Can you shrink it further?

[safety0ff via Digitalmars-d]

My current favorites:

void popFront(ref char[] s) @trusted pure nothrow {
   immutable byte c = s[0];
   if (c >= -2) {
     s = s.ptr[1 .. s.length];
   } else {
     import core.bitop;
     size_t i = 7u - bsr(~c);
     import std.algorithm;
     s = s.ptr[min(i, s.length) .. s.length];
   }
}

I also experimented with explicit speculation:

void popFront(ref char[] s) @trusted pure nothrow {
   immutable byte c = s[0];
   s = s.ptr[1 .. s.length];
   if (c < -2) {
     import core.bitop;
     size_t i = 6u - bsr(~c);
     import std.algorithm;
     s = s.ptr[min(i, s.length) .. s.length];
   }
}


LDC and GDC both compile these to 23 instructions.
DMD does worse than with my other code.

You can influence GDC's block layout with __builtin_expect.

I notice that many other snippets posted use uint instead of 
size_t in the multi-byte branch. This generates extra 
instructions for me.