const CODES: [(u32, u8); 257] = [
(0x1ff8, 13),
(0x7fffd8, 23),
(0xfffffe2, 28),
(0xfffffe3, 28),
(0xfffffe4, 28),
(0xfffffe5, 28),
(0xfffffe6, 28),
(0xfffffe7, 28),
(0xfffffe8, 28),
(0xffffea, 24),
(0x3ffffffc, 30),
(0xfffffe9, 28),
(0xfffffea, 28),
(0x3ffffffd, 30),
(0xfffffeb, 28),
(0xfffffec, 28),
(0xfffffed, 28),
(0xfffffee, 28),
(0xfffffef, 28),
(0xffffff0, 28),
(0xffffff1, 28),
(0xffffff2, 28),
(0x3ffffffe, 30),
(0xffffff3, 28),
(0xffffff4, 28),
(0xffffff5, 28),
(0xffffff6, 28),
(0xffffff7, 28),
(0xffffff8, 28),
(0xffffff9, 28),
(0xffffffa, 28),
(0xffffffb, 28),
(0x14, 6),
(0x3f8, 10),
(0x3f9, 10),
(0xffa, 12),
(0x1ff9, 13),
(0x15, 6),
(0xf8, 8),
(0x7fa, 11),
(0x3fa, 10),
(0x3fb, 10),
(0xf9, 8),
(0x7fb, 11),
(0xfa, 8),
(0x16, 6),
(0x17, 6),
(0x18, 6),
(0x0, 5),
(0x1, 5),
(0x2, 5),
(0x19, 6),
(0x1a, 6),
(0x1b, 6),
(0x1c, 6),
(0x1d, 6),
(0x1e, 6),
(0x1f, 6),
(0x5c, 7),
(0xfb, 8),
(0x7ffc, 15),
(0x20, 6),
(0xffb, 12),
(0x3fc, 10),
(0x1ffa, 13),
(0x21, 6),
(0x5d, 7),
(0x5e, 7),
(0x5f, 7),
(0x60, 7),
(0x61, 7),
(0x62, 7),
(0x63, 7),
(0x64, 7),
(0x65, 7),
(0x66, 7),
(0x67, 7),
(0x68, 7),
(0x69, 7),
(0x6a, 7),
(0x6b, 7),
(0x6c, 7),
(0x6d, 7),
(0x6e, 7),
(0x6f, 7),
(0x70, 7),
(0x71, 7),
(0x72, 7),
(0xfc, 8),
(0x73, 7),
(0xfd, 8),
(0x1ffb, 13),
(0x7fff0, 19),
(0x1ffc, 13),
(0x3ffc, 14),
(0x22, 6),
(0x7ffd, 15),
(0x3, 5),
(0x23, 6),
(0x4, 5),
(0x24, 6),
(0x5, 5),
(0x25, 6),
(0x26, 6),
(0x27, 6),
(0x6, 5),
(0x74, 7),
(0x75, 7),
(0x28, 6),
(0x29, 6),
(0x2a, 6),
(0x7, 5),
(0x2b, 6),
(0x76, 7),
(0x2c, 6),
(0x8, 5),
(0x9, 5),
(0x2d, 6),
(0x77, 7),
(0x78, 7),
(0x79, 7),
(0x7a, 7),
(0x7b, 7),
(0x7ffe, 15),
(0x7fc, 11),
(0x3ffd, 14),
(0x1ffd, 13),
(0xffffffc, 28),
(0xfffe6, 20),
(0x3fffd2, 22),
(0xfffe7, 20),
(0xfffe8, 20),
(0x3fffd3, 22),
(0x3fffd4, 22),
(0x3fffd5, 22),
(0x7fffd9, 23),
(0x3fffd6, 22),
(0x7fffda, 23),
(0x7fffdb, 23),
(0x7fffdc, 23),
(0x7fffdd, 23),
(0x7fffde, 23),
(0xffffeb, 24),
(0x7fffdf, 23),
(0xffffec, 24),
(0xffffed, 24),
(0x3fffd7, 22),
(0x7fffe0, 23),
(0xffffee, 24),
(0x7fffe1, 23),
(0x7fffe2, 23),
(0x7fffe3, 23),
(0x7fffe4, 23),
(0x1fffdc, 21),
(0x3fffd8, 22),
(0x7fffe5, 23),
(0x3fffd9, 22),
(0x7fffe6, 23),
(0x7fffe7, 23),
(0xffffef, 24),
(0x3fffda, 22),
(0x1fffdd, 21),
(0xfffe9, 20),
(0x3fffdb, 22),
(0x3fffdc, 22),
(0x7fffe8, 23),
(0x7fffe9, 23),
(0x1fffde, 21),
(0x7fffea, 23),
(0x3fffdd, 22),
(0x3fffde, 22),
(0xfffff0, 24),
(0x1fffdf, 21),
(0x3fffdf, 22),
(0x7fffeb, 23),
(0x7fffec, 23),
(0x1fffe0, 21),
(0x1fffe1, 21),
(0x3fffe0, 22),
(0x1fffe2, 21),
(0x7fffed, 23),
(0x3fffe1, 22),
(0x7fffee, 23),
(0x7fffef, 23),
(0xfffea, 20),
(0x3fffe2, 22),
(0x3fffe3, 22),
(0x3fffe4, 22),
(0x7ffff0, 23),
(0x3fffe5, 22),
(0x3fffe6, 22),
(0x7ffff1, 23),
(0x3ffffe0, 26),
(0x3ffffe1, 26),
(0xfffeb, 20),
(0x7fff1, 19),
(0x3fffe7, 22),
(0x7ffff2, 23),
(0x3fffe8, 22),
(0x1ffffec, 25),
(0x3ffffe2, 26),
(0x3ffffe3, 26),
(0x3ffffe4, 26),
(0x7ffffde, 27),
(0x7ffffdf, 27),
(0x3ffffe5, 26),
(0xfffff1, 24),
(0x1ffffed, 25),
(0x7fff2, 19),
(0x1fffe3, 21),
(0x3ffffe6, 26),
(0x7ffffe0, 27),
(0x7ffffe1, 27),
(0x3ffffe7, 26),
(0x7ffffe2, 27),
(0xfffff2, 24),
(0x1fffe4, 21),
(0x1fffe5, 21),
(0x3ffffe8, 26),
(0x3ffffe9, 26),
(0xffffffd, 28),
(0x7ffffe3, 27),
(0x7ffffe4, 27),
(0x7ffffe5, 27),
(0xfffec, 20),
(0xfffff3, 24),
(0xfffed, 20),
(0x1fffe6, 21),
(0x3fffe9, 22),
(0x1fffe7, 21),
(0x1fffe8, 21),
(0x7ffff3, 23),
(0x3fffea, 22),
(0x3fffeb, 22),
(0x1ffffee, 25),
(0x1ffffef, 25),
(0xfffff4, 24),
(0xfffff5, 24),
(0x3ffffea, 26),
(0x7ffff4, 23),
(0x3ffffeb, 26),
(0x7ffffe6, 27),
(0x3ffffec, 26),
(0x3ffffed, 26),
(0x7ffffe7, 27),
(0x7ffffe8, 27),
(0x7ffffe9, 27),
(0x7ffffea, 27),
(0x7ffffeb, 27),
(0xffffffe, 28),
(0x7ffffec, 27),
(0x7ffffed, 27),
(0x7ffffee, 27),
(0x7ffffef, 27),
(0x7fffff0, 27),
(0x3ffffee, 26),
(0x3fffffff, 30),
];
#[derive(Clone, Copy, Debug, Eq, PartialEq)]
pub(crate) enum EncodeError {
BitLengthOverflow,
ByteLengthOverflow,
}
#[derive(Clone, Copy, Debug, Eq, PartialEq)]
pub(crate) enum DecodeError {
EosSymbol,
InvalidHuffmanCode,
InvalidPadding,
DecodedLengthOverflow,
}
pub(crate) fn encoded_len(decoded: &[u8]) -> Result<usize, EncodeError> {
let mut bits = 0usize;
for &byte in decoded {
bits = bits
.checked_add(usize::from(CODES[usize::from(byte)].1))
.ok_or(EncodeError::BitLengthOverflow)?;
}
bits.checked_add(7)
.ok_or(EncodeError::ByteLengthOverflow)
.map(|bits| bits / 8)
}
pub(crate) fn encode_prevalidated(decoded: &[u8], destination: &mut [u8]) {
let mut pending = 0u64;
let mut pending_bits = 0u8;
let mut output = 0usize;
for &byte in decoded {
let (code, code_bits) = CODES[usize::from(byte)];
pending = (pending << code_bits) | u64::from(code);
pending_bits += code_bits;
while pending_bits >= 8 {
pending_bits -= 8;
destination[output] = (pending >> pending_bits) as u8;
output += 1;
pending &= (1u64 << pending_bits) - 1;
}
}
if pending_bits != 0 {
destination[output] =
((pending << (8 - pending_bits)) | ((1u64 << (8 - pending_bits)) - 1)) as u8;
}
}
pub(crate) fn decoded_len(encoded: &[u8]) -> Result<usize, DecodeError> {
let mut code = 0u32;
let mut bits = 0u8;
let mut length = 0usize;
for byte in encoded {
for shift in (0..8).rev() {
code = (code << 1) | u32::from((byte >> shift) & 1);
bits += 1;
if let Some(symbol) = symbol_for(code, bits) {
if symbol == 256 {
return Err(DecodeError::EosSymbol);
}
length = length
.checked_add(1)
.ok_or(DecodeError::DecodedLengthOverflow)?;
code = 0;
bits = 0;
} else if !is_prefix(code, bits) {
return Err(DecodeError::InvalidHuffmanCode);
}
}
}
validate_tail(code, bits)?;
Ok(length)
}
pub(crate) fn decode_prevalidated(encoded: &[u8], destination: &mut [u8]) {
let mut code = 0u32;
let mut bits = 0u8;
let mut output = 0usize;
for byte in encoded {
for shift in (0..8).rev() {
code = (code << 1) | u32::from((byte >> shift) & 1);
bits += 1;
if let Some(symbol) = symbol_for(code, bits) {
if symbol != 256 {
destination[output] = symbol as u8;
output += 1;
}
code = 0;
bits = 0;
}
}
}
}
fn symbol_for(code: u32, bits: u8) -> Option<usize> {
CODES
.iter()
.position(|&(candidate, candidate_bits)| candidate_bits == bits && candidate == code)
}
fn is_prefix(code: u32, bits: u8) -> bool {
CODES.iter().any(|&(candidate, candidate_bits)| {
candidate_bits > bits && (candidate >> (candidate_bits - bits)) == code
})
}
fn validate_tail(code: u32, bits: u8) -> Result<(), DecodeError> {
if bits == 0 {
return Ok(());
}
if bits > 7 || code != (1u32 << bits) - 1 {
return Err(DecodeError::InvalidPadding);
}
Ok(())
}