Have you considered simply using the checksum feature of unpack itself?

In addition to fields allowed in pack(), you may prefix a field with a %<number> to indicate that you want a <number>-bit checksum of the items instead of the items themselves. Default is a 16-bit checksum. Checksum is calculated by summing numeric values of expanded values (for string fields the sum of "ord($char)" is taken, for bit fields the sum of zeroes and ones).
Or, if that isn't what you're trying to accomplish, what about Digest::MD5 or Digest::Adler32?

In reply to Re: Difficulty producing correct checksum by jrsimmon
in thread Difficulty producing correct checksum by Anonymous Monk

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