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Replace quadratic Reverse with quasilinear #8301

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Replace quadratic Reverse with quasilinear #8301

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15 changes: 12 additions & 3 deletions std/meta.d
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Original file line number Diff line number Diff line change
Expand Up @@ -559,9 +559,18 @@ template ReplaceAll(args...)
*/
template Reverse(args...)
{
alias Reverse = AliasSeq!();
static foreach_reverse (arg; args)
Reverse = AliasSeq!(Reverse, arg);
static if (args.length <= 8)
{
// This part is O(n * n) because it grows an array by front insertions
alias Reverse = AliasSeq!();
static foreach_reverse (arg; args)
Reverse = AliasSeq!(Reverse, arg);
}
else
{
// This part is O(n * log n) because it does O(n) work for n, n/2, n/4...
alias Reverse = AliasSeq!(Reverse!(args[$ / 2 .. $]), Reverse!(args[0 .. $ / 2]));
}
}

///
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