
             if (s->lookahead == 0) break; /* flush the current block */
         }
 
         /* Insert the string window[strstart .. strstart+2] in the
          * dictionary, and set hash_head to the head of the hash chain:
          */
         if (s->lookahead >= MIN_MATCH) {
             INSERT_STRING(s, s->strstart, hash_head);
         }
 
         /* Find the longest match, discarding those <= prev_length.
          * At this point we have always match_length < MIN_MATCH
          */
         if (hash_head != NIL && s->strstart - hash_head <= MAX_DIST(s)) {
             /* To simplify the code, we prevent matches with the string
              * of window index 0 (in particular we have to avoid a match
              * of the string with itself at the start of the input file).
              */
             if (s->strategy != Z_HUFFMAN_ONLY) {
                 s->match_length = longest_match (s, hash_head);
             }
             /* longest_match() sets match_start */
         }
         if (s->match_length >= MIN_MATCH) {
             check_match(s, s->strstart, s->match_start, s->match_length);
 
             bflush = zlib_tr_tally(s, s->strstart - s->match_start,
                                s->match_length - MIN_MATCH);
 
             s->lookahead -= s->match_length;
 
             /* Insert new strings in the hash table only if the match length
              * is not too large. This saves time but degrades compression.
              */
             if (s->match_length <= s->max_insert_length &&
                 s->lookahead >= MIN_MATCH) {
                 s->match_length--; /* string at strstart already in hash table */
                 do {
                     s->strstart++;
                     INSERT_STRING(s, s->strstart, hash_head);
                     /* strstart never exceeds WSIZE-MAX_MATCH, so there are
                      * always MIN_MATCH bytes ahead.
                      */
                 } while (--s->match_length != 0);
                 s->strstart++; 
             } else {
                 s->strstart += s->match_length;
                 s->match_length = 0;
                 s->ins_h = s->window[s->strstart];
                 UPDATE_HASH(s, s->ins_h, s->window[s->strstart+1]);
 #if MIN_MATCH != 3
                 Call UPDATE_HASH() MIN_MATCH-3 more times
 #endif
                 /* If lookahead < MIN_MATCH, ins_h is garbage, but it does not
                  * matter since it will be recomputed at next deflate call.
                  */
             }
         } else {
             /* No match, output a literal byte */
             Tracevv((stderr,"%c", s->window[s->strstart]));
             bflush = zlib_tr_tally (s, 0, s->window[s->strstart]);
             s->lookahead--;
             s->strstart++; 
         }
         if (bflush) FLUSH_BLOCK(s, 0);
     }
     FLUSH_BLOCK(s, flush == Z_FINISH);
     return flush == Z_FINISH ? finish_done : block_done;
 }
 
 /* ===========================================================================
  * 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
 )
 {
     IPos hash_head = NIL;    /* head of hash chain */
     int bflush;              /* set if current block must be flushed */
 
     /* Process the input block. */
     for (;;) {
         /* Make sure that we always have enough lookahead, except
          * at the end of the input file. We need MAX_MATCH bytes
          * for the next match, plus MIN_MATCH bytes to insert the
          * string following the next match.
          */
         if (s->lookahead < MIN_LOOKAHEAD) {
             fill_window(s);
             if (s->lookahead < MIN_LOOKAHEAD && flush == Z_NO_FLUSH) {
             return need_more;
         }
             if (s->lookahead == 0) break; /* flush the current block */
         }
 
         /* Insert the string window[strstart .. strstart+2] in the
          * dictionary, and set hash_head to the head of the hash chain:
          */
         if (s->lookahead >= MIN_MATCH) {
             INSERT_STRING(s, s->strstart, hash_head);
         }
 
         /* Find the longest match, discarding those <= prev_length.
          */
         s->prev_length = s->match_length, s->prev_match = s->match_start;
         s->match_length = MIN_MATCH-1;
 
         if (hash_head != NIL && s->prev_length < s->max_lazy_match &&
             s->strstart - hash_head <= MAX_DIST(s)) {
             /* To simplify the code, we prevent matches with the string
              * of window index 0 (in particular we have to avoid a match
              * of the string with itself at the start of the input file).
              */
             if (s->strategy != Z_HUFFMAN_ONLY) {
                 s->match_length = longest_match (s, hash_head);
             }
             /* longest_match() sets match_start */
 
             if (s->match_length <= 5 && (s->strategy == Z_FILTERED ||
                  (s->match_length == MIN_MATCH &&
                   s->strstart - s->match_start > TOO_FAR))) {
 
                 /* If prev_match is also MIN_MATCH, match_start is garbage
                  * but we will ignore the current match anyway.
                  */
                 s->match_length = MIN_MATCH-1;
             }
         }
         /* If there was a match at the previous step and the current
          * match is not better, output the previous match:
          */
         if (s->prev_length >= MIN_MATCH && s->match_length <= s->prev_length) {
             uInt max_insert = s->strstart + s->lookahead - MIN_MATCH;
             /* Do not insert strings in hash table beyond this. */
 
             check_match(s, s->strstart-1, s->prev_match, s->prev_length);
 
             bflush = zlib_tr_tally(s, s->strstart -1 - s->prev_match,
                    s->prev_length - MIN_MATCH);
 
             /* Insert in hash table all strings up to the end of the match.
              * strstart-1 and strstart are already inserted. If there is not
              * enough lookahead, the last two strings are not inserted in
              * the hash table.
              */
             s->lookahead -= s->prev_length-1;
             s->prev_length -= 2;
             do {
                 if (++s->strstart <= max_insert) {
                     INSERT_STRING(s, s->strstart, hash_head);
                 }
             } while (--s->prev_length != 0);
             s->match_available = 0;
             s->match_length = MIN_MATCH-1;
             s->strstart++;
 
             if (bflush) FLUSH_BLOCK(s, 0);
 
         } else if (s->match_available) {
             /* If there was no match at the previous position, output a
              * single literal. If there was a match but the current match
              * is longer, truncate the previous match to a single literal.
              */
             Tracevv((stderr,"%c", s->window[s->strstart-1]));
             if (zlib_tr_tally (s, 0, s->window[s->strstart-1])) {
                 FLUSH_BLOCK_ONLY(s, 0);
             }
             s->strstart++;
             s->lookahead--;
             if (s->strm->avail_out == 0) return need_more;
         } else {
             /* There is no previous match to compare with, wait for
              * the next step to decide.
              */
             s->match_available = 1;
             s->strstart++;
             s->lookahead--;
         }
     }
     Assert (flush != Z_NO_FLUSH, "no flush?");
     if (s->match_available) {
         Tracevv((stderr,"%c", s->window[s->strstart-1]));
         zlib_tr_tally (s, 0, s->window[s->strstart-1]);
         s->match_available = 0;
     }
     FLUSH_BLOCK(s, flush == Z_FINISH);
     return flush == Z_FINISH ? finish_done : block_done;
 }
 
 int zlib_deflate_workspacesize(int windowBits, int memLevel)
 {
     if (windowBits < 0) /* undocumented feature: suppress zlib header */
         windowBits = -windowBits;
 
     /* Since the return value is typically passed to vmalloc() unchecked... */
     BUG_ON(memLevel < 1 || memLevel > MAX_MEM_LEVEL || windowBits < 9 ||
                             windowBits > 15);
 
     return sizeof(deflate_workspace)
         + zlib_deflate_window_memsize(windowBits)
         + zlib_deflate_prev_memsize(windowBits)
         + zlib_deflate_head_memsize(memLevel)
         + zlib_deflate_overlay_memsize(memLevel);
 }
 
 int zlib_deflate_dfltcc_enabled(void)
 {
     return DEFLATE_DFLTCC_ENABLED();
 }

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