+++ /dev/null
---- a/deflate.c
-+++ b/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 8192
-+#endif
-+/* Size of rsync window, must be < MAX_DIST */
-+
-+#define RSYNC_SUM_MATCH(sum) (((sum) & (RSYNC_WIN - 1)) == 0)
-+/* Whether window sum matches magic value */
-+
- /* ===========================================================================
- * Local data used by the "longest match" routines.
- */
-@@ -212,6 +220,8 @@
- 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 @@
- #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 @@
- 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 +595,44 @@
- }
- }
-
-+local void rsync_roll(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 +643,7 @@
- local off_t deflate_fast()
- {
- IPos hash_head; /* head of the hash chain */
-- int flush; /* set if current block must be flushed */
-+ int flush = 0; /* set if current block must be flushed, 2=>and padded */
- unsigned match_length = 0; /* length of best match */
-
- prev_length = MIN_MATCH-1;
-@@ -626,7 +673,8 @@
-
- lookahead -= match_length;
-
-- /* Insert new strings in the hash table only if the 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.
- */
- if (match_length <= max_insert_length) {
-@@ -654,9 +702,14 @@
- /* 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) {
-+ flush = 2;
-+ rsync_chunk_end = 0xFFFFFFFFUL;
-+ }
- if (flush) FLUSH_BLOCK(0), block_start = strstart;
-
- /* Make sure that we always have enough lookahead, except
-@@ -679,7 +732,7 @@
- {
- IPos hash_head; /* head of hash chain */
- IPos prev_match; /* previous match */
-- int flush; /* set if current block must be flushed */
-+ int flush = 0; /* set if current block must be flushed */
- int match_available = 0; /* set if previous match exists */
- register unsigned match_length = MIN_MATCH-1; /* length of best match */
-
-@@ -730,6 +783,7 @@
- */
- lookahead -= prev_length-1;
- prev_length -= 2;
-+ RSYNC_ROLL(strstart, prev_length+1);
- do {
- strstart++;
- INSERT_STRING(strstart, hash_head);
-@@ -742,24 +796,38 @@
- 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) {
-+ rsync_chunk_end = 0xFFFFFFFFUL;
-+ flush = 2;
-+ FLUSH_BLOCK(0), block_start = strstart;
-+ }
- match_available = 1;
-+ RSYNC_ROLL(strstart, 1);
- strstart++;
- lookahead--;
- }
---- a/doc/gzip.texi
-+++ b/doc/gzip.texi
-@@ -208,6 +208,7 @@
- -V, --version display version number
- -1, --fast compress faster
- -9, --best compress better
-+ --rsyncable Make rsync-friendly archive
-
- With no FILE, or when FILE is -, read standard input.
-
-@@ -358,6 +359,14 @@
- 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 increases size by less than 1 percent most
-+cases, but means that the @command{rsync} program can much more efficiently
-+synchronize files compressed with this flag. @command{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
---- a/gzip.c
-+++ b/gzip.c
-@@ -215,6 +215,7 @@
- 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[] =
- {
-@@ -275,7 +276,7 @@
- {"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 }
- };
-
-@@ -359,6 +360,7 @@
- " -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.",
- "",
-@@ -489,8 +491,11 @@
- #else
- recursive = 1;
- #endif
-- break;
-- case 'S':
-+ break;
-+ case 'R':
-+ rsync = 1; break;
-+
-+ case 'S':
- #ifdef NO_MULTIPLE_DOTS
- if (*optarg == '.') optarg++;
- #endif
---- a/gzip.h
-+++ b/gzip.h
-@@ -140,6 +140,7 @@
- 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 @@
- /* 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);
---- a/gzip.1
-+++ b/gzip.1
-@@ -5,6 +5,7 @@
- .ll +8
- .B gzip
- .RB [ " \-acdfhklLnNrtvV19 " ]
-+.RB [ --rsyncable ]
- .RB [ \-S\ suffix ]
- [
- .I "name \&..."
-@@ -287,6 +288,16 @@
- .I gunzip
- ).
- .TP
-+.B --rsyncable
-+While compressing, synchronize the output occasionally based on the input.
-+This increases size by less than 1 percent most cases, but means that the
-+.BR rsync (1)
-+program can take advantage of similarities in the uncompressed input
-+when syncronizing two files compressed with this flag.
-+.I gunzip
-+cannot tell the difference between a compressed file created with this option,
-+and one created without it.
-+.TP
- .B \-S .suf --suffix .suf
- When compressing, use suffix .suf instead of .gz.
- Any non-empty suffix can be given, but suffixes
---- a/trees.c
-+++ b/trees.c
-@@ -856,9 +856,10 @@
- * 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 @@
- 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;
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