6 ms·

Author her. I didn't run benchmarks. I'm suspicious of micro-benchmarks and I don't have a context where I can try it against realistic data. Also, I just enjoy

• eru 4y ago
  Thanks for replying! It's definitely a nice write-up. You are right that micro-benchmarks are a bit suspicious, but they are better than nothing. Btw, have a look at https://godbolt.org/z/zMarEnYP5 https://godbolt.org/z/zMarEnYP5 to see what Clang come up with on her own. #include<stdint.h> uint64_t div(uint64_t nlz) { __builtin_assume(nlz <= 63); return (63 - nlz) / 7; } div: # @div xori a0, a0, 63 andi a1, a0, 255 li a2, 37 mul a1, a1, a2 srli a1, a1, 8 subw a0, a0, a1 slli a0, a0, 56 srli a0, a0, 57 add a0, a0, a1 srli a0, a0, 2 ret This uses Risc-V assembly. Just for fun. x86 is also fascinating. I haven't analysed it in detail. But it looks like Clang doesn't seem to mind multiplication.