Circular shifts about randomnumbers.jl HOT 11 CLOSED

This seems to work as desired on 0.5 (with -O3), but not on 0.4

function rotr(x,y)
    s = sizeof(x) << 3
    (x >> (y % s)) | (x << (-y % s))
end

from randomnumbers.jl.

Thanks, Simon. The former one seems very nice, I'll use this.

BTW there's a typo in the codes that it should be %4 = sub i64 63, %1

from randomnumbers.jl.

Why would it be 63, not 64?

from randomnumbers.jl.

I would suggest the latter one: the generality is well worth it, and hopefully 0.5 should be released by the time we're performance tuning. llvmcall is usually the last resort sort of thing.

from randomnumbers.jl.

Oh I just found myself wrong.

Okay, it's reasonable to take the second function.

from randomnumbers.jl.

Yesterday did you mean that I should just write

@inline function pcg_rotr(x::UIntTypes, y::UIntTypes)
    s = sizeof(x) << 3
    (x >> (y % s)) | (x << (-y % s))
end

instead of the current @eval form?

from randomnumbers.jl.

Yes, exactly: @eval gets you nothing in this case (each combination of concrete UInt types will still be JIT-ed).

You could even do this for a lot of the other functions, as it seems like the constants can mostly be computed (and so will be evaluated at compile time).

from randomnumbers.jl.

e.g. for XSH RR, you could include in the function

    s = sizeof(state) << 3
    t = trailing_zeros(s)-1 # log2(s)-1
    p1 = (s>>1 + t)>>1
    p2 = s>>1 - t
    p3 = s-t

which the JIT is smart enough to evaluate as constants.

from randomnumbers.jl.

Though for 128 bits, this gives a p1 as 35, not 29 as in your code: where did you get the constants from?

from randomnumbers.jl.

I copied the constants in the PCG sources. http://www.pcg-random.org/download.html

from randomnumbers.jl.

Ah, I see. I opened an issue here:
imneme/pcg-c-basic#7

I guess we see what the author says.

from randomnumbers.jl.