src/vendor/utf8-ranges-0.1.3/src/char_utf8.rs

   1 // Pulled from std::char until encode_utf8 stabilizes. ---AG
   2
   3 // UTF-8 ranges and tags for encoding characters
   4 const TAG_CONT: u8    = 0b1000_0000;
   5 const TAG_TWO_B: u8   = 0b1100_0000;
   6 const TAG_THREE_B: u8 = 0b1110_0000;
   7 const TAG_FOUR_B: u8  = 0b1111_0000;
   8 const MAX_ONE_B: u32   =     0x80;
   9 const MAX_TWO_B: u32   =    0x800;
  10 const MAX_THREE_B: u32 =  0x10000;
  11
  12 #[inline]
  13 pub fn encode_utf8(character: char, dst: &mut [u8]) -> Option<usize> {
  14     let code = character as u32;
  15     if code < MAX_ONE_B && !dst.is_empty() {
  16         dst[0] = code as u8;
  17         Some(1)
  18     } else if code < MAX_TWO_B && dst.len() >= 2 {
  19         dst[0] = (code >> 6 & 0x1F) as u8 | TAG_TWO_B;
  20         dst[1] = (code & 0x3F) as u8 | TAG_CONT;
  21         Some(2)
  22     } else if code < MAX_THREE_B && dst.len() >= 3  {
  23         dst[0] = (code >> 12 & 0x0F) as u8 | TAG_THREE_B;
  24         dst[1] = (code >>  6 & 0x3F) as u8 | TAG_CONT;
  25         dst[2] = (code & 0x3F) as u8 | TAG_CONT;
  26         Some(3)
  27     } else if dst.len() >= 4 {
  28         dst[0] = (code >> 18 & 0x07) as u8 | TAG_FOUR_B;
  29         dst[1] = (code >> 12 & 0x3F) as u8 | TAG_CONT;
  30         dst[2] = (code >>  6 & 0x3F) as u8 | TAG_CONT;
  31         dst[3] = (code & 0x3F) as u8 | TAG_CONT;
  32         Some(4)
  33     } else {
  34         None
  35     }
  36 }