Can you shrink it further?

[Stefan Koch via Digitalmars-d]

On Wednesday, 12 October 2016 at 08:56:59 UTC, Matthias Bentrup 
wrote:
>
> Here are three branch-less variants that use the sign instead 
> of the carry bit.
>
> The last one is the fastest on my machine, although it mixes 
> the rare error case and the common 1-byte case into one branch.
>
> void popFront1(ref char[] s) @trusted pure nothrow {
>   immutable c = cast(byte)s[0];
>   if (c >= 0) {
>     s = s[1 .. $];
>   } else if (c < -8) {
>     uint i = 4 + (c + 64 >> 31) + (c + 32 >> 31) + (c + 16 >> 
> 31);
>     import std.algorithm;
>     s = s[min(i, $) .. $];
>   } else {
>     s = s[1 .. $];
>   }
> }
>
> void popFront1a(ref char[] s) @trusted pure nothrow {
>   immutable c = cast(byte)s[0];
>   if (c >= 0) {Three
>     s = s[1 .. $];
>   } else {
>     uint i = 1 + ((3 + (c + 64 >> 31) + (c + 32 >> 31) + (c + 
> 16 >> 31)) & (c + 8 >> 31));
>     import std.algorithm;
>     s = s[min(i, $) .. $];
>   }
> }
>
> void popFront1b(ref char[] s) @trusted pure nothrow {
>   immutable c = cast(byte)s[0];
>   if (c >= -8) {
>     s = s[1 .. $];
>   } else {
>     uint i = 4 + (c + 64 >> 31) + (c + 32 >> 31) + (c + 16 >> 
> 31);
>     import std.algorithm;
>     s = s[min(i, $) .. $];
>   }
> }

All three are slower than baseline, for my test-case.
What did you test it against.