SHA question

Avi Greenbury avismailinglistaccount at
Wed Jan 13 14:03:51 GMT 2010

Dermot wrote:
> 2010/1/13 Roger Burton West <roger at>:
> > You may want to be slightly cleverer about it - taking a SHAsum is
> > computationally expensive, and it's only worth doing if the files
> > have the same size.
> Unfortunately the size varies quite a bit.

You might've missed his point.

If two files are of different sizes, they cannot be identical. Getting
the size of a file is substantially cheaper than hashing it.

So you check all your filesizes, and need only hash those pairs or
groups that are all the same size.

Avi Greenbury

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