WIP: Use size check to quickly reject unequal files #3
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In multiple-mode, it can be much faster to first verify that the files cannot be equal by checking if their sizes don't match. In that case, it makes no sense to compute a hash for potentially large files. Also, by checking size first, we ensure that if the hashes match, they must also agree on file size as well (a much stronger assurance for equivalency of the crypto-hashed files).
chadnetzer
changed the title
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Worth postponing for a bit until after PR#5 (or similar) fix is applied. |
The hash computations use MaxSize as a to limit their work, such as if given a device file with unbounded I/O (ie. /dev/zero). The default value of zero should be set before getHash attempts to compute a hash, so that the hash input is not truncated to zero. Rather than special handling for character devices, it may be preferable for such cases to use CompareReader(). For example, what should the expected result be for comparing /dev/zero to a 1K file file of all zeros? If MaxSize is not set, or set to > 1K, probably they should not match. And if MaxSize is set to zero, probably they should match. However, Stat() will return size 0 for /dev/zero (and other character device files), so arguably CompareFiles() is not well defined on character device files (and that's just for Unix).
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Good, thanks! |
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In multiple-mode, it can be much faster to first verify that the files cannot be equal by checking if their sizes don't match. In that case, it makes no sense to compute a hash for potentially large files.
Also, by checking size first, we ensure that if the hashes match, they must also agree on file size as well (a much stronger assurance for equivalency of the crypto-hashed files).