Implementing variadic min / max functions

Question

I\'m implementing variadic min/max functions. A goal is to take advantage of the compile time known number of arguments and perform an unrolled evaluation (

Answer 1

There is a solution in C++17 which beats all answers proposed so far:

template 
constexpr auto min(Head0 &&head0, Head1 &&head1, Tail &&... tail)
{
    if constexpr (sizeof...(tail) == 0) {
        return head0 < head1 ? head0 : head1;
    }
    else {
        return min(min(head0, head1), tail...);
    }
}

Notice how this:

• requires only one function
• you can't call this with fewer than two parameters
• it compiles optimally

Using gcc 10.2 with -O3, the accepted answer compiles to:

min(int, int, int):
        cmp     esi, edi
        jge     .L2
        cmp     esi, edx
        mov     eax, edx
        cmovle  eax, esi
        ret
.L2:
        cmp     edi, edx
        mov     eax, edx
        cmovle  eax, edi
        ret

There are more instructions and a conditional jump for whatever reason. My solution compiles only to:

min(int, int, int):
        cmp     esi, edx
        mov     eax, edi
        cmovg   esi, edx
        cmp     esi, edi
        cmovle  eax, esi
        ret

This is identical to just calling std::min recursively for three parameters. (see https://godbolt.org/z/snavK5)