Discard insufficient partial bZip2 matches

- Use the ratio that was used before for partial zLib matches
- Related: #95

precomp.cpp

@@ -5239,14 +5239,31 @@ void try_recompress_bzip2(FILE* origfile, int level, long long& compressed_strea
                   }
                 }
 
-                best_identical_bytes_decomp = identical_bytes_decomp;
-                best_identical_bytes = identical_bytes;
-                if (penalty_bytes_len > 0) {
-                  memcpy(best_penalty_bytes, penalty_bytes, penalty_bytes_len);
-                  best_penalty_bytes_len = penalty_bytes_len;
-                } else {
-                  best_penalty_bytes_len = 0;
-                }
+				// Partial matches sometimes need all the decompressed bytes, but there are much less 
+				// identical recompressed bytes - in these cases, all the decompressed bytes have to
+				// be stored together with the remaining recompressed bytes, so the result won't compress
+				// better than the original stream. What's important here is the ratio between recompressed ratio
+				// and decompressed ratio that shouldn't get too high.
+				// Example: A stream has 5 of 1000 identical recompressed bytes, but needs 1000 of 1000 decompressed bytes,
+				// so the ratio is (1000/1000)/(5/1000) = 200 which is too high. With 5 of 1000 decompressed bytes or
+				// 1000 of 1000 identical recompressed bytes, ratio would've been 1 and we'd accept it.
+
+				float partial_ratio = ((float)identical_bytes_decomp / decomp_bytes_total) / ((float)identical_bytes / compressed_stream_size);
+				if (partial_ratio < 3.0f) {
+					best_identical_bytes_decomp = identical_bytes_decomp;
+					best_identical_bytes = identical_bytes;
+					if (penalty_bytes_len > 0) {
+						memcpy(best_penalty_bytes, penalty_bytes, penalty_bytes_len);
+						best_penalty_bytes_len = penalty_bytes_len;
+					}
+					else {
+						best_penalty_bytes_len = 0;
+					}
+				} else {
+					if (DEBUG_MODE) {
+					printf("Not enough identical recompressed bytes\n");
+					}
+				}
               }
             }
 }