Index: gzip-1.5/deflate.c

===================================================================

--- gzip-1.5.orig/deflate.c

+++ gzip-1.5/deflate.c

@@ -131,6 +131,14 @@

 #endif

 /* Matches of length 3 are discarded if their distance exceeds TOO_FAR */

+#ifndef RSYNC_WIN

+#  define RSYNC_WIN 4096

+#endif

+/* Size of rsync window, must be < MAX_DIST */

+

+#define RSYNC_SUM_MATCH(sum) ((sum) % RSYNC_WIN == 0)

+/* Whether window sum matches magic value */

+

 /* ===========================================================================

  * Local data used by the "longest match" routines.

  */

@@ -212,6 +220,8 @@ local int compr_level;

 unsigned good_match;

 /* Use a faster search when the previous match is longer than this */

+local ulg rsync_sum;  /* rolling sum of rsync window */

+local ulg rsync_chunk_end; /* next rsync sequence point */

 /* 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

@@ -314,6 +324,10 @@ void lm_init (pack_level, flags)

 #endif

     /* prev will be initialized on the fly */

+    /* rsync params */

+    rsync_chunk_end = 0xFFFFFFFFUL;

+    rsync_sum = 0;

+

     /* Set the default configuration parameters:

      */

     max_lazy_match   = configuration_table[pack_level].max_lazy;

@@ -550,6 +564,8 @@ local void fill_window()

         memcpy((char*)window, (char*)window+WSIZE, (unsigned)WSIZE);

         match_start -= WSIZE;

         strstart    -= WSIZE; /* we now have strstart >= MAX_DIST: */

+        if (rsync_chunk_end != 0xFFFFFFFFUL)

+            rsync_chunk_end -= WSIZE;

         block_start -= (long) WSIZE;

@@ -579,13 +595,46 @@ local void fill_window()

     }

 }

+local void rsync_roll(start, num)

+    unsigned start;

+    unsigned num;

+{

+    unsigned i;

+

+    if (start < RSYNC_WIN) {

+       /* before window fills. */

+       for (i = start; i < RSYNC_WIN; i++) {

+           if (i == start + num) return;

+           rsync_sum += (ulg)window[i];

+       }

+       num -= (RSYNC_WIN - start);

+       start = RSYNC_WIN;

+    }

+

+    /* buffer after window full */

+    for (i = start; i < start+num; i++) {

+       /* New character in */

+       rsync_sum += (ulg)window[i];

+       /* Old character out */

+       rsync_sum -= (ulg)window[i - RSYNC_WIN];

+       if (rsync_chunk_end == 0xFFFFFFFFUL && RSYNC_SUM_MATCH(rsync_sum))

+           rsync_chunk_end = i;

+    }

+}

+

+/* ===========================================================================

+ * Set rsync_chunk_end if window sum matches magic value.

+ */

+#define RSYNC_ROLL(s, n) \

+   do { if (rsync) rsync_roll((s), (n)); } while(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(eof) \

    flush_block(block_start >= 0L ? (char*)&window[(unsigned)block_start] : \

-                (char*)NULL, (long)strstart - block_start, (eof))

+                (char*)NULL, (long)strstart - block_start, flush-1, (eof)) 

 /* ===========================================================================

  * Processes a new input file and return its compressed length. This

@@ -596,7 +645,7 @@ local void fill_window()

 local off_t deflate_fast()

 {

     IPos hash_head; /* head of the hash chain */

-    int flush;      /* set if current block must be flushed */

+    int flush;      /* set if current block must be flushed, 2=>and padded  */ 

     unsigned match_length = 0;  /* length of best match */

     prev_length = MIN_MATCH-1;

@@ -625,7 +674,8 @@ local off_t deflate_fast()

             flush = ct_tally(strstart-match_start, match_length - MIN_MATCH);

             lookahead -= match_length;

-

+            

+            RSYNC_ROLL(strstart, match_length);

             /* Insert new strings in the hash table only if the match length

              * is not too large. This saves time but degrades compression.

              */

@@ -654,9 +704,14 @@ local off_t deflate_fast()

             /* No match, output a literal byte */

             Tracevv((stderr,"%c",window[strstart]));

             flush = ct_tally (0, window[strstart]);

+            RSYNC_ROLL(strstart, 1);

             lookahead--;

             strstart++;

         }

+        if (rsync && strstart > rsync_chunk_end) {                                                        

+            rsync_chunk_end = 0xFFFFFFFFUL;                                                               

+            flush = 2;                                                                                    

+       }  

         if (flush) FLUSH_BLOCK(0), block_start = strstart;

         /* Make sure that we always have enough lookahead, except

@@ -730,6 +785,7 @@ off_t deflate()

              */

             lookahead -= prev_length-1;

             prev_length -= 2;

+            RSYNC_ROLL(strstart, prev_length+1);

             do {

                 strstart++;

                 INSERT_STRING(strstart, hash_head);

@@ -742,24 +798,40 @@ off_t deflate()

             match_available = 0;

             match_length = MIN_MATCH-1;

             strstart++;

-            if (flush) FLUSH_BLOCK(0), block_start = strstart;

+            if (rsync && strstart > rsync_chunk_end) {

+                rsync_chunk_end = 0xFFFFFFFFUL;

+                flush = 2;

+            }

+            if (flush) FLUSH_BLOCK(0), block_start = strstart;

         } else if (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",window[strstart-1]));

-            if (ct_tally (0, window[strstart-1])) {

-                FLUSH_BLOCK(0), block_start = strstart;

+            flush = ct_tally (0, window[strstart-1]);

+            if (rsync && strstart > rsync_chunk_end) {

+                rsync_chunk_end = 0xFFFFFFFFUL;

+                flush = 2;

             }

+            if (flush) FLUSH_BLOCK(0), block_start = strstart;

+            RSYNC_ROLL(strstart, 1);

             strstart++;

             lookahead--;

         } else {

             /* There is no previous match to compare with, wait for

              * the next step to decide.

              */

+            if (rsync && strstart > rsync_chunk_end) {

+                /* Reset huffman tree */

+                rsync_chunk_end = 0xFFFFFFFFUL;

+                flush = 2;

+                FLUSH_BLOCK(0), block_start = strstart;

+            }             

+             

             match_available = 1;

+            RSYNC_ROLL(strstart, 1);  

             strstart++;

             lookahead--;

         }

Index: gzip-1.5/doc/gzip.texi

===================================================================

--- gzip-1.5.orig/doc/gzip.texi

+++ gzip-1.5/doc/gzip.texi

@@ -353,6 +353,14 @@ specified on the command line are direct

 into the directory and compress all the files it finds there (or

 decompress them in the case of @command{gunzip}).

+@item --rsyncable

+While compressing, synchronize the output occasionally based on the

+input.  This reduces compression by about 1 percent most cases, but

+means that the @code{rsync} program can take advantage of similarities

+in the uncompressed input when syncronizing two files compressed with

+this flag.  @code{gunzip} cannot tell the difference between a

+compressed file created with this option, and one created without it.

+

 @item --suffix @var{suf}

 @itemx -S @var{suf}

 Use suffix @var{suf} instead of @samp{.gz}.  Any suffix can be

Index: gzip-1.5/gzip.c

===================================================================

--- gzip-1.5.orig/gzip.c

+++ gzip-1.5/gzip.c

@@ -213,6 +213,7 @@ int  ofd;                  /* output fil

 unsigned insize;           /* valid bytes in inbuf */

 unsigned inptr;            /* index of next byte to be processed in inbuf */

 unsigned outcnt;           /* bytes in output buffer */

+int rsync = 0;             /* make ryncable chunks */

 static int handled_sig[] =

   {

@@ -270,7 +271,7 @@ static const struct option longopts[] =

     {"best",       0, 0, '9'}, /* compress better */

     {"lzw",        0, 0, 'Z'}, /* make output compatible with old compress */

     {"bits",       1, 0, 'b'}, /* max number of bits per code (implies -Z) */

-

+    {"rsyncable",  0, 0, 'R'}, /* make rsync-friendly archive */ 

     { 0, 0, 0, 0 }

 };

@@ -353,6 +354,7 @@ local void help()

  "  -Z, --lzw         produce output compatible with old compress",

  "  -b, --bits=BITS   max number of bits per code (implies -Z)",

 #endif

+ "    --rsyncable   Make rsync-friendly archive",  

  "",

  "With no FILE, or when FILE is -, read standard input.",

  "",

@@ -482,6 +484,9 @@ int main (int argc, char **argv)

             recursive = 1;

 #endif

             break;

+            

+        case 'R':

+            rsync = 1; break;

         case 'S':

 #ifdef NO_MULTIPLE_DOTS

             if (*optarg == '.') optarg++;

Index: gzip-1.5/gzip.h

===================================================================

--- gzip-1.5.orig/gzip.h

+++ gzip-1.5/gzip.h

@@ -140,6 +140,7 @@ EXTERN(uch, window);         /* Sliding

 extern unsigned insize; /* valid bytes in inbuf */

 extern unsigned inptr;  /* index of next byte to be processed in inbuf */

 extern unsigned outcnt; /* bytes in output buffer */

+extern int rsync;  /* deflate into rsyncable chunks */ 

 extern off_t bytes_in;   /* number of input bytes */

 extern off_t bytes_out;  /* number of output bytes */

@@ -287,7 +288,7 @@ extern off_t deflate (void);

         /* in trees.c */

 extern void ct_init     (ush *attr, int *method);

 extern int  ct_tally    (int dist, int lc);

-extern off_t flush_block (char *buf, ulg stored_len, int eof);

+extern off_t flush_block (char *buf, ulg stored_len, int pad, int eof);

         /* in bits.c */

 extern void     bi_init    (file_t zipfile);

Index: gzip-1.5/trees.c

===================================================================

--- gzip-1.5.orig/trees.c

+++ gzip-1.5/trees.c

@@ -856,9 +856,10 @@ local void send_all_trees(lcodes, dcodes

  * trees or store, and output the encoded block to the zip file. This function

  * returns the total compressed length for the file so far.

  */

-off_t flush_block(buf, stored_len, eof)

+off_t flush_block(buf, stored_len, pad, eof)  

     char *buf;        /* input block, or NULL if too old */

     ulg stored_len;   /* length of input block */

+    int pad;          /* pad output to byte boundary */ 

     int eof;          /* true if this is the last block for a file */

 {

     ulg opt_lenb, static_lenb; /* opt_len and static_len in bytes */

@@ -951,6 +952,10 @@ off_t flush_block(buf, stored_len, eof)

         Assert (input_len == bytes_in, "bad input size");

         bi_windup();

         compressed_len += 7;  /* align on byte boundary */

+    } else if (pad && (compressed_len % 8) != 0) {

+        send_bits((STORED_BLOCK<<1)+eof, 3);  /* send block type */

+        compressed_len = (compressed_len + 3 + 7) & ~7L;

+        copy_block(buf, 0, 1); /* with header */

     }

     return compressed_len >> 3;