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+//! 16-bit Huffman compression and decompression.
+//! Huffman compression and decompression routines written
+//! by Christian Rouet for his PIZ image file format.
+// see https://github.com/AcademySoftwareFoundation/openexr/blob/88246d991e0318c043e6f584f7493da08a31f9f8/OpenEXR/IlmImf/ImfHuf.cpp
+
+use crate::math::RoundingMode;
+use crate::error::{Error, Result, UnitResult, u64_to_usize, u32_to_usize};
+use crate::io::Data;
+use std::{
+ cmp::Ordering,
+ collections::BinaryHeap,
+ io::{Cursor, Read, Write},
+};
+use std::convert::TryFrom;
+use smallvec::SmallVec;
+
+
+pub fn decompress(compressed: &[u8], expected_size: usize) -> Result<Vec<u16>> {
+ let mut remaining_compressed = compressed;
+
+ let min_code_index = usize::try_from(u32::read(&mut remaining_compressed)?)?;
+ let max_code_index_32 = u32::read(&mut remaining_compressed)?;
+ let _table_size = usize::try_from(u32::read(&mut remaining_compressed)?)?; // TODO check this and return Err?
+ let bit_count = usize::try_from(u32::read(&mut remaining_compressed)?)?;
+ let _skipped = u32::read(&mut remaining_compressed)?; // what is this
+
+ let max_code_index = usize::try_from(max_code_index_32).unwrap();
+ if min_code_index >= ENCODING_TABLE_SIZE || max_code_index >= ENCODING_TABLE_SIZE {
+ return Err(Error::invalid(INVALID_TABLE_SIZE));
+ }
+
+ if RoundingMode::Up.divide(bit_count, 8) > remaining_compressed.len() {
+ return Err(Error::invalid(NOT_ENOUGH_DATA));
+ }
+
+ let encoding_table = read_encoding_table(&mut remaining_compressed, min_code_index, max_code_index)?;
+ if bit_count > 8 * remaining_compressed.len() { return Err(Error::invalid(INVALID_BIT_COUNT)); }
+
+ let decoding_table = build_decoding_table(&encoding_table, min_code_index, max_code_index)?;
+
+ let result = decode_with_tables(
+ &encoding_table,
+ &decoding_table,
+ &remaining_compressed,
+ i32::try_from(bit_count)?,
+ max_code_index_32,
+ expected_size,
+ )?;
+
+ Ok(result)
+}
+
+pub fn compress(uncompressed: &[u16]) -> Result<Vec<u8>> {
+ if uncompressed.is_empty() { return Ok(vec![]); }
+
+ let mut frequencies = count_frequencies(uncompressed);
+ let (min_code_index, max_code_index) = build_encoding_table(&mut frequencies);
+
+ let mut result = Cursor::new(Vec::with_capacity(uncompressed.len()));
+ u32::write_slice(&mut result, &[0; 5])?; // we come back to these later after we know more about the compressed data
+
+ let table_start = result.position();
+ pack_encoding_table(
+ &frequencies,
+ min_code_index,
+ max_code_index,
+ &mut result,
+ )?;
+
+ let data_start = result.position();
+ let bit_count = encode_with_frequencies(
+ &frequencies,
+ uncompressed,
+ max_code_index,
+ &mut result
+ )?;
+
+ // write meta data after this
+ result.set_position(0);
+ let table_length = data_start - table_start;
+
+ u32::try_from(min_code_index)?.write(&mut result)?;
+ u32::try_from(max_code_index)?.write(&mut result)?;
+ u32::try_from(table_length)?.write(&mut result)?;
+ u32::try_from(bit_count)?.write(&mut result)?;
+ 0_u32.write(&mut result)?;
+
+ Ok(result.into_inner())
+}
+
+
+const ENCODE_BITS: u64 = 16; // literal (value) bit length
+const DECODE_BITS: u64 = 14; // decoding bit size (>= 8)
+
+const ENCODING_TABLE_SIZE: usize = ((1 << ENCODE_BITS) + 1) as usize;
+const DECODING_TABLE_SIZE: usize = (1 << DECODE_BITS) as usize;
+const DECODE_MASK: u64 = DECODING_TABLE_SIZE as u64 - 1;
+
+const SHORT_ZEROCODE_RUN: u64 = 59;
+const LONG_ZEROCODE_RUN: u64 = 63;
+const SHORTEST_LONG_RUN: u64 = 2 + LONG_ZEROCODE_RUN - SHORT_ZEROCODE_RUN;
+const LONGEST_LONG_RUN: u64 = 255 + SHORTEST_LONG_RUN;
+
+
+#[derive(Clone, Debug, Eq, PartialEq)]
+enum Code {
+ Empty,
+ Short(ShortCode),
+ Long(SmallVec<[u32; 2]>), // often 2, sometimes 4, rarely 8
+}
+
+#[derive(Clone, Debug, Eq, PartialEq)]
+struct ShortCode {
+ value: u32,
+ len: u8,
+}
+
+impl ShortCode {
+ #[inline] fn len(&self) -> u64 { u64::from(self.len) }
+}
+
+/// Decode (uncompress) n bits based on encoding & decoding tables:
+fn decode_with_tables(
+ encoding_table: &[u64],
+ decoding_table: &[Code],
+ mut input: &[u8],
+ input_bit_count: i32,
+ run_length_code: u32,
+ expected_output_size: usize,
+) -> Result<Vec<u16>>
+{
+ let mut output = Vec::with_capacity(expected_output_size);
+ let mut code_bits = 0_u64;
+ let mut code_bit_count = 0_u64;
+
+ while input.len() > 0 {
+ read_byte(&mut code_bits, &mut code_bit_count, &mut input)?;
+
+ // Access decoding table
+ while code_bit_count >= DECODE_BITS {
+ let code_index = (code_bits >> (code_bit_count - DECODE_BITS)) & DECODE_MASK;
+ let code = &decoding_table[u64_to_usize(code_index)];
+
+ // Get short code
+ if let Code::Short(code) = code {
+ code_bit_count -= code.len();
+
+ read_code_into_vec(
+ code.value,
+ run_length_code,
+ &mut code_bits,
+ &mut code_bit_count,
+ &mut input,
+ &mut output,
+ expected_output_size,
+ )?;
+ }
+ else if let Code::Long(ref long_codes) = code {
+ debug_assert_ne!(long_codes.len(), 0);
+
+ let long_code = long_codes.iter()
+ .filter_map(|&long_code|{
+ let encoded_long_code = encoding_table[u32_to_usize(long_code)];
+ let length = length(encoded_long_code);
+
+ while code_bit_count < length && input.len() > 0 {
+ let err = read_byte(&mut code_bits, &mut code_bit_count, &mut input);
+ if let Err(err) = err { return Some(Err(err)); }
+ }
+
+ if code_bit_count >= length {
+ let required_code = (code_bits >> (code_bit_count - length)) & ((1 << length) - 1);
+
+ if self::code(encoded_long_code) == required_code {
+ code_bit_count -= length;
+ return Some(Ok(long_code));
+ }
+ }
+
+ None
+
+ })
+ .next()
+ .ok_or(Error::invalid(INVALID_CODE))?;
+
+ read_code_into_vec(
+ long_code?,
+ run_length_code,
+ &mut code_bits,
+ &mut code_bit_count,
+ &mut input,
+ &mut output,
+ expected_output_size,
+ )?;
+ }
+ else {
+ return Err(Error::invalid(INVALID_CODE));
+ }
+ }
+ }
+
+ let count = u64::try_from((8 - input_bit_count) & 7)?;
+ code_bits >>= count;
+ code_bit_count -= count;
+
+ while code_bit_count > 0 {
+ let index = (code_bits << (DECODE_BITS - code_bit_count)) & DECODE_MASK;
+ let code = &decoding_table[u64_to_usize(index)];
+
+ if let Code::Short(short_code) = code {
+ if short_code.len() > code_bit_count { return Err(Error::invalid("code")) }; // FIXME why does this happen??
+ code_bit_count -= short_code.len(); // FIXME may throw "attempted to subtract with overflow"
+
+ read_code_into_vec(
+ short_code.value,
+ run_length_code,
+ &mut code_bits,
+ &mut code_bit_count,
+ &mut input,
+ &mut output,
+ expected_output_size,
+ )?;
+ }
+ else {
+ return Err(Error::invalid(INVALID_CODE));
+ }
+ }
+
+ if output.len() != expected_output_size {
+ return Err(Error::invalid(NOT_ENOUGH_DATA));
+ }
+
+ Ok(output)
+}
+
+/// Build a decoding hash table based on the encoding table code:
+/// - short codes (<= HUF_DECBITS) are resolved with a single table access;
+/// - long code entry allocations are not optimized, because long codes are
+/// unfrequent;
+/// - decoding tables are used by hufDecode();
+fn build_decoding_table(
+ encoding_table: &[u64],
+ min_code_index: usize,
+ max_code_index: usize,
+) -> Result<Vec<Code>>
+{
+ let mut decoding_table = vec![Code::Empty; DECODING_TABLE_SIZE]; // not an array because of code not being copy
+
+ for (code_index, &encoded_code) in encoding_table[..= max_code_index].iter().enumerate().skip(min_code_index) {
+ let code_index = u32::try_from(code_index).unwrap();
+
+ let code = code(encoded_code);
+ let length = length(encoded_code);
+
+ if code >> length != 0 {
+ return Err(Error::invalid(INVALID_TABLE_ENTRY));
+ }
+
+ if length > DECODE_BITS {
+ let long_code = &mut decoding_table[u64_to_usize(code >> (length - DECODE_BITS))];
+
+ match long_code {
+ Code::Empty => *long_code = Code::Long(smallvec![code_index]),
+ Code::Long(lits) => lits.push(code_index),
+ _ => { return Err(Error::invalid(INVALID_TABLE_ENTRY)); }
+ }
+ }
+ else if length != 0 {
+ let default_value = Code::Short(ShortCode {
+ value: code_index,
+ len: length as u8,
+ });
+
+ let start_index = u64_to_usize(code << (DECODE_BITS - length));
+ let count = u64_to_usize(1 << (DECODE_BITS - length));
+
+ for value in &mut decoding_table[start_index .. start_index + count] {
+ *value = default_value.clone();
+ }
+ }
+ }
+
+ Ok(decoding_table)
+}
+
+/// Run-length-decompresses all zero runs from the packed table to the encoding table
+fn read_encoding_table(
+ packed: &mut impl Read,
+ min_code_index: usize,
+ max_code_index: usize,
+) -> Result<Vec<u64>>
+{
+ let mut code_bits = 0_u64;
+ let mut code_bit_count = 0_u64;
+
+ // TODO push() into encoding table instead of index stuff?
+ let mut encoding_table = vec![0_u64; ENCODING_TABLE_SIZE];
+ let mut code_index = min_code_index;
+ while code_index <= max_code_index {
+ let code_len = read_bits(6, &mut code_bits, &mut code_bit_count, packed)?;
+ encoding_table[code_index] = code_len;
+
+ if code_len == LONG_ZEROCODE_RUN {
+ let zerun_bits = read_bits(8, &mut code_bits, &mut code_bit_count, packed)?;
+ let zerun = usize::try_from(zerun_bits + SHORTEST_LONG_RUN).unwrap();
+
+ if code_index + zerun > max_code_index + 1 {
+ return Err(Error::invalid(TABLE_TOO_LONG));
+ }
+
+ for value in &mut encoding_table[code_index..code_index + zerun] {
+ *value = 0;
+ }
+
+ code_index += zerun;
+ }
+ else if code_len >= SHORT_ZEROCODE_RUN {
+ let duplication_count = usize::try_from(code_len - SHORT_ZEROCODE_RUN + 2).unwrap();
+ if code_index + duplication_count > max_code_index + 1 {
+ return Err(Error::invalid(TABLE_TOO_LONG));
+ }
+
+ for value in &mut encoding_table[code_index .. code_index + duplication_count] {
+ *value = 0;
+ }
+
+ code_index += duplication_count;
+ }
+ else {
+ code_index += 1;
+ }
+ }
+
+ build_canonical_table(&mut encoding_table);
+ Ok(encoding_table)
+}
+
+// TODO Use BitStreamReader for all the bit reads?!
+#[inline]
+fn read_bits(
+ count: u64,
+ code_bits: &mut u64,
+ code_bit_count: &mut u64,
+ input: &mut impl Read,
+) -> Result<u64>
+{
+ while *code_bit_count < count {
+ read_byte(code_bits, code_bit_count, input)?;
+ }
+
+ *code_bit_count -= count;
+ Ok((*code_bits >> *code_bit_count) & ((1 << count) - 1))
+}
+
+#[inline]
+fn read_byte(code_bits: &mut u64, bit_count: &mut u64, input: &mut impl Read) -> UnitResult {
+ *code_bits = (*code_bits << 8) | u8::read(input)? as u64;
+ *bit_count += 8;
+ Ok(())
+}
+
+#[inline]
+fn read_code_into_vec(
+ code: u32,
+ run_length_code: u32,
+ code_bits: &mut u64,
+ code_bit_count: &mut u64,
+ read: &mut impl Read,
+ out: &mut Vec<u16>,
+ max_len: usize,
+) -> UnitResult
+{
+ if code == run_length_code { // code may be too large for u16
+ if *code_bit_count < 8 {
+ read_byte(code_bits, code_bit_count, read)?;
+ }
+
+ *code_bit_count -= 8;
+
+ let code_repetitions = usize::from((*code_bits >> *code_bit_count) as u8);
+
+ if out.len() + code_repetitions > max_len {
+ return Err(Error::invalid(TOO_MUCH_DATA));
+ }
+ else if out.is_empty() {
+ return Err(Error::invalid(NOT_ENOUGH_DATA));
+ }
+
+ let repeated_code = *out.last().unwrap();
+ out.extend(std::iter::repeat(repeated_code).take(code_repetitions));
+ }
+ else if out.len() < max_len { // implies that code is not larger than u16???
+ out.push(u16::try_from(code)?);
+ }
+ else {
+ return Err(Error::invalid(TOO_MUCH_DATA));
+ }
+
+ Ok(())
+}
+
+fn count_frequencies(data: &[u16]) -> Vec<u64> {
+ let mut frequencies = vec![0_u64; ENCODING_TABLE_SIZE];
+
+ for value in data {
+ frequencies[*value as usize] += 1;
+ }
+
+ frequencies
+}
+
+fn write_bits(
+ count: u64,
+ bits: u64,
+ code_bits: &mut u64,
+ code_bit_count: &mut u64,
+ mut out: impl Write,
+) -> UnitResult
+{
+ *code_bits = (*code_bits << count) | bits;
+ *code_bit_count += count;
+
+ while *code_bit_count >= 8 {
+ *code_bit_count -= 8;
+ out.write(&[
+ (*code_bits >> *code_bit_count) as u8 // TODO make sure never or always wraps?
+ ])?;
+ }
+
+ Ok(())
+}
+
+fn write_code(scode: u64, code_bits: &mut u64, code_bit_count: &mut u64, mut out: impl Write) -> UnitResult {
+ write_bits(length(scode), code(scode), code_bits, code_bit_count, &mut out)
+}
+
+#[inline(always)]
+fn send_code(
+ scode: u64,
+ run_count: u64,
+ run_code: u64,
+ code_bits: &mut u64,
+ code_bit_count: &mut u64,
+ mut out: impl Write,
+) -> UnitResult
+{
+ // Output a run of runCount instances of the symbol sCount.
+ // Output the symbols explicitly, or if that is shorter, output
+ // the sCode symbol once followed by a runCode symbol and runCount
+ // expressed as an 8-bit number.
+ if length(scode) + length(run_code) + 8 < length(scode) * run_count {
+ write_code(scode, code_bits, code_bit_count, &mut out)?;
+ write_code(run_code, code_bits, code_bit_count, &mut out)?;
+ write_bits(8, run_count, code_bits, code_bit_count, &mut out)?;
+ }
+ else {
+ for _ in 0 ..= run_count {
+ write_code(scode, code_bits, code_bit_count, &mut out)?;
+ }
+ }
+
+ Ok(())
+}
+
+fn encode_with_frequencies(
+ frequencies: &[u64],
+ uncompressed: &[u16],
+ run_length_code: usize,
+ mut out: &mut Cursor<Vec<u8>>,
+) -> Result<u64>
+{
+ let mut code_bits = 0;
+ let mut code_bit_count = 0;
+
+ let mut run_start_value = uncompressed[0];
+ let mut run_length = 0;
+
+ let start_position = out.position();
+
+ // Loop on input values
+ for &current_value in &uncompressed[1..] {
+ // Count same values or send code
+ if run_start_value == current_value && run_length < 255 {
+ run_length += 1;
+ }
+ else {
+ send_code(
+ frequencies[run_start_value as usize],
+ run_length,
+ frequencies[run_length_code],
+ &mut code_bits,
+ &mut code_bit_count,
+ &mut out,
+ )?;
+
+ run_length = 0;
+ }
+
+ run_start_value = current_value;
+ }
+
+ // Send remaining code
+ send_code(
+ frequencies[run_start_value as usize],
+ run_length,
+ frequencies[run_length_code],
+ &mut code_bits,
+ &mut code_bit_count,
+ &mut out,
+ )?;
+
+ let data_length = out.position() - start_position; // we shouldn't count the last byte write
+
+ if code_bit_count != 0 {
+ out.write(&[
+ (code_bits << (8 - code_bit_count) & 0xff) as u8
+ ])?;
+ }
+
+ Ok(data_length * 8 + code_bit_count)
+}
+
+///
+/// Pack an encoding table:
+/// - only code lengths, not actual codes, are stored
+/// - runs of zeroes are compressed as follows:
+///
+/// unpacked packed
+/// --------------------------------
+/// 1 zero 0 (6 bits)
+/// 2 zeroes 59
+/// 3 zeroes 60
+/// 4 zeroes 61
+/// 5 zeroes 62
+/// n zeroes (6 or more) 63 n-6 (6 + 8 bits)
+///
+fn pack_encoding_table(
+ frequencies: &[u64],
+ min_index: usize,
+ max_index: usize,
+ mut out: &mut Cursor<Vec<u8>>,
+) -> UnitResult
+{
+ let mut code_bits = 0_u64;
+ let mut code_bit_count = 0_u64;
+
+ let mut frequency_index = min_index;
+ while frequency_index <= max_index { // TODO slice iteration?
+ let code_length = length(frequencies[frequency_index]);
+
+ if code_length == 0 {
+ let mut zero_run = 1;
+
+ while frequency_index < max_index && zero_run < LONGEST_LONG_RUN {
+ if length(frequencies[frequency_index + 1]) > 0 {
+ break;
+ }
+
+ frequency_index += 1;
+ zero_run += 1;
+ }
+
+ if zero_run >= 2 {
+ if zero_run >= SHORTEST_LONG_RUN {
+ write_bits(6, LONG_ZEROCODE_RUN, &mut code_bits, &mut code_bit_count, &mut out)?;
+ write_bits(8, zero_run - SHORTEST_LONG_RUN, &mut code_bits, &mut code_bit_count, &mut out)?;
+ }
+ else {
+ write_bits(6, SHORT_ZEROCODE_RUN + zero_run - 2, &mut code_bits, &mut code_bit_count, &mut out)?;
+ }
+
+ frequency_index += 1; // we must increment or else this may go very wrong
+ continue;
+ }
+ }
+
+ write_bits(6, code_length, &mut code_bits, &mut code_bit_count, &mut out)?;
+ frequency_index += 1;
+ }
+
+ if code_bit_count > 0 {
+ out.write(&[
+ (code_bits << (8 - code_bit_count)) as u8
+ ])?;
+ }
+
+ Ok(())
+}
+
+/// Build a "canonical" Huffman code table:
+/// - for each (uncompressed) symbol, code contains the length
+/// of the corresponding code (in the compressed data)
+/// - canonical codes are computed and stored in code
+/// - the rules for constructing canonical codes are as follows:
+/// * shorter codes (if filled with zeroes to the right)
+/// have a numerically higher value than longer codes
+/// * for codes with the same length, numerical values
+/// increase with numerical symbol values
+/// - because the canonical code table can be constructed from
+/// symbol lengths alone, the code table can be transmitted
+/// without sending the actual code values
+/// - see http://www.compressconsult.com/huffman/
+fn build_canonical_table(code_table: &mut [u64]) {
+ debug_assert_eq!(code_table.len(), ENCODING_TABLE_SIZE);
+
+ let mut count_per_code = [0_u64; 59];
+
+ for &code in code_table.iter() {
+ count_per_code[u64_to_usize(code)] += 1;
+ }
+
+ // For each i from 58 through 1, compute the
+ // numerically lowest code with length i, and
+ // store that code in n[i].
+ {
+ let mut code = 0_u64; // TODO use foldr?
+ for count in &mut count_per_code.iter_mut().rev() {
+ let next_code = (code + *count) >> 1;
+ *count = code;
+ code = next_code;
+ }
+ }
+
+ // code[i] contains the length, l, of the
+ // code for symbol i. Assign the next available
+ // code of length l to the symbol and store both
+ // l and the code in code[i]. // TODO iter + filter ?
+ for symbol_length in code_table.iter_mut() {
+ let current_length = *symbol_length;
+ let code_index = u64_to_usize(current_length);
+ if current_length > 0 {
+ *symbol_length = current_length | (count_per_code[code_index] << 6);
+ count_per_code[code_index] += 1;
+ }
+ }
+}
+
+
+/// Compute Huffman codes (based on frq input) and store them in frq:
+/// - code structure is : [63:lsb - 6:msb] | [5-0: bit length];
+/// - max code length is 58 bits;
+/// - codes outside the range [im-iM] have a null length (unused values);
+/// - original frequencies are destroyed;
+/// - encoding tables are used by hufEncode() and hufBuildDecTable();
+///
+/// NB: The following code "(*a == *b) && (a > b))" was added to ensure
+/// elements in the heap with the same value are sorted by index.
+/// This is to ensure, the STL make_heap()/pop_heap()/push_heap() methods
+/// produced a resultant sorted heap that is identical across OSes.
+fn build_encoding_table(
+ frequencies: &mut [u64], // input frequencies, output encoding table
+) -> (usize, usize) // return frequency max min range
+{
+ debug_assert_eq!(frequencies.len(), ENCODING_TABLE_SIZE);
+
+ /// Frequency with position, used for MinHeap.
+ #[derive(Eq, PartialEq, Copy, Clone)]
+ struct HeapFrequency {
+ position: usize,
+ frequency: u64,
+ }
+
+ impl Ord for HeapFrequency {
+ fn cmp(&self, other: &Self) -> Ordering {
+ other.frequency.cmp(&self.frequency)
+ .then_with(|| other.position.cmp(&self.position))
+ }
+ }
+
+ impl PartialOrd for HeapFrequency {
+ fn partial_cmp(&self, other: &Self) -> Option<Ordering> { Some(self.cmp(other)) }
+ }
+
+ // This function assumes that when it is called, array frq
+ // indicates the frequency of all possible symbols in the data
+ // that are to be Huffman-encoded. (frq[i] contains the number
+ // of occurrences of symbol i in the data.)
+ //
+ // The loop below does three things:
+ //
+ // 1) Finds the minimum and maximum indices that point
+ // to non-zero entries in frq:
+ //
+ // frq[im] != 0, and frq[i] == 0 for all i < im
+ // frq[iM] != 0, and frq[i] == 0 for all i > iM
+ //
+ // 2) Fills array fHeap with pointers to all non-zero
+ // entries in frq.
+ //
+ // 3) Initializes array hlink such that hlink[i] == i
+ // for all array entries.
+
+ // We need to use vec here or we overflow the stack.
+ let mut links = vec![0_usize; ENCODING_TABLE_SIZE];
+ let mut frequency_heap = vec![0_usize; ENCODING_TABLE_SIZE];
+
+ // This is a good solution since we don't have usize::MAX items (no panics or UB),
+ // and since this is short-circuit, it stops at the first in order non zero element.
+ let min_frequency_index = frequencies.iter().position(|f| *f != 0).unwrap_or(0);
+
+ let mut max_frequency_index = 0;
+ let mut frequency_count = 0;
+
+ // assert bounds check to optimize away bounds check in loops
+ assert!(links.len() >= ENCODING_TABLE_SIZE);
+ assert!(frequencies.len() >= ENCODING_TABLE_SIZE);
+
+ for index in min_frequency_index..ENCODING_TABLE_SIZE {
+ links[index] = index; // TODO for x in links.iter().enumerate()
+
+ if frequencies[index] != 0 {
+ frequency_heap[frequency_count] = index;
+ max_frequency_index = index;
+ frequency_count += 1;
+ }
+ }
+
+
+ // Add a pseudo-symbol, with a frequency count of 1, to frq;
+ // adjust the fHeap and hlink array accordingly. Function
+ // hufEncode() uses the pseudo-symbol for run-length encoding.
+
+ max_frequency_index += 1;
+ frequencies[max_frequency_index] = 1;
+ frequency_heap[frequency_count] = max_frequency_index;
+ frequency_count += 1;
+
+ // Build an array, scode, such that scode[i] contains the number
+ // of bits assigned to symbol i. Conceptually this is done by
+ // constructing a tree whose leaves are the symbols with non-zero
+ // frequency:
+ //
+ // Make a heap that contains all symbols with a non-zero frequency,
+ // with the least frequent symbol on top.
+ //
+ // Repeat until only one symbol is left on the heap:
+ //
+ // Take the two least frequent symbols off the top of the heap.
+ // Create a new node that has first two nodes as children, and
+ // whose frequency is the sum of the frequencies of the first
+ // two nodes. Put the new node back into the heap.
+ //
+ // The last node left on the heap is the root of the tree. For each
+ // leaf node, the distance between the root and the leaf is the length
+ // of the code for the corresponding symbol.
+ //
+ // The loop below doesn't actually build the tree; instead we compute
+ // the distances of the leaves from the root on the fly. When a new
+ // node is added to the heap, then that node's descendants are linked
+ // into a single linear list that starts at the new node, and the code
+ // lengths of the descendants (that is, their distance from the root
+ // of the tree) are incremented by one.
+ let mut heap = BinaryHeap::with_capacity(frequency_count);
+ for index in frequency_heap.drain(..frequency_count) {
+ heap.push(HeapFrequency { position: index, frequency: frequencies[index] });
+ }
+
+ let mut s_code = vec![0_u64; ENCODING_TABLE_SIZE];
+
+ while frequency_count > 1 {
+ // Find the indices, mm and m, of the two smallest non-zero frq
+ // values in fHeap, add the smallest frq to the second-smallest
+ // frq, and remove the smallest frq value from fHeap.
+ let (high_position, low_position) = {
+ let smallest_frequency = heap.pop().expect("heap empty bug");
+ frequency_count -= 1;
+
+ let mut second_smallest_frequency = heap.peek_mut().expect("heap empty bug");
+ second_smallest_frequency.frequency += smallest_frequency.frequency;
+
+ (second_smallest_frequency.position, smallest_frequency.position)
+ };
+
+ // The entries in scode are linked into lists with the
+ // entries in hlink serving as "next" pointers and with
+ // the end of a list marked by hlink[j] == j.
+ //
+ // Traverse the lists that start at scode[m] and scode[mm].
+ // For each element visited, increment the length of the
+ // corresponding code by one bit. (If we visit scode[j]
+ // during the traversal, then the code for symbol j becomes
+ // one bit longer.)
+ //
+ // Merge the lists that start at scode[m] and scode[mm]
+ // into a single list that starts at scode[m].
+
+ // Add a bit to all codes in the first list.
+ let mut index = high_position; // TODO fold()
+ loop {
+ s_code[index] += 1;
+ debug_assert!(s_code[index] <= 58);
+
+ // merge the two lists
+ if links[index] == index {
+ links[index] = low_position;
+ break;
+ }
+
+ index = links[index];
+ }
+
+ // Add a bit to all codes in the second list
+ let mut index = low_position; // TODO fold()
+ loop {
+ s_code[index] += 1;
+ debug_assert!(s_code[index] <= 58);
+
+ if links[index] == index {
+ break;
+ }
+
+ index = links[index];
+ }
+ }
+
+ // Build a canonical Huffman code table, replacing the code
+ // lengths in scode with (code, code length) pairs. Copy the
+ // code table from scode into frq.
+ build_canonical_table(&mut s_code);
+ frequencies.copy_from_slice(&s_code);
+
+ (min_frequency_index, max_frequency_index)
+}
+
+
+#[inline] fn length(code: u64) -> u64 { code & 63 }
+#[inline] fn code(code: u64) -> u64 { code >> 6 }
+
+const INVALID_BIT_COUNT: &'static str = "invalid number of bits";
+const INVALID_TABLE_ENTRY: &'static str = "invalid code table entry";
+const NOT_ENOUGH_DATA: &'static str = "decoded data are shorter than expected";
+const INVALID_TABLE_SIZE: &'static str = "unexpected end of code table data";
+const TABLE_TOO_LONG: &'static str = "code table is longer than expected";
+const INVALID_CODE: &'static str = "invalid code";
+const TOO_MUCH_DATA: &'static str = "decoded data are longer than expected";
+
+
+#[cfg(test)]
+mod test {
+ use super::*;
+ use rand::{Rng, SeedableRng};
+
+ const UNCOMPRESSED_ARRAY: [u16; 100] = [
+ 3852, 2432, 33635, 49381, 10100, 15095, 62693, 63738, 62359, 5013, 7715, 59875, 28182,
+ 34449, 19983, 20399, 63407, 29486, 4877, 26738, 44815, 14042, 46091, 48228, 25682, 35412,
+ 7582, 65069, 6632, 54124, 13798, 27503, 52154, 61961, 30474, 46880, 39097, 15754, 52897,
+ 42371, 54053, 14178, 48276, 34591, 42602, 32126, 42062, 31474, 16274, 55991, 2882, 17039,
+ 56389, 20835, 57057, 54081, 3414, 33957, 52584, 10222, 25139, 40002, 44980, 1602, 48021,
+ 19703, 6562, 61777, 41582, 201, 31253, 51790, 15888, 40921, 3627, 12184, 16036, 26349,
+ 3159, 29002, 14535, 50632, 18118, 33583, 18878, 59470, 32835, 9347, 16991, 21303, 26263,
+ 8312, 14017, 41777, 43240, 3500, 60250, 52437, 45715, 61520,
+ ];
+
+ const UNCOMPRESSED_ARRAY_SPECIAL: [u16; 100] = [
+ 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 28182,
+ 0, 65534, 0, 65534, 0, 65534, 0, 65534, 0, 0, 0, 0, 0,
+ 0, 0, 0, 54124, 13798, 27503, 52154, 61961, 30474, 46880, 39097, 15754, 52897,
+ 42371, 54053, 14178, 48276, 34591, 42602, 32126, 42062, 31474, 16274, 55991, 2882, 17039,
+ 56389, 20835, 57057, 54081, 3414, 33957, 52584, 10222, 25139, 40002, 44980, 1602, 48021,
+ 19703, 6562, 61777, 41582, 201, 31253, 51790, 15888, 40921, 3627, 12184, 16036, 26349,
+ 3159, 29002, 14535, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+ 65534, 65534, 65534, 65534, 65534, 65534, 65534, 65534, 65534,
+ ];
+
+ const COMPRESSED_ARRAY: [u8; 703] = [
+ 0xc9, 0x0, 0x0, 0x0, 0x2e, 0xfe, 0x0, 0x0, 0x56, 0x2, 0x0, 0x0, 0xa2, 0x2, 0x0, 0x0, 0x0,
+ 0x0, 0x0, 0x0, 0x1f, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xd6, 0x47,
+ 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0x28, 0x1f, 0xff, 0xff, 0xed, 0x87, 0xff, 0xff, 0xf0,
+ 0x91, 0xff, 0xf8, 0x1f, 0xf4, 0xf1, 0xff, 0x78, 0x1f, 0xfd, 0xa1, 0xff, 0xff, 0xff, 0xff,
+ 0xff, 0xff, 0xfa, 0xc7, 0xfe, 0x4, 0x7f, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
+ 0xff, 0xed, 0x1f, 0xf3, 0xf1, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xe8, 0x7, 0xfd, 0xf8,
+ 0x7f, 0xff, 0xff, 0xff, 0xfd, 0x10, 0x7f, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0x51, 0xff,
+ 0xff, 0xff, 0xff, 0xfe, 0x1, 0xff, 0x73, 0x1f, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
+ 0xff, 0xff, 0xff, 0xff, 0xff, 0xfe, 0x0, 0x7f, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
+ 0xff, 0xff, 0xff, 0xfc, 0xa4, 0x7f, 0xf5, 0x7, 0xfc, 0x48, 0x7f, 0xe0, 0x47, 0xff, 0xff,
+ 0xf5, 0x91, 0xff, 0xff, 0xff, 0xff, 0xf1, 0xf1, 0xff, 0xff, 0xff, 0xff, 0xf8, 0x21, 0xff,
+ 0x7f, 0x1f, 0xf8, 0xd1, 0xff, 0xe7, 0x1f, 0xff, 0xff, 0xff, 0xff, 0xbc, 0x1f, 0xf2, 0x91,
+ 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0x1c, 0x1f, 0xff, 0xff, 0xff, 0xff, 0xe7,
+ 0x1f, 0xff, 0xff, 0xff, 0xff, 0xff, 0xfc, 0x8c, 0x7f, 0xff, 0xff, 0xc, 0x1f, 0xff, 0xff,
+ 0xe5, 0x7, 0xff, 0xff, 0xfa, 0x81, 0xff, 0xff, 0xff, 0x20, 0x7f, 0xff, 0xff, 0xff, 0xff,
+ 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
+ 0xff, 0xff, 0xff, 0xff, 0xff, 0xfe, 0xbc, 0x7f, 0xff, 0xff, 0xff, 0xfc, 0x38, 0x7f, 0xff,
+ 0xff, 0xff, 0xfc, 0xd0, 0x7f, 0xd3, 0xc7, 0xff, 0xff, 0xf7, 0x91, 0xff, 0xff, 0xff, 0xff,
+ 0xfe, 0xc1, 0xff, 0xff, 0xff, 0xff, 0xf9, 0x61, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xc7,
+ 0x87, 0xff, 0xff, 0xfd, 0x81, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xf1, 0x87, 0xff, 0xff,
+ 0xff, 0xff, 0xfe, 0x87, 0xff, 0x58, 0x7f, 0xff, 0xff, 0xff, 0xfd, 0xec, 0x7f, 0xff, 0xff,
+ 0xff, 0xfe, 0xd0, 0x7f, 0xff, 0xff, 0xff, 0xff, 0x6c, 0x7f, 0xcb, 0x47, 0xff, 0xff, 0xf3,
+ 0x61, 0xff, 0xff, 0xff, 0x80, 0x7f, 0xe1, 0xc7, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0x1f,
+ 0x1f, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
+ 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0x18, 0x1f, 0xff, 0xff,
+ 0xff, 0xff, 0xff, 0xfd, 0xcc, 0x7f, 0xff, 0xff, 0xff, 0xff, 0xff, 0xf8, 0x11, 0xff, 0xff,
+ 0xff, 0xff, 0xf8, 0x41, 0xff, 0xbc, 0x1f, 0xff, 0xff, 0xc4, 0x47, 0xff, 0xff, 0xf2, 0x91,
+ 0xff, 0xe0, 0x1f, 0xff, 0xff, 0xff, 0xff, 0x6d, 0x1f, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
+ 0xff, 0xff, 0xff, 0xff, 0xff, 0x2, 0x1f, 0xf9, 0xe1, 0xff, 0xff, 0xff, 0xff, 0xfc, 0xe1,
+ 0xff, 0xff, 0xfd, 0xb0, 0x7f, 0xff, 0xff, 0xff, 0xff, 0xff, 0xe1, 0xff, 0xff, 0xff, 0xff,
+ 0xff, 0xff, 0xff, 0xff, 0x5a, 0x1f, 0xfc, 0x81, 0xbf, 0x29, 0x1b, 0xff, 0xff, 0xff, 0xff,
+ 0xff, 0xff, 0xff, 0xf3, 0x61, 0xbf, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xc8, 0x1b,
+ 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xf6, 0xb1, 0xbf, 0xff, 0xfd, 0x80, 0x6f, 0xff,
+ 0xff, 0xf, 0x1b, 0xf8, 0xc1, 0xbf, 0xff, 0xfc, 0xb4, 0x6f, 0xff, 0xff, 0xff, 0xff, 0xff,
+ 0xff, 0xff, 0xda, 0x46, 0xfc, 0x54, 0x6f, 0xc9, 0x6, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
+ 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0x21, 0x1b, 0xff, 0xff, 0xe0, 0x86, 0xff, 0xff,
+ 0xff, 0xff, 0xe2, 0xc6, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
+ 0xff, 0xff, 0xff, 0xff, 0xff, 0xf3, 0x91, 0xbf, 0xff, 0xfe, 0x24, 0x6f, 0xff, 0xff, 0x6b,
+ 0x1b, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xfd, 0xb1, 0xbf, 0xfa, 0x1b, 0xfb, 0x11,
+ 0xbf, 0xff, 0xfe, 0x8, 0x6f, 0xff, 0xff, 0x42, 0x1b, 0xff, 0xff, 0xff, 0xff, 0xb9, 0x1b,
+ 0xff, 0xff, 0xcf, 0xc6, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xf1, 0x31,
+ 0x86, 0x10, 0x9, 0xb4, 0xe4, 0x4c, 0xf7, 0xef, 0x42, 0x87, 0x6a, 0xb5, 0xc2, 0x34, 0x9e,
+ 0x2f, 0x12, 0xae, 0x21, 0x68, 0xf2, 0xa8, 0x74, 0x37, 0xe1, 0x98, 0x14, 0x59, 0x57, 0x2c,
+ 0x24, 0x3b, 0x35, 0x6c, 0x1b, 0x8b, 0xcc, 0xe6, 0x13, 0x38, 0xc, 0x8e, 0xe2, 0xc, 0xfe,
+ 0x49, 0x73, 0xbc, 0x2b, 0x7b, 0x9, 0x27, 0x79, 0x14, 0xc, 0x94, 0x42, 0xf8, 0x7c, 0x1,
+ 0x8d, 0x26, 0xde, 0x87, 0x26, 0x71, 0x50, 0x45, 0xc6, 0x28, 0x40, 0xd5, 0xe, 0x8d, 0x8,
+ 0x1e, 0x4c, 0xa4, 0x79, 0x57, 0xf0, 0xc3, 0x6d, 0x5c, 0x6d, 0xc0,
+ ];
+
+ fn fill(rng: &mut impl Rng, size: usize) -> Vec<u16> {
+ if rng.gen_bool(0.2) {
+ let value = if rng.gen_bool(0.5) { 0 } else { u16::MAX };
+ return vec![ value; size ];
+ }
+
+ let mut data = vec![0_u16; size];
+
+ data.iter_mut().for_each(|v| {
+ *v = rng.gen_range(0_u16 .. u16::MAX);
+ });
+
+ data
+ }
+
+ /// Test using both input and output from a custom ILM OpenEXR test.
+ #[test]
+ fn compression_comparation() {
+ let raw = compress(&UNCOMPRESSED_ARRAY).unwrap();
+ assert_eq!(raw, COMPRESSED_ARRAY.to_vec());
+ }
+
+ #[test]
+ fn round_trip() {
+ let mut random = rand::rngs::StdRng::from_seed(SEED);
+ let raw = fill(&mut random, u16::MAX as usize);
+
+ let compressed = compress(&raw).unwrap();
+ let uncompressed = decompress(&compressed, raw.len()).unwrap();
+
+ assert_eq!(uncompressed, raw);
+ }
+
+ #[test]
+ fn repetitions_special() {
+ let raw = UNCOMPRESSED_ARRAY_SPECIAL;
+
+ let compressed = compress(&raw).unwrap();
+ let uncompressed = decompress(&compressed, raw.len()).unwrap();
+
+ assert_eq!(uncompressed, raw.to_vec());
+ }
+
+ #[test]
+ fn round_trip100() {
+ let mut random = rand::rngs::StdRng::from_seed(SEED);
+
+ for size_multiplier in 1..10 {
+ let raw = fill(&mut random, size_multiplier * 50_000);
+
+ let compressed = compress(&raw).unwrap();
+ let uncompressed = decompress(&compressed, raw.len()).unwrap();
+
+ assert_eq!(uncompressed, raw);
+ }
+ }
+
+ #[test]
+ fn test_zeroes(){
+ let uncompressed: &[u16] = &[ 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 ];
+
+ let compressed = compress(uncompressed).unwrap();
+ let decompressed = decompress(&compressed, uncompressed.len()).unwrap();
+
+ assert_eq!(uncompressed, decompressed.as_slice());
+ }
+
+ const SEED: [u8; 32] = [
+ 12,155,32,34,112,109,98,54,
+ 12,255,32,34,112,109,98,55,
+ 12,155,32,34,12,109,98,54,
+ 12,35,32,34,112,109,48,54,
+ ];
+}
Copyright © 2024 Valentin A. Popov. All Rights Reverse Engineered.