Allow to set the minimum required match length.

The minimum required match length plays an important role in the
current algorithm. This algorithm requires that the current match
has at least 8 mismatches over a region where we find a new match,
therefore imposing a minimum match length of at least 8 bytes.
This patch allows to increase this minium value to avoid using small
matches that only match a very small region. A larger value can
improve the patch size, depending on the data, but a too large value
will cause the algorithm to miss matches that were otherwise benefical.

Bug: 73107113
Test: Added unittests. Ran it with different minlen values.

Change-Id: Iac594fc1cd7ecd5cfdc676bdb6ebe7c626de6dcd

1 files changed, 17 insertions, 0 deletions

diff --git a/include/bsdiff/bsdiff.h b/include/bsdiff/bsdiff.h
index 08cb688..b6475f4 100644
--- a/include/bsdiff/bsdiff.h
+++ b/include/bsdiff/bsdiff.h
@@ -34,6 +34,23 @@ int bsdiff(const uint8_t* old_buf,
            PatchWriterInterface* patch,
            SuffixArrayIndexInterface** sai_cache);
 
+// The |min_length| parameter determines the required minimum length of a match
+// to be considered instead of emitting mismatches. The minimum value is 9,
+// since smaller matches are always ignored. If a smaller value is passed, the
+// minimum value of 9 will be used instead. A very large value (past 30) will
+// give increasingly bad results as you increase the minimum length since legit
+// matches between the old and new data will be ignored. The exact best value
+// depends on the data, but the sweet spot should be between 9 and 20 for the
+// examples tested.
+BSDIFF_EXPORT
+int bsdiff(const uint8_t* old_buf,
+           size_t oldsize,
+           const uint8_t* new_buf,
+           size_t newsize,
+           size_t min_length,
+           PatchWriterInterface* patch,
+           SuffixArrayIndexInterface** sai_cache);
+
 }  // namespace bsdiff
 
 #endif  // _BSDIFF_BSDIFF_H_