Replacing if statements with ternary operators doesn't make the code branchless. It's just different syntax.

Correct, although the new code is more elegant I believe. No?

The PR removed a branch later on by always printing two digits (a common convention). So this removes a branch in some cases and might be faster.

The branchless here means no jmp or other branch instruction in assembly code, using comv instead.
So the ternary operators is just a easy way for compiler to generate comv, the clang generated assembly code is

        mov     ecx, esi
        neg     ecx
        cmovs   ecx, esi
        shr     esi, 31
        add     sil, sil
        add     sil, 43
        mov     byte ptr [rdi], sil

But I have to say, even with or without ternary operator, the compiler still generate the same assembly code, see here

@taoliq Yes. But the reason for it is due to how the code is written. In both branches in the old code, we do much the same work... so that the compiler can recognize the pattern and optimize accordingly.