[boost] Re: A question about static_log2

[Vesa Karvonen]

Gennaro Prota:

Vesa Karvonen:

Gennaro Prota:

Vesa, I really appreciate your attempt but your code assumes the
required number to be a power of two (it just tries 32, 64, 128,
etc.). What about 48 bits unsigned long?[...]

If unsigned long has 48 bits, then an n of 32 would be chosen.

And then you are not able to calculate log2 for numbers in the range
[2**32, 2**48-1[ (at least).

The algorithm calculates log2 correctly even for those numbers. The invariant of the core algorithm is that at the start of each recursion 1 <= x && x>>n < 1ul<<n.

Regards,
Vesa Karvonen


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