[shiftingleft]

Shouldn't your snippet be using lzcnt? I can't see how this would result in the desired lookup.

for Zen5 rustc creates the following:

  utf8_sequence_length_lookup:
    shl edi, 24
    mov ecx, 274945
    not edi
    lzcnt eax, edi
    shl al, 2
    shrx rax, rcx, rax
    and al, 7
    ret

https://rust.godbolt.org/z/hz1eKjnaG

[Cold_Miserable]

I can't see any elegant solution. \n

Struggling proc \n lzcnt ecx,ecx \n test cl,cl \n setz al \n lea edx,[ecx-2] ;[0,1,2] \n cmp rdx,2 \n cmovle eax,ecx \n ret \n Struggling endp

[userbinator]

and the leading count comes in cl

We can assume the count has already been done.

[shiftingleft]

Ah I can't read, thanks :-)