What is the fastest hash algorithm to check if two files are equal?

Question

What is the fastest way to create a hash function which will be used to check if two files are equal?

Security is not very important.

Edit: I am sending a fi

Answer 1

For this type of application, Adler32 is probably the fastest algorithm, with a reasonable level of security. For bigger files, you may calculate multiple hash values, for example one per block of 5 Mb of the file, hence decreasing the chances of errors (i.e. of cases when the hashes are same yet the file content differ). Furthermore this multi-hash values setup may allow the calculation of the hash to be implemented in a multi-thread fashion.

Edit: (Following Steven Sudit's remark)
A word of caution if the files are small!
Adler32's "cryptographic" properties, or rather its weaknesses are well known particularly for short messages. For this reason the solution proposed should be avoided for files smaller than than a few kilobytes.
Never the less, in the question, the OP explicitly seeks a fast algorithm and waives concerns about security. Furthermore the quest for speed may plausibly imply that one is dealing with "big" files rather than small ones. In this context, Adler32, possibly applied in parallel for files chunks of say 5Mb remains a very valid answer. Alder32 is reputed for its simplicity and speed. Also, its reliability, while remaining lower than that of CRCs of the same length, is quite acceptable for messages over 4000 bytes.