Word size in `noise`

[jedisct1]

On an AMD Zen2 CPU:

https://github.com/bwesterb/kyber-zig/blob/da1ab9f5a9c5fce24dba5e7e165c86f51727252a/src/main.zig#L1139

• u64:

         kyber512:      60885 encaps/s
         kyber768:      40204 encaps/s
        kyber1024:      29370 encaps/s

• u128:

         kyber512:      62503 encaps/s
         kyber768:      43465 encaps/s
        kyber1024:      31931 encaps/s

• u32:

         kyber512:      71386 encaps/s
         kyber768:      51741 encaps/s
        kyber1024:      38671 encaps/s

u32 is actually faster, probably due to better opportunities for auto vectorization.

[bwesterb]

On M2 Pro:

• u32

       kyber512:      49431 encaps/s
       kyber768:      46900 encaps/s
      kyber1024:      40496 encaps/s
       kyber512:      93939 decaps/s
       kyber768:      66015 decaps/s
      kyber1024:      48002 decaps/s
       kyber512:      76156 keygen/s
       kyber768:      43677 keygen/s
      kyber1024:      26951 keygen/s

• u64

       kyber512:      49892 encaps/s
       kyber768:      47831 encaps/s
      kyber1024:      41748 encaps/s
       kyber512:      91408 decaps/s
       kyber768:      63460 decaps/s
      kyber1024:      48021 decaps/s
       kyber512:      72777 keygen/s
       kyber768:      43475 keygen/s
      kyber1024:      26621 keygen/s

• u128

       kyber512:      54565 encaps/s
       kyber768:      47450 encaps/s
      kyber1024:      41330 encaps/s
       kyber512:      92113 decaps/s
       kyber768:      63905 decaps/s
      kyber1024:      46823 decaps/s
       kyber512:      74247 keygen/s
       kyber768:      43298 keygen/s
      kyber1024:      26958 keygen/s

[bwesterb]

Cool that it's so easy to check this. It'd be quite a bit of work with the C reference implementation.