Comparison Algorithms

Simple Comparison Algorithm

This algorithm compares file data byte-by-byte. It uses three types of blocks:

• Matched
• Different
• Not Found

If two bytes are the same in both files - they will be marked as Matched. Otherwise, they are marked as Different. If one file is larger than another, its excess part is marked as Not Found.

This algorithm is convenient if two files are almost equal and there were no data inserted or removed from them.

Difference Algorithm

This algorithm searches for matched, modified, inserted and removed blocks in both files:

• Matched blocks are blocks of equal data in both files.
• Inserted blocks are blocks of data inserted into the first file. They are marked only in the second file as they are missing in the first one.
• Removed blocks are blocks of data removed from the first file. They are marked only in the first file as they are missing in the second one.
• Modified blocks are blocks of completely different data.

This algorithm has a quality/performance tuning option, specified in the Compare Files Window. If set to “Normal”, it may operate faster, but less accurately, and if set to “Precise”, it may operate slower (sometimes much slower), but will be able to find more matches.

Starting from version 7.21, there is a second implementation of a difference algorithm (called "Difference Algorithm (alternate)"), which should provide more accurate results for closely related files.