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

#[derive(Debug)]
pub struct BitWriter {
    out: Vec<u8>, // output buffer
    cache: u8,    // unwritten bits are stored here
    bits: u8,     // number of unwritten bits in cache
}

impl BitWriter {
    #[inline]
    pub fn new() -> Self {
        BitWriter {
            out: Vec::new(),
            cache: 0,
            bits: 0,
        }
    }

    #[inline]
    pub fn with_capacity(n: usize) -> Self {
        BitWriter {
            out: Vec::with_capacity(n),
            cache: 0,
            bits: 0,
        }
    }

    #[inline]
    pub fn reserve(&mut self, n: usize) {
        self.out.reserve(n / 8);
    }

    #[inline]
    fn push_unaligned(&mut self, b: u8) {
        self.out.push(self.cache | (b >> self.bits));
        self.cache = (b & ((1 << self.bits) - 1)) << (8 - self.bits);
    }

    #[inline]
    fn reset(&mut self) {
        self.cache = 0;
        self.bits = 0;
    }

    /// ```rust
    /// use treeid::bitter::*;
    ///
    /// let mut w = BitWriter::new();
    /// w.push(0xef);
    /// w.push(0x4d);
    /// assert_eq!(&[0xef, 0x4d], w.align_ref());
    /// ```
    #[inline]
    pub fn push(&mut self, b: u8) {
        // self.bits will be the same after writing 8 bits,
        // so we don't need to update that.
        if self.bits == 0 {
            self.out.push(b);
        } else {
            self.push_unaligned(b);
        }
    }

    /// ```rust
    /// use treeid::bitter::*;
    ///
    /// let mut w = BitWriter::new();
    /// w.push_bytes(&[0xef, 0x4d]);
    /// assert_eq!(&[0xef, 0x4d], w.align_ref());
    /// ```
    #[inline]
    pub fn push_bytes(&mut self, p: &[u8]) {
        // self.bits will be the same after writing 8 bits,
        // so we don't need to update that.
        if self.bits == 0 {
            self.out.extend_from_slice(p);
            return;
        }

        for &b in p {
            self.push_unaligned(b);
        }
    }

    /// ```rust
    /// use treeid::bitter::*;
    ///
    /// let mut w = BitWriter::new();
    /// w.push_bit(true);
    /// w.push_bit(true);
    /// w.push_bit(true);
    /// w.push_bit(false);
    /// w.push_bit(true);
    /// w.push_bit(true);
    /// w.push_bit(true);
    /// w.push_bit(true);
    ///
    /// w.push_bit(false);
    /// w.push_bit(true);
    /// w.push_bit(false);
    /// w.push_bit(false);
    /// w.push_bit(true);
    /// w.push_bit(true);
    /// w.push_bit(false);
    /// w.push_bit(true);
    /// assert_eq!(&[0xef, 0x4d], w.align_ref());
    /// ```
    #[inline]
    pub fn push_bit(&mut self, b: bool) {
        if self.bits == 7 {
            if b {
                self.out.push(self.cache | 1);
            } else {
                self.out.push(self.cache);
            }
            self.reset();
            return;
        }

        self.bits += 1;
        if b {
            self.cache |= 1 << (8 - self.bits);
        }
    }

    /// ```rust
    /// use treeid::bitter::*;
    ///
    /// let mut w = BitWriter::new();
    /// w.push_bits(0x08, 4);
    /// w.push_bits(0x07, 3);
    /// w.push_bits(0x05, 3);
    /// w.push_bits(0x15, 6);
    /// assert_eq!(&[0x8f, 0x55], w.align_ref());
    /// ```
    ///
    /// ```rust
    /// use treeid::bitter::*;
    ///
    /// let mut w = BitWriter::new();
    ///
    /// // 2 or 0b10
    /// let x: u64 = 2;
    /// let nz = x.leading_zeros(); // 62
    /// let nd = 63u32.saturating_sub(nz); // 1
    /// w.push_bits(std::u64::MAX, nd as u8);
    /// //assert_eq!(&[0b10000000], &w.as_ref());
    /// //w.push_bit(false);
    /// w.push_bit(false);
    /// //assert_eq!(&[0b10000000], &w.as_ref());
    /// w.push_bits(x, nd as u8);
    /// // assert_eq!(&[0b10000000], &w.as_ref());
    ///
    /// // 1 or 0b1
    /// w.push_bit(true);
    /// // assert_eq!(&[0b10010000], &w.align_ref());
    ///
    /// // 4 or 0b100
    /// let x: u64 = 4;
    /// let nz = x.leading_zeros(); // 61
    /// let nd = 63u32.saturating_sub(nz); // 2
    /// w.push_bits(std::u64::MAX, nd as u8);
    /// // assert_eq!(&[0b10011100], &w.align_ref());
    /// w.push_bit(false);
    /// // assert_eq!(&[0b10011100], &w.align_ref());
    /// w.push_bits(x, nd as u8);
    /// println!("{:?}", w);
    /// assert_eq!(&[0b10011100, 0b00000000], &w.align_ref());
    /// println!("{:?}", w);
    /// ```
    #[inline]
    pub fn push_bits(&mut self, r: u64, n: u8) {
        if n == 0 {
            return;
        }
        let mut n = n;

        // the bits higher than n are read as well,
        // so they must be zeroed.
        let r = (r << 64 - n) >> 64 - n;

        let new_bits = self.bits + n;
        if new_bits < 8 {
            // r fits into cache, no write will occur to out
            self.cache |= (r as u8) << (8 - new_bits);
            self.bits = new_bits;
            return;
        }

        if new_bits > 8 {
            // cache will be filled, and there will be more bits to write

            // fill cache and write it out
            let free = 8 - self.bits;
            self.out.push(self.cache | ((r >> (n - free)) as u8));
            n -= free;

            // write out whole bytes
            while n >= 8 {
                n -= 8;
                // no need to mask r, converting to u8 will mask
                // out higher bits
                self.out.push((r >> n) as u8);
            }

            // put remaining into cache
            if n > 0 {
                // note: n < 8 (in case of n=8, 1<<n would overflow u8)
                self.cache = ((r as u8) & ((1 << n) - 1)) << (8 - n);
                self.bits = n;
            } else {
                self.reset();
            }
            return;
        }

        // cache will be filled exactly with the bits to be written
        self.out.push(self.cache | r as u8);
        self.reset();
    }

    /// ```rust
    /// use treeid::bitter::*;
    ///
    /// let mut w = BitWriter::new();
    /// w.push(0xc1);
    /// w.push_bit(false);
    /// w.push_bits(0x3f, 6);
    /// w.push_bit(true);
    /// w.push(0xac);
    /// w.push_bits(0x01, 1);
    /// w.push_bits(0x1248f, 20);
    /// assert_eq!(3, w.align());
    /// w.push_bytes(&[0x01, 0x02]);
    /// w.push_bits(0x0f, 4);
    /// w.push_bytes(&[0x80, 0x8f]);
    /// assert_eq!(4, w.align());
    /// assert_eq!(0, w.align());
    /// w.push_bits(0x01, 1);
    /// w.push(0xff);
    /// assert_eq!(
    ///     &[0xc1, 0x7f, 0xac, 0x89, 0x24, 0x78, 0x01, 0x02, 0xf8, 0x08, 0xf0, 0xff, 0x80],
    ///     w.align_ref(),
    /// );
    /// ```
    #[inline]
    pub fn align(&mut self) -> u8 {
        let mut skipped: u8 = 0;
        if self.bits > 0 {
            self.out.push(self.cache);
            skipped = 8 - self.bits;
            self.reset();
        }
        skipped
    }

    /// Not safe to call unless aligned (!)
    ///
    /// ```rust
    /// use treeid::bitter::*;
    ///
    /// let mut w = BitWriter::new();
    /// w.push(1);
    /// assert_eq!(&[1], w.align_ref());
    /// w.trailing_pad(4);
    /// assert_eq!(&[1, 0, 0, 0], w.align_ref());
    /// ```
    #[inline]
    pub fn trailing_pad(&mut self, boundary: usize) -> usize {
        let pad_bytes = self.out.len() % boundary;
        if pad_bytes > 0 {
            for _ in 0..boundary - pad_bytes {
                self.out.push(0x0);
            }
        }
        pad_bytes
    }

    #[inline]
    pub fn to_vec(self) -> Vec<u8> {
        self.out
    }

    #[inline]
    pub fn align_vec(mut self) -> Vec<u8> {
        self.align();
        self.out
    }

    #[inline]
    pub fn align_ref(&mut self) -> &[u8] {
        self.align();
        &self.out
    }
}

impl AsRef<[u8]> for BitWriter {
    #[inline]
    fn as_ref(&self) -> &[u8] {
        &self.out
    }
}