Re: Lua5 / poor performance

["Peter S. Housel" <housel@...>]

"Roberto Ierusalimschy" <roberto@inf.puc-rio.br> wrote:
> Any solution to this problem must change the way Lua hashes non-integer
> numbers. One particular solution is this:
>
[solution using type punning]
>
> This code is not very "religious", but it does the trick. (The
> performance for integer keys is not affected by this change.)

A more portable, and very fast, method of hashing floating-point numbers
might be:

1) Extract the manitssa and exponent using frexp() function.
2) Multiply the mantissa by (double) 2^(bits in a long - 1)
3) Truncate the multiplication result to a long
4) Hash this result with together with the exponent

-Peter-