- /*
- * Do we have an exact match? If we were told to match
- * at the end, size must be exactly at try+fragsize,
- * otherwise try+fragsize must be still within the preimage,
- * and either case, the old piece should match the preimage
- * exactly.
- */
- if ((match_end
- ? (try + preimage->len == img->len)
- : (try + preimage->len <= img->len)) &&
- !memcmp(img->buf + try, preimage->buf, preimage->len))
- return 1;
+ if (preimage_limit == preimage->nr) {
+ /*
+ * Do we have an exact match? If we were told to match
+ * at the end, size must be exactly at try+fragsize,
+ * otherwise try+fragsize must be still within the preimage,
+ * and either case, the old piece should match the preimage
+ * exactly.
+ */
+ if ((match_end
+ ? (try + preimage->len == img->len)
+ : (try + preimage->len <= img->len)) &&
+ !memcmp(img->buf + try, preimage->buf, preimage->len))
+ return 1;
+ } else {
+ /*
+ * The preimage extends beyond the end of img, so
+ * there cannot be an exact match.
+ *
+ * There must be one non-blank context line that match
+ * a line before the end of img.
+ */
+ char *buf_end;
+
+ buf = preimage->buf;
+ buf_end = buf;
+ for (i = 0; i < preimage_limit; i++)
+ buf_end += preimage->line[i].len;
+
+ for ( ; buf < buf_end; buf++)
+ if (!isspace(*buf))
+ break;
+ if (buf == buf_end)
+ return 0;
+ }