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

[Andrei Alexandrescu]

On 3/23/14, 6:53 PM, Michel Fortin wrote:
On 2014-03-23 21:22:58 +0000, Andrei Alexandrescu
<seewebsiteforem...@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;
}


Nice, thanks! I'd hope for a short path for the ASCII subset, could you 
achieve that?

Andrei