in reply to Re^2: Count byte/character occurrence (1/4)
in thread Count byte/character occurrence (quickly)

would something with a for loop and substr be faster? I dont necessarily have to unpack any bytes, do I?

That requires a call into C (substr) for every byte; where using unpack requires a single call for the entire string.

The cardinal rule for optimising Perl code, is to get perl's built-ins to do as much of the work as you can.

Using this loop: 

    ++$seen[ ord chop $buf ] while length $buf;

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in place of the unpack loop is almost but not quite as fast.

It trades 2 built-in calls per byte, against the cost of building the unpack return list on the stack, and loses by a hair.

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