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Hello @Ratio2, can you elaborate a bit more on what this PR is doing to improve performance?

Hello @Ratio2, can you elaborate a bit more on what this PR is doing to improve performance?

Input data:
func combineIndexes(from []*MatchmakerIndex, min, max int)
len(from) = 32
min = 2
max = 2

The function call duration is 118 seconds, since we have complexity O(N*2^N) from the input array size regardless of min/max. The loop for combinationBits := 1; combinationBits < (1 << length); combinationBits++ consists of 2^32 iterations, which is a lot, and there is also an inner loop for element := uint(0); element < length; element++.

The main idea of ​​the change is to not iterate over impossible combinations in the loop. If max = 2, then we are not interested in combinations of 3 or more elements.

iterium.Combinations generates all possible combinations of N elements.
rangeCombinations generates all possible combinations of 1..N elements. If the input is [a, b, c], then the output is [[a], [a, b], [a, c], [b], [b, c], [c]].