This hash look up in calculateColorProfile is the slowest part of saving an image.

[Andre von Houck]

I have profiled nimPNG code saving with VTune and 45% of the time is spent on this line:

nimPNG/nimPNG.nim

Line 2358 in 676bca4

 if not tree.hasKey(p): 

This line is in calculateColorProfile ... should it just be computed once? It seems like a very slow operation with the hashing taking up most of the time. Is there a way to compute calculateColorProfile only once?

I used vTune with nim c -d:release --debugger:native to produce this.

[andri lim]

Thank you, I think I know what's wrong with the hash function.

[Andre von Houck]

Amazing improvement, from the hottest function:

To being almost nothing:

Amazing!

Now the hottest path is the compression which is expected: