1
  2
  3
  4
  5
  6
  7
  8
  9
 10
 11
 12
 13
 14
 15
 16
 17
 18
 19
 20
 21
 22
 23
 24
 25
 26
 27
 28
 29
 30
 31
 32
 33
 34
 35
 36
 37
 38
 39
 40
 41
 42
 43
 44
 45
 46
 47
 48
 49
 50
 51
 52
 53
 54
 55
 56
 57
 58
 59
 60
 61
 62
 63
 64
 65
 66
 67
 68
 69
 70
 71
 72
 73
 74
 75
 76
 77
 78
 79
 80
 81
 82
 83
 84
 85
 86
 87
 88
 89
 90
 91
 92
 93
 94
 95
 96
 97
 98
 99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
// Copyright 2017 Brian Langenberger
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.

//! Traits and implementations for reading or writing Huffman codes
//! from or to a stream.

#![warn(missing_docs)]

use super::BitQueue;
use super::Endianness;
use std::collections::BTreeMap;
use std::fmt;
use std::marker::PhantomData;

/// A compiled Huffman tree element for use with the `read_huffman` method.
/// Returned by `compile_read_tree`.
///
/// Compiled read trees are optimized for faster lookup
/// and are therefore endian-specific.
///
/// In addition, each symbol in the source tree may occur many times
/// in the compiled tree.  If symbols require a nontrivial amount of space,
/// consider using reference counting so that they may be cloned
/// more efficiently.
pub enum ReadHuffmanTree<E: Endianness, T: Clone> {
    /// The final value and new reader state
    Done(T, u8, u32, PhantomData<E>),
    /// Another byte is necessary to determine final value
    Continue(Box<[ReadHuffmanTree<E, T>]>),
    /// An invalid reader state has been used
    InvalidState,
}

/// Given a vector of symbol/code pairs, compiles a Huffman tree
/// for reading.
///
/// Code must be 0 or 1 bits and are always read from the stream
/// from least-significant in the list to most signficant
/// (which makes them easier to read for humans).
///
/// All possible codes must be assigned some symbol,
/// and it is acceptable for the same symbol to occur multiple times.
///
/// ## Examples
/// ```
/// use bitstream_io::huffman::compile_read_tree;
/// use bitstream_io::BigEndian;
/// assert!(compile_read_tree::<BigEndian,i32>(
///     vec![(1, vec![0]),
///          (2, vec![1, 0]),
///          (3, vec![1, 1])]).is_ok());
/// ```
///
/// ```
/// use std::io::{Read, Cursor};
/// use bitstream_io::{BigEndian, BitReader};
/// use bitstream_io::huffman::compile_read_tree;
/// let tree = compile_read_tree(
///     vec![('a', vec![0]),
///          ('b', vec![1, 0]),
///          ('c', vec![1, 1, 0]),
///          ('d', vec![1, 1, 1])]).unwrap();
/// let data = [0b10110111];
/// let mut cursor = Cursor::new(&data);
/// let mut reader = BitReader::endian(&mut cursor, BigEndian);
/// assert_eq!(reader.read_huffman(&tree).unwrap(), 'b');
/// assert_eq!(reader.read_huffman(&tree).unwrap(), 'c');
/// assert_eq!(reader.read_huffman(&tree).unwrap(), 'd');
/// ```
pub fn compile_read_tree<E, T>(
    values: Vec<(T, Vec<u8>)>,
) -> Result<Box<[ReadHuffmanTree<E, T>]>, HuffmanTreeError>
where
    E: Endianness,
    T: Clone,
{
    let tree = FinalHuffmanTree::new(values)?;

    let mut result = Vec::with_capacity(256);
    result.extend((0..256).map(|_| ReadHuffmanTree::InvalidState));
    let queue = BitQueue::from_value(0, 0);
    let i = queue.to_state();
    result[i] = compile_queue(queue, &tree);
    for bits in 1..8 {
        for value in 0..(1 << bits) {
            let queue = BitQueue::from_value(value, bits);
            let i = queue.to_state();
            result[i] = compile_queue(queue, &tree);
        }
    }
    assert_eq!(result.len(), 256);
    Ok(result.into_boxed_slice())
}

fn compile_queue<E, T>(
    mut queue: BitQueue<E, u8>,
    tree: &FinalHuffmanTree<T>,
) -> ReadHuffmanTree<E, T>
where
    E: Endianness,
    T: Clone,
{
    match tree {
        FinalHuffmanTree::Leaf(ref value) => {
            let len = queue.len();
            ReadHuffmanTree::Done(value.clone(), queue.value(), len, PhantomData)
        }
        FinalHuffmanTree::Tree(ref bit0, ref bit1) => {
            if queue.is_empty() {
                ReadHuffmanTree::Continue(
                    (0..256)
                        .map(|byte| compile_queue(BitQueue::from_value(byte as u8, 8), &tree))
                        .collect::<Vec<ReadHuffmanTree<E, T>>>()
                        .into_boxed_slice(),
                )
            } else if queue.pop(1) == 0 {
                compile_queue(queue, bit0)
            } else {
                compile_queue(queue, bit1)
            }
        }
    }
}

// A complete Huffman tree with no empty nodes
enum FinalHuffmanTree<T: Clone> {
    Leaf(T),
    Tree(Box<FinalHuffmanTree<T>>, Box<FinalHuffmanTree<T>>),
}

impl<T: Clone> FinalHuffmanTree<T> {
    fn new(values: Vec<(T, Vec<u8>)>) -> Result<FinalHuffmanTree<T>, HuffmanTreeError> {
        let mut tree = WipHuffmanTree::new_empty();

        for (symbol, code) in values {
            tree.add(code.as_slice(), symbol)?;
        }

        tree.into_read_tree()
    }
}

// Work-in-progress trees may have empty nodes during construction
// but those are not allowed in a finalized tree.
// If the user wants some codes to be None or an error symbol of some sort,
// those will need to be specified explicitly.
enum WipHuffmanTree<T: Clone> {
    Empty,
    Leaf(T),
    Tree(Box<WipHuffmanTree<T>>, Box<WipHuffmanTree<T>>),
}

impl<T: Clone> WipHuffmanTree<T> {
    fn new_empty() -> WipHuffmanTree<T> {
        WipHuffmanTree::Empty
    }

    fn new_leaf(value: T) -> WipHuffmanTree<T> {
        WipHuffmanTree::Leaf(value)
    }

    fn new_tree() -> WipHuffmanTree<T> {
        WipHuffmanTree::Tree(Box::new(Self::new_empty()), Box::new(Self::new_empty()))
    }

    fn into_read_tree(self) -> Result<FinalHuffmanTree<T>, HuffmanTreeError> {
        match self {
            WipHuffmanTree::Empty => Err(HuffmanTreeError::MissingLeaf),
            WipHuffmanTree::Leaf(v) => Ok(FinalHuffmanTree::Leaf(v)),
            WipHuffmanTree::Tree(zero, one) => {
                let zero = zero.into_read_tree()?;
                let one = one.into_read_tree()?;
                Ok(FinalHuffmanTree::Tree(Box::new(zero), Box::new(one)))
            }
        }
    }

    fn add(&mut self, code: &[u8], symbol: T) -> Result<(), HuffmanTreeError> {
        match self {
            WipHuffmanTree::Empty => {
                if code.is_empty() {
                    *self = WipHuffmanTree::new_leaf(symbol);
                    Ok(())
                } else {
                    *self = WipHuffmanTree::new_tree();
                    self.add(code, symbol)
                }
            }
            WipHuffmanTree::Leaf(_) => Err(if code.is_empty() {
                HuffmanTreeError::DuplicateLeaf
            } else {
                HuffmanTreeError::OrphanedLeaf
            }),
            WipHuffmanTree::Tree(ref mut zero, ref mut one) => {
                if code.is_empty() {
                    Err(HuffmanTreeError::DuplicateLeaf)
                } else {
                    match code[0] {
                        0 => zero.add(&code[1..], symbol),
                        1 => one.add(&code[1..], symbol),
                        _ => Err(HuffmanTreeError::InvalidBit),
                    }
                }
            }
        }
    }
}

/// An error type during Huffman tree compilation.
#[derive(PartialEq, Copy, Clone, Debug)]
pub enum HuffmanTreeError {
    /// One of the bits in a Huffman code is not 0 or 1
    InvalidBit,
    /// A Huffman code in the specification has no defined symbol
    MissingLeaf,
    /// The same Huffman code specifies multiple symbols
    DuplicateLeaf,
    /// A Huffman code is the prefix of some longer code
    OrphanedLeaf,
}

impl fmt::Display for HuffmanTreeError {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        match *self {
            HuffmanTreeError::InvalidBit => write!(f, "invalid bit in code"),
            HuffmanTreeError::MissingLeaf => write!(f, "missing leaf node in specification"),
            HuffmanTreeError::DuplicateLeaf => write!(f, "duplicate leaf node in specification"),
            HuffmanTreeError::OrphanedLeaf => write!(f, "orphaned leaf node in specification"),
        }
    }
}

/// Given a vector of symbol/code pairs, compiles a Huffman tree
/// for writing.
///
/// Code must be 0 or 1 bits and are always written to the stream
/// from least-significant in the list to most signficant
/// (which makes them easier to read for humans).
///
/// If the same symbol occurs multiple times, the first code is used.
/// Unlike in read trees, not all possible codes need to be
/// assigned a symbol.
///
/// ## Examples
/// ```
/// use bitstream_io::huffman::compile_write_tree;
/// use bitstream_io::BigEndian;
/// assert!(compile_write_tree::<BigEndian,i32>(
///     vec![(1, vec![0]),
///          (2, vec![1, 0]),
///          (3, vec![1, 1])]).is_ok());
/// ```
///
/// ```
/// use std::io::Write;
/// use bitstream_io::{BigEndian, BitWriter};
/// use bitstream_io::huffman::compile_write_tree;
/// let tree = compile_write_tree(
///     vec![('a', vec![0]),
///          ('b', vec![1, 0]),
///          ('c', vec![1, 1, 0]),
///          ('d', vec![1, 1, 1])]).unwrap();
/// let mut data = Vec::new();
/// {
///     let mut writer = BitWriter::endian(&mut data, BigEndian);
///     writer.write_huffman(&tree, 'b').unwrap();
///     writer.write_huffman(&tree, 'c').unwrap();
///     writer.write_huffman(&tree, 'd').unwrap();
/// }
/// assert_eq!(data, [0b10110111]);
/// ```
pub fn compile_write_tree<E, T>(
    values: Vec<(T, Vec<u8>)>,
) -> Result<WriteHuffmanTree<E, T>, HuffmanTreeError>
where
    E: Endianness,
    T: Ord + Clone,
{
    let mut map = BTreeMap::new();

    for (symbol, code) in values {
        let mut encoded = Vec::new();
        for bits in code.chunks(32) {
            let mut acc = BitQueue::<E, u32>::new();
            for bit in bits {
                match *bit {
                    0 => acc.push(1, 0),
                    1 => acc.push(1, 1),
                    _ => return Err(HuffmanTreeError::InvalidBit),
                }
            }
            let len = acc.len();
            encoded.push((len, acc.value()))
        }
        map.entry(symbol)
            .or_insert_with(|| encoded.into_boxed_slice());
    }

    Ok(WriteHuffmanTree {
        map,
        phantom: PhantomData,
    })
}

/// A compiled Huffman tree for use with the `write_huffman` method.
/// Returned by `compiled_write_tree`.
pub struct WriteHuffmanTree<E: Endianness, T: Ord> {
    map: BTreeMap<T, Box<[(u32, u32)]>>,
    phantom: PhantomData<E>,
}

impl<E: Endianness, T: Ord + Clone> WriteHuffmanTree<E, T> {
    /// Returns true if symbol is in tree.
    #[inline]
    pub fn has_symbol(&self, symbol: &T) -> bool {
        self.map.contains_key(symbol)
    }

    /// Given symbol, returns (bits, value) pairs for writing code.
    /// Panics if symbol is not found.
    #[inline]
    pub fn get(&self, symbol: &T) -> &[(u32, u32)] {
        self.map[symbol].as_ref()
    }
}