A small change doubled the performance:

HV* countColors2( SV *img ) {
    STRLEN l;
    U32 *rgba = (U32*)SvPVx( img, l ), i;
    HV* counts = newHV();

    l /= 4;
    for( i = 0; i < l; ++i ) {
        SV **val;
        if( val = hv_fetch( counts, (char*)&rgba[ i ], 4, 0 ) ) {
            SvIV_set( *val, SvIV( *val ) + 1 );
        }
        else {
            SV *val = newSViv( 1 );
            hv_store( counts, (char*)&rgba[ i ], 4, val, 0 );
        }
    }
    return counts;
}

[download]
C:\test>1138218 mid.png
Width:12800 height:10240 pixels:131072000
Took 12.642578 seconds
Found 81814 colors in 131072000 pixels

[download]
With the rise and rise of 'Social' network sites: 'Computers are making people easier to use everyday'
Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
"Science is about questioning the status quo. Questioning authority". I knew I was on the right track :)
In the absence of evidence, opinion is indistinguishable from prejudice.
I'm with torvalds on this Agile (and TDD) debunked I told'em LLVM was the way to go. But did they listen!

In reply to Re^2: Perl Hashes in C? (Twice as fast) by BrowserUk
in thread Perl Hashes in C? by BrianP

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