Counting unique pixel values is the equivalent of sort | uniq. No hashing, no associative maps are necessary.

A good solution involves picking the most suitable sort algorithm and implementation. One might bucket by one color, then mergesort and count on the 32bit values. Anyway, 30 million items single-threaded — this ought to be ~1 sec job.

In reply to Re: Perl Hashes in C? (just sort) by Anonymous Monk
in thread Perl Hashes in C? by BrianP

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