When perl is not quite fast enough

  in the original that the code is just concatenating the converted form of each byte together. So instead of making sprintf convert each value in turn, only for perl ops to stick them together, I use x to replicate the per-byte format string once for each byte I'm about to convert. There's now one "\\xX" for each of the numbers in the list passed from unpack to sprintf, so sprintf just does what it's told. And sprintf is faster than perl ops.

How to make perl fast enough

use the language's fast features

You have enormous power at your disposal with regexps, pack, unpack and sprintf. So why not use them?

All the pack and unpack code is implemented in pure C, so doesn't have any of the book-keeping overhead of perl ops. sprintf too is pure C, so it's fast. The regexp engine uses its own private bytecode, but it's specially tuned for regexps, so it runs much faster than general perl code. And the implementation of tr has less to do than the regexp engine, so it's faster.

For maximum power, remember that you can generate regexps and the formats for pack, unpack and sprintf at run time, based on your data.

give the interpreter hints

Make it obvious to the interpreter what you're up to. Avoid $&, use (?:...) when you don't need capturing, and put the /o flag on constant regexps.

less OPs

Try to accomplish your tasks using less operations. If you find you have to optimise an existing program then this is where to start - golf is good, but remember it's run time strokes not source code strokes.

less CPU

Usually you want to find ways of using less CPU.

less RAM

but don't forget to think about how your data structures work to see if you can make them use less RAM.

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