We call map_ptr() with a data range than includes any unmatched data

(which we might need to reference again) in addition to the current
rolling-checksum block (this prevents the unmatched data from being
lost when we slide the buffer and read more data).

diff --git a/match.c b/match.c
index f3858e5..c09a222 100644 (file)
--- a/match.c
+++ b/match.c
@@ -141,11 +141,12 @@ static void matched(int f,struct sum_struct *s,struct map_struct *buf,
 static void hash_search(int f,struct sum_struct *s,
                        struct map_struct *buf, OFF_T len)
 {
-       OFF_T offset, end;
+       OFF_T offset, end, backup;
        unsigned int k;
        size_t want_i;
        char sum2[SUM_LENGTH];
        uint32 s1, s2, sum;
+       int more;
        schar *map;
 
        /* want_i is used to encourage adjacent matches, allowing the RLL
@@ -271,14 +272,21 @@ static void hash_search(int f,struct sum_struct *s,
                } while (++j < s->count && targets[j].t == t);
 
        null_tag:
+               backup = offset - last_match;
+               /* We sometimes read 1 byte prior to last_match... */
+               if (backup < 0)
+                       backup = 0;
+
                /* Trim off the first byte from the checksum */
-               map = (schar *)map_ptr(buf, offset, k+1);
+               more = offset + k < len;
+               map = (schar *)map_ptr(buf, offset - backup, k + more + backup)
+                   + backup;
                s1 -= map[0] + CHAR_OFFSET;
                s2 -= k * (map[0]+CHAR_OFFSET);
 
                /* Add on the next byte (if there is one) to the checksum */
-               if (k < (len-offset)) {
-                       s1 += (map[k]+CHAR_OFFSET);
+               if (more) {
+                       s1 += map[k] + CHAR_OFFSET;
                        s2 += s1;
                } else
                        --k;
@@ -289,9 +297,8 @@ static void hash_search(int f,struct sum_struct *s,
                   match. The 3 reads are caused by the
                   running match, the checksum update and the
                   literal send. */
-               if (offset > last_match
-                && offset-last_match >= CHUNK_SIZE+s->blength
-                && end-offset > CHUNK_SIZE) {
+               if (backup >= CHUNK_SIZE + s->blength
+                   && end - offset > CHUNK_SIZE) {
                        matched(f,s,buf,offset - s->blength, -2);
                }
        } while (++offset < end);