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#![no_std]
#![deny(missing_docs)]
#![deny(clippy::all)]
use bit_field::BitField;
#[derive(Debug, Copy, Clone)]
pub enum Error {
BufferOverflow,
MultiByte,
}
type Result<T> = core::result::Result<T, Error>;
pub fn encode(input: &str, buffer: &mut [u16]) -> Result<usize> {
let buffer_size = buffer.len();
let mut i = 0;
encode_with(input, |ch| {
if i >= buffer_size {
Err(Error::BufferOverflow)
} else {
buffer[i] = ch;
i += 1;
Ok(())
}
})?;
Ok(i)
}
pub fn encode_with<F>(input: &str, mut output: F) -> Result<()>
where
F: FnMut(u16) -> Result<()>,
{
let bytes = input.as_bytes();
let len = bytes.len();
let mut i = 0;
while i < len {
let ch;
if bytes[i] & 0b1000_0000 == 0b0000_0000 {
ch = u16::from(bytes[i]);
i += 1;
} else if bytes[i] & 0b1110_0000 == 0b1100_0000 {
if i + 1 >= len {
unsafe { core::hint::unreachable_unchecked() }
}
let a = u16::from(bytes[i] & 0b0001_1111);
let b = u16::from(bytes[i + 1] & 0b0011_1111);
ch = a << 6 | b;
i += 2;
} else if bytes[i] & 0b1111_0000 == 0b1110_0000 {
if i + 2 >= len || i + 1 >= len {
unsafe { core::hint::unreachable_unchecked() }
}
let a = u16::from(bytes[i] & 0b0000_1111);
let b = u16::from(bytes[i + 1] & 0b0011_1111);
let c = u16::from(bytes[i + 2] & 0b0011_1111);
ch = a << 12 | b << 6 | c;
i += 3;
} else if bytes[i] & 0b1111_0000 == 0b1111_0000 {
return Err(Error::MultiByte);
} else {
unsafe { core::hint::unreachable_unchecked() }
}
output(ch)?;
}
Ok(())
}
pub fn decode_with<F>(input: &[u16], mut output: F) -> Result<usize>
where
F: FnMut(&[u8]) -> Result<()>,
{
let mut written = 0;
for ch in input.iter() {
if (0x000..0x0080).contains(ch) {
output(&[*ch as u8])?;
written += 1;
} else if (0x0080..0x0800).contains(ch) {
let first = 0b1100_0000 + ch.get_bits(6..11) as u8;
let last = 0b1000_0000 + ch.get_bits(0..6) as u8;
output(&[first, last])?;
written += 2;
} else {
let first = 0b1110_0000 + ch.get_bits(12..16) as u8;
let mid = 0b1000_0000 + ch.get_bits(6..12) as u8;
let last = 0b1000_0000 + ch.get_bits(0..6) as u8;
output(&[first, mid, last])?;
written += 3;
}
}
Ok(written)
}
pub fn decode(input: &[u16], output: &mut [u8]) -> Result<usize> {
let buffer_size = output.len();
let mut i = 0;
decode_with(input, |bytes| {
if bytes.len() == 1 {
if i >= buffer_size {
return Err(Error::BufferOverflow);
}
output[i] = bytes[0];
i += 1;
} else if bytes.len() == 2 {
if i + 1 >= buffer_size {
return Err(Error::BufferOverflow);
}
output[i] = bytes[0];
output[i + 1] = bytes[1];
i += 2;
} else if bytes.len() == 3 {
if i + 2 >= buffer_size {
return Err(Error::BufferOverflow);
}
output[i] = bytes[0];
output[i + 1] = bytes[1];
output[i + 2] = bytes[2];
i += 3;
} else {
unreachable!("More than three bytes per UCS-2 character.");
}
Ok(())
})
}
#[cfg(test)]
mod tests {
use super::*;
#[test]
fn encoding() {
let input = "őэ╋";
let mut buffer = [0u16; 3];
let result = encode(input, &mut buffer);
assert_eq!(result.unwrap(), 3);
assert_eq!(buffer[..], [0x0151, 0x044D, 0x254B]);
}
#[test]
fn decoding() {
let input = "$¢ह한";
let mut u16_buffer = [0u16; 4];
let result = encode(input, &mut u16_buffer);
assert_eq!(result.unwrap(), 4);
let mut u8_buffer = [0u8; 9];
let result = decode(&u16_buffer, &mut u8_buffer);
assert_eq!(result.unwrap(), 9);
assert_eq!(core::str::from_utf8(&u8_buffer[0..9]), Ok("$¢ह한"));
}
#[test]
fn decoding_with() {
let input = "$¢ह한";
let mut u16_buffer = [0u16; 4];
let result = encode(input, &mut u16_buffer);
assert_eq!(result.unwrap(), 4);
let mut u8_buffer = [0u8; 9];
let mut pos = 0;
let result = decode_with(&u16_buffer, |bytes| {
for byte in bytes.into_iter() {
u8_buffer[pos] = *byte;
pos += 1;
}
Ok(())
});
assert_eq!(result.unwrap(), 9);
assert_eq!(core::str::from_utf8(&u8_buffer[0..9]), Ok("$¢ह한"));
}
}