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    SubjectRe: [RFC][PATCH] Faster generic_fls
    Linus Torvalds <> writes:

    > Clearly you're not going to make _one_ load to get fls, since having
    > a 4GB lookup array for a 32-bit fls would be "somewhat" wasteful.
    > So the lookup table would probably look up just the last 8 bits.
    > So the lookup table version is several instructions in itself, doing
    > about half of what the calculating version needs to do _anyway_.


    > Including those data-dependent branches.

    Well, at least on Alpha, gcc can optimize them all away except one.

    Note I'm not really arguing Linux should use a lookup table for fls;
    I'm just arguing putting it as default into libgcc for architectures
    that don't provide a special version (which aren't particularly many)
    isn't stupid. But probably I'm just biased, because I put it there :)

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