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  • Once you've done the hash, you've already read the whole file. Why do it again? Commented Aug 24, 2012 at 21:22
  • @ZaidMasud The hash could be stored though. Commented Aug 24, 2012 at 21:22
  • Depending on the number of comparisons the chance of a collision in a hash (even MD5 which is not cryptographically secure) can be unacceptably high. For an explanation -- here is a link blog.mischel.com/2012/04/13/hash-codes-are-not-unique Commented Aug 24, 2012 at 21:30
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    @jtm001 as a quick-to-false, cryptographic security is irrelevant and the necessary collision safety just has to be enough that false collisions don't cause more unnecessary checks than they prevent, which even CRC would be likely to be enough for. Commented Aug 24, 2012 at 21:38
  • @JonHanna -- agreed completely -- the point was intended to address the comment "not 100% match the two files with the same hash Are you sure?" Commented Aug 24, 2012 at 21:41