use generic to allow 32 and 64 uint keys #30
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Feel free to squash commits. |
| // lemire.me/blog/2016/06/27/a-fast-alternative-to-the-modulo-reduction/ | ||
| func fastModN(x, n uint32) uint32 { | ||
| return uint32((uint64(x) * uint64(n)) >> 32) | ||
| func fastModN[S constraints.Unsigned](x, n S) S { | ||
| return S((uint64(x) * uint64(n)) >> 32) |
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This is the part that will not work with uint64: it will always return values in 32-bit range, so those buckets will be unused.
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I see. Would returning unsafe.Sizeof(S) help here? Or is this a bit-op trick that can not be rescued?
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I don't think it can be rescued without having to do the usual modulo division. See the link above that explains how the trick works.
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This writeup shows a possible version to support uint64 ranges.
Perhaps there's a method here for assigning the correct fastmodN for the map instantiation. It, however, wouldn't be inlined by the compiler.
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Thank you for the link! It's always great to learn something new.
Maybe it would make sense to just have a fork of this repo (swiss64?) with the 64-bit version? It should be quite easy to keep it up to date (I guess there shouldn't be many or frequent incoming changes), the API would be clean (swiss.Map vs swiss64.Map) and the code would be easier and faster to follow. WDYT?
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I'm not sure. That seems like a dolthub call.
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the fast modulo with 64 bits support can be as simple as
func fastModN(x, n uint) uint {
h, _ := bits.Mul(x, n)
return h
}but this requires the high bits of x to be set (which is not necessarily the case for H1, depending on implementation). So just call it with x=H1<<7
Edit: and the compiler inlines it.
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Um... go 1.24 is getting native support for swiss tables. I assume this will be resolved already. Closing in favor of that. |
#27