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

[Andrei Alexandrescu]

On 3/23/14, 9:49 PM, Michel Fortin wrote:
>
> dchar front(char[] s)
> {
>   if (s[0] < 0b1000000)
>     return s[0]; // ASCII
>
>   // pattern     indicator  tailLength
>   // 0b1100xxxx  0b00 (0)   1
>   // 0b1101xxxx  0b01 (1)   1 == indicator
>   // 0b1110xxxx  0b10 (2)   2 == indicator
>   // 0b1111xxxx  0b11 (3)   3 == indicator
>   // note: undefined result for illegal 0b11111xxx case
>
>   auto indicator = (s[0] >> 4) & 0b11;
>   auto tailLength = indicator ? indicator : 1;
>
>   dchar result = s[0] & (0b00111111 >> tailLength);
>   foreach (i; 0..tailLength)
>       result = (result << 6) | (s[1+i] & 0b00111111);
>   return result;
> }

http://goo.gl/y9EVFr

Andrei