Challenge: write a really really small front() for UTF8

[Michel Fortin]

On 2014-03-23 21:22:58 +0000, Andrei Alexandrescu 
<SeeWebsiteForEmail at erdani.org> said:

> Here's a baseline: http://goo.gl/91vIGc. Destroy!

Optimizing for smallest assembly size:

dchar front(char[] s)
{
  size_t bytesize;
  dchar result;
  switch (s[0])
  {
    case 0b00000000: .. case 0b01111111:
    	return s[0];
    case 0b11000000: .. case 0b11011111:
    	return ((s[0] & 0b00011111) << 6) | (s[1] & 0b00011111);
    case 0b11100000: .. case 0b11101111:
    	result = s[0] & 0b00001111;
    	bytesize = 3;
    	break;
    case 0b11110000: .. case 0b11110111:
    	result = s[0] & 0b00000111;
    	bytesize = 4;
    default:
       return dchar.init;
  }
  foreach (i; 1..bytesize)
      result = (result << 6) | (s[i] & 0b00111111);
  return result;
}

-- 
Michel Fortin
michel.fortin at michelf.ca
http://michelf.ca