[jdcarter]

I took that and check out what Clang does with 32-bit ints:

https://godbolt.org/g/ORsX5h

vs. what it does with 64-bit ints:

https://godbolt.org/g/2wBzn3

Can anybody explain the 32 bit version?

[CorvusCrypto]

It's just vectorizing calculations so that it's faster than pure iterative calculation. 64 bit version doesn't get this probably because that optimizer isn't SSE2 aware yet (just a guess I actually don't know) and can't do SIMD arithmetic with 2 64 bit floats

[user2994cb]

Harder to vectorize 64-bit arithmetic?

[CorvusCrypto]

was going to say this. It probably only does SSE and not SSE2. Therefore vectorization only happens for 32 bit ints.

[user2994cb]

Seems to need -mavx2 to really go to town with 64 bit: https://godbolt.org/g/6EFYeY

[jdcarter]

Thank you both, I appreciate the insight!