reduce nesting in blassertsplit

[thewilsonator]

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[thewilsonator]

the performance of this function is O(very bad), I want to refactor it a bit before making it O(acceptable)

[WalterBright]

I presume this is about https://issues.dlang.org/show_bug.cgi?id=19550

[thewilsonator]

Yes.

[WalterBright]

I put a link to this in 19550.

[thewilsonator]

N.B. this doesn't fix that issue, I'm just beautifying the code beforehand. I don't really understand the code other than that it does what appears to be an awful lot of nested looping.