nihav-core/src/io/codebook.rs

   1 //! Codebook support for bitstream reader.
   2 //!
   3 //! Codebook is a set of unique bit strings and values assigned to them.
   4 //! Since there are many ways to define codebook, this implementation employs [`CodebookDescReader`] trait to provide codebook generator with the codes.
   5 //! Please also pay attention to the codebook creation mode: if bitstream reader reads bits starting from most significant bit first then you should use [`MSB`] mode and [`LSB`] mode otherwise.
   6 //!
   7 //! # Examples
   8 //!
   9 //! Create a codebook from arrays with codeword descriptions:
  10 //! ```
  11 //! use nihav_core::io::codebook::{ShortCodebookDesc, ShortCodebookDescReader, Codebook, CodebookMode};
  12 //!
  13 //! let cb_desc: Vec<ShortCodebookDesc> = vec!(
  14 //!             ShortCodebookDesc { code: 0b00,   bits: 2 },
  15 //!             ShortCodebookDesc { code: 0,      bits: 0 },
  16 //!             ShortCodebookDesc { code: 0b01,   bits: 2 },
  17 //!             ShortCodebookDesc { code: 0b1,    bits: 1 });
  18 //! let mut cr = ShortCodebookDescReader::new(cb_desc);
  19 //! let cb = Codebook::new(&mut cr, CodebookMode::LSB).unwrap();
  20 //! ```
  21 //!
  22 //! Create a codebook using more flexible [`TableCodebookDescReader`] approach.
  23 //! This will create a codebook for the following set: `1` -> -2, `01` -> -1, `001` -> 0, `0001` -> 1, `00001` -> 2.
  24 //! ```
  25 //! use nihav_core::io::codebook::{TableCodebookDescReader, Codebook, CodebookMode};
  26 //!
  27 //! fn map_cb_index(index: usize) -> i16 { (index as i16) - 2 }
  28 //! const CB_BITS:  [u8; 5] = [ 1, 2, 3, 4, 5 ];
  29 //! const CB_CODES: [u8; 5] = [ 1, 1, 1, 1, 1 ];
  30 //!
  31 //! let mut tcr = TableCodebookDescReader::new(&CB_CODES, &CB_BITS, map_cb_index);
  32 //! let cb = Codebook::new(&mut tcr, CodebookMode::MSB).unwrap();
  33 //! ```
  34 //!
  35 //! Read value using a codebook:
  36 //! ```no_run
  37 //! use nihav_core::io::bitreader::BitReader;
  38 //! use nihav_core::io::codebook::{Codebook, CodebookReader, CodebookMode};
  39 //! # use nihav_core::io::codebook::{ShortCodebookDesc, ShortCodebookDescReader, CodebookDescReader, CodebookResult};
  40 //!
  41 //! # fn foo(br: &mut BitReader) -> CodebookResult<()> {
  42 //! # let mut cr = ShortCodebookDescReader::new(vec![ShortCodebookDesc { code: 0b00,   bits: 2 }]);
  43 //! let cb = Codebook::new(&mut cr, CodebookMode::MSB).unwrap();
  44 //! let value = br.read_cb(&cb)?;
  45 //! # Ok(())
  46 //! # }
  47 //! ```
  48 //!
  49 //! [`MSB`]: ./enum.CodebookMode.html#variant.MSB
  50 //! [`LSB`]: ./enum.CodebookMode.html#variant.LSB
  51 //! [`CodebookDescReader`]: ./trait.CodebookDescReader.html
  52 //! [`TableCodebookDescReader`]: ./struct.TableCodebookDescReader.html
  53
  54 use std::collections::HashMap;
  55 use std::cmp::{max, min};
  56 use super::bitreader::BitReader;
  57
  58 /// A list specifying general codebook operations errors.
  59 #[derive(Debug)]
  60 pub enum CodebookError {
  61     /// Codebook description contains errors.
  62     InvalidCodebook,
  63     /// Could not allocate memory for codebook.
  64     MemoryError,
  65     /// Bitstream contains a sequence not present in codebook.
  66     InvalidCode,
  67 }
  68
  69 /// Codebook operation modes.
  70 #[derive(Debug, Copy, Clone)]
  71 pub enum CodebookMode {
  72     /// Codes in the codebook should be read most significant bit first.
  73     MSB,
  74     /// Codes in the codebook should be read least significant bit first.
  75     LSB,
  76 }
  77
  78 /// A specialised `Result` type for codebook operations.
  79 pub type CodebookResult<T> = Result<T, CodebookError>;
  80
  81 /// Codebook description for `(code bits, code length, code value)` triplet.
  82 ///
  83 /// This should be used to create a list of codeword definitions for [`FullCodebookDescReader`].
  84 ///
  85 /// [`FullCodebookDescReader`]: ./struct.FullCodebookDescReader.html
  86 #[derive(Clone,Copy)]
  87 pub struct FullCodebookDesc<S> {
  88     /// Codeword bits.
  89     pub code: u32,
  90     /// Codeword length.
  91     pub bits: u8,
  92     /// Codeword value (symbol).
  93     pub sym:  S,
  94 }
  95
  96 /// Codebook description for `(code bits, code length)` pair with array index being used as codeword value.
  97 ///
  98 /// This should be used to create a list of codeword definitions for [`ShortCodebookDescReader`].
  99 ///
 100 /// [`ShortCodebookDescReader`]: ./struct.ShortCodebookDescReader.html
 101 #[derive(Clone,Copy)]
 102 pub struct ShortCodebookDesc {
 103     /// Codeword bits.
 104     pub code: u32,
 105     /// Codeword length.
 106     pub bits: u8,
 107 }
 108
 109 /// The interface for providing a list of codeword definitions to the codebook creator.
 110 ///
 111 /// The structure implementing this trait should be able to provide the total number of defined codewords and their bits and values. [`ShortCodebookDescReader`] or [`TableCodebookDescReader`] are some examples of such implementation.
 112 /// Codeword definitions with zero length are ignored (those may be used to create sparse codebook definitions though).
 113 ///
 114 /// [`ShortCodebookDescReader`]: ./struct.ShortCodebookDescReader.html
 115 /// [`TableCodebookDescReader`]: ./struct.TableCodebookDescReader.html
 116 pub trait CodebookDescReader<S> {
 117     /// Returns the codeword length for the provided index.
 118     fn bits(&mut self, idx: usize) -> u8;
 119     /// Returns the codeword bits for the provided index.
 120     fn code(&mut self, idx: usize) -> u32;
 121     /// Returns the codeword value (aka codeword symbol) for the provided index.
 122     fn sym (&mut self, idx: usize) -> S;
 123     /// Returns the total number of defined codewords.
 124     fn len (&mut self)             -> usize;
 125 }
 126
 127 /// The codebook structure for code reading.
 128 #[allow(dead_code)]
 129 pub struct Codebook<S> {
 130     table: Vec<u32>,
 131     syms:  Vec<S>,
 132     lut_bits: u8,
 133 }
 134
 135 /// Trait allowing bitreader to use codebook for decoding bit sequences.
 136 pub trait CodebookReader<S> {
 137     /// Reads the codeword from the bitstream and returns its value (or [`InvalidCode`] on error).
 138     ///
 139     /// [`InvalidCode`]: ./enum.CodebookError.html#variant.InvalidCode
 140     fn read_cb(&mut self, cb: &Codebook<S>) -> CodebookResult<S>;
 141 }
 142
 143 const TABLE_FILL_VALUE: u32 = 0x7F;
 144 const MAX_LUT_BITS: u8 = 10;
 145
 146 fn fill_lut_msb(table: &mut Vec<u32>, off: usize,
 147                 code: u32, bits: u8, lut_bits: u8, symidx: u32, esc: bool) {
 148     if !esc {
 149         let fill_len  = lut_bits - bits;
 150         let fill_size = 1 << fill_len;
 151         let fill_code = code << (lut_bits - bits);
 152         let lut_value = (symidx << 8) | u32::from(bits);
 153         for j in 0..fill_size {
 154             let idx = (fill_code + j) as usize;
 155             table[idx + off] = lut_value;
 156         }
 157     } else {
 158         let idx = (code as usize) + off;
 159         table[idx] = (symidx << 8) | 0x80 | u32::from(bits);
 160     }
 161 }
 162
 163 fn fill_lut_lsb(table: &mut Vec<u32>, off: usize,
 164                 code: u32, bits: u8, lut_bits: u8, symidx: u32, esc: bool) {
 165     if !esc {
 166         let fill_len  = lut_bits - bits;
 167         let fill_size = 1 << fill_len;
 168         let fill_code = code;
 169         let step = lut_bits - fill_len;
 170         for j in 0..fill_size {
 171             let idx = (fill_code + (j << step)) as usize;
 172             table[idx + off] = (symidx << 8) | u32::from(bits);
 173         }
 174     } else {
 175         let idx = (code as usize) + off;
 176         table[idx] = (symidx << 8) | 0x80 | u32::from(bits);
 177     }
 178 }
 179
 180 fn fill_lut(table: &mut Vec<u32>, mode: CodebookMode,
 181             off: usize, code: u32, bits: u8, lut_bits: u8, symidx: u32, esc: bool) -> bool {
 182     match mode {
 183         CodebookMode::MSB => fill_lut_msb(table, off, code, bits, lut_bits, symidx, esc),
 184         CodebookMode::LSB => fill_lut_lsb(table, off, code, bits, lut_bits, symidx, esc),
 185     };
 186     bits > lut_bits
 187 }
 188
 189 fn resize_table(table: &mut Vec<u32>, bits: u8) -> CodebookResult<u32> {
 190     let add_size = (1 << bits) as usize;
 191     table.reserve(add_size);
 192     let cur_off = table.len() as u32;
 193     let new_size = table.len() + add_size;
 194     if table.capacity() < new_size { return Err(CodebookError::MemoryError); }
 195     table.resize(new_size, TABLE_FILL_VALUE);
 196     Ok(cur_off)
 197 }
 198
 199
 200 fn extract_lut_part(code: u32, bits: u8, lut_bits: u8, mode: CodebookMode) -> u32 {
 201     match mode {
 202         CodebookMode::MSB => code >> (bits - lut_bits),
 203         CodebookMode::LSB => code & ((1 << lut_bits) - 1),
 204     }
 205 }
 206
 207 fn extract_esc_part(code: u32, bits: u8, lut_bits: u8, mode: CodebookMode) -> u32 {
 208     match mode {
 209         CodebookMode::MSB => code & ((1 << (bits - lut_bits)) - 1),
 210         CodebookMode::LSB => code >> lut_bits,
 211     }
 212 }
 213
 214 #[derive(Clone,Copy)]
 215 struct Code {
 216     code: u32,
 217     bits: u8,
 218     idx:  usize,
 219 }
 220
 221 struct CodeBucket {
 222     maxlen: u8,
 223     offset: usize,
 224     codes:  Vec<Code>,
 225 }
 226
 227 impl CodeBucket {
 228     fn new() -> Self {
 229         CodeBucket { maxlen: 0, offset: 0, codes: Vec::new() }
 230     }
 231     fn add_code(&mut self, c: Code) {
 232         if c.bits > self.maxlen { self.maxlen = c.bits; }
 233         self.codes.push(c);
 234     }
 235 }
 236
 237 type EscapeCodes = HashMap<u32, CodeBucket>;
 238
 239 fn add_esc_code(cc: &mut EscapeCodes, key: u32, code: u32, bits: u8, idx: usize) {
 240     cc.entry(key).or_insert_with(CodeBucket::new);
 241     let b = cc.get_mut(&key);
 242     if let Some(bucket) = b {
 243         bucket.add_code(Code {code, bits, idx });
 244     } else { panic!("no bucket when expected!"); }
 245 }
 246
 247 fn build_esc_lut(table: &mut Vec<u32>,
 248                  mode: CodebookMode,
 249                  bucket: &CodeBucket) -> CodebookResult<()> {
 250     let mut escape_list: EscapeCodes = HashMap::new();
 251     let maxlen = if bucket.maxlen > MAX_LUT_BITS { MAX_LUT_BITS } else { bucket.maxlen };
 252
 253     for code in &bucket.codes {
 254         let bits = code.bits;
 255         if code.bits <= MAX_LUT_BITS {
 256             fill_lut(table, mode, bucket.offset, code.code, bits,
 257                      maxlen, code.idx as u32, false);
 258         } else {
 259             let ckey = extract_lut_part(code.code, bits, MAX_LUT_BITS, mode);
 260             let cval = extract_esc_part(code.code, bits, MAX_LUT_BITS, mode);
 261             add_esc_code(&mut escape_list, ckey, cval, bits - MAX_LUT_BITS, code.idx);
 262         }
 263     }
 264
 265     let cur_offset = bucket.offset;
 266     for (ckey, sec_bucket) in &mut escape_list {
 267         let key = *ckey as u32;
 268         let maxlen = min(sec_bucket.maxlen, MAX_LUT_BITS);
 269         let new_off = resize_table(table, maxlen)?;
 270         fill_lut(table, mode, cur_offset, key, maxlen,
 271                  MAX_LUT_BITS, new_off, true);
 272         sec_bucket.offset = new_off as usize;
 273     }
 274
 275     for sec_bucket in escape_list.values() {
 276         build_esc_lut(table, mode, sec_bucket)?;
 277     }
 278
 279     Ok(())
 280 }
 281
 282 impl<S: Copy> Codebook<S> {
 283
 284     /// Constructs a new `Codebook` instance using provided codebook description and mode.
 285     pub fn new(cb: &mut CodebookDescReader<S>, mode: CodebookMode) -> CodebookResult<Self> {
 286         let mut maxbits = 0;
 287         let mut nnz = 0;
 288         let mut escape_list: EscapeCodes = HashMap::new();
 289
 290         let mut symidx: usize = 0;
 291         for i in 0..cb.len() {
 292             let bits = cb.bits(i);
 293             if bits > 0 {
 294                 nnz += 1;
 295                 if cb.code(i) >= (1 << bits) {
 296                     return Err(CodebookError::InvalidCodebook);
 297                 }
 298             }
 299             maxbits = max(bits, maxbits);
 300             if bits > MAX_LUT_BITS {
 301                 let code = cb.code(i);
 302                 let ckey = extract_lut_part(code, bits, MAX_LUT_BITS, mode);
 303                 let cval = extract_esc_part(code, bits, MAX_LUT_BITS, mode);
 304                 add_esc_code(&mut escape_list, ckey, cval, bits - MAX_LUT_BITS, symidx);
 305             }
 306             if bits > 0 { symidx += 1; }
 307         }
 308         if maxbits == 0 { return Err(CodebookError::InvalidCodebook); }
 309
 310         if maxbits > MAX_LUT_BITS { maxbits = MAX_LUT_BITS; }
 311
 312         let tab_len = 1 << maxbits;
 313         let mut table: Vec<u32> = Vec::with_capacity(tab_len);
 314         let mut syms:  Vec<S>   = Vec::with_capacity(nnz);
 315         if table.capacity() < tab_len { return Err(CodebookError::MemoryError); }
 316         if syms.capacity()  < nnz     { return Err(CodebookError::MemoryError); }
 317         table.resize(tab_len, TABLE_FILL_VALUE);
 318
 319         let mut symidx: u32 = 0;
 320         for i in 0..cb.len() {
 321             let bits = cb.bits(i);
 322             let code = cb.code(i);
 323             if bits == 0 { continue; }
 324             if bits <= MAX_LUT_BITS {
 325                 fill_lut(&mut table, mode, 0, code, bits, maxbits, symidx, false);
 326             } else {
 327                 let ckey = extract_lut_part(code, bits, MAX_LUT_BITS, mode) as usize;
 328                 if table[ckey] == TABLE_FILL_VALUE {
 329                     let key = ckey as u32;
 330                     if let Some(bucket) = escape_list.get_mut(&key) {
 331                         let maxlen = min(bucket.maxlen, MAX_LUT_BITS);
 332                         let new_off = resize_table(&mut table, maxlen)?;
 333                         fill_lut(&mut table, mode, 0, key, maxlen, MAX_LUT_BITS, new_off, true);
 334                         bucket.offset = new_off as usize;
 335                     }
 336                 }
 337             }
 338             symidx += 1;
 339         }
 340
 341         for bucket in escape_list.values() {
 342             build_esc_lut(&mut table, mode, &bucket)?;
 343         }
 344
 345         for i in 0..cb.len() {
 346             if cb.bits(i) > 0 {
 347                 syms.push(cb.sym(i));
 348             }
 349         }
 350
 351         Ok(Codebook { table, syms, lut_bits: maxbits })
 352     }
 353 }
 354
 355 impl<'a, S: Copy> CodebookReader<S> for BitReader<'a> {
 356     #[allow(unused_variables)]
 357     fn read_cb(&mut self, cb: &Codebook<S>) -> CodebookResult<S> {
 358         let mut esc = true;
 359         let mut idx = 0;
 360         let mut lut_bits = cb.lut_bits;
 361         while esc {
 362             let lut_idx = (self.peek(lut_bits) as usize) + (idx as usize);
 363             if cb.table[lut_idx] == TABLE_FILL_VALUE { return Err(CodebookError::InvalidCode); }
 364             let bits = cb.table[lut_idx] & 0x7F;
 365             esc  = (cb.table[lut_idx] & 0x80) != 0;
 366             idx  = (cb.table[lut_idx] >> 8) as usize;
 367             if (bits as isize) > self.left() {
 368                 return Err(CodebookError::InvalidCode);
 369             }
 370             let skip_bits = if esc { u32::from(lut_bits) } else { bits };
 371             self.skip(skip_bits as u32).unwrap();
 372             lut_bits = bits as u8;
 373         }
 374         Ok(cb.syms[idx])
 375     }
 376 }
 377
 378 /// Codebook description that stores a list of codewords and their values.
 379 pub struct FullCodebookDescReader<S> {
 380     data: Vec<FullCodebookDesc<S>>,
 381 }
 382
 383 impl<S> FullCodebookDescReader<S> {
 384     /// Constructs a new `FullCodebookDescReader` instance.
 385     pub fn new(data: Vec<FullCodebookDesc<S>>) -> Self {
 386         FullCodebookDescReader { data }
 387     }
 388 }
 389
 390 impl<S: Copy> CodebookDescReader<S> for FullCodebookDescReader<S> {
 391     fn bits(&mut self, idx: usize) -> u8  { self.data[idx].bits }
 392     fn code(&mut self, idx: usize) -> u32 { self.data[idx].code }
 393     fn sym (&mut self, idx: usize) -> S   { self.data[idx].sym  }
 394     fn len(&mut self) -> usize { self.data.len() }
 395 }
 396
 397 /// Codebook description that stores a list of codewords and their value is equal to the index.
 398 pub struct ShortCodebookDescReader {
 399     data: Vec<ShortCodebookDesc>,
 400 }
 401
 402 impl ShortCodebookDescReader {
 403     /// Constructs a new `ShortCodebookDescReader` instance.
 404     pub fn new(data: Vec<ShortCodebookDesc<>>) -> Self {
 405         ShortCodebookDescReader { data }
 406     }
 407 }
 408
 409 impl CodebookDescReader<u32> for ShortCodebookDescReader {
 410     fn bits(&mut self, idx: usize) -> u8  { self.data[idx].bits }
 411     fn code(&mut self, idx: usize) -> u32 { self.data[idx].code }
 412     fn sym (&mut self, idx: usize) -> u32 { idx as u32 }
 413     fn len(&mut self) -> usize { self.data.len() }
 414 }
 415
 416 /// Flexible codebook description that uses two separate arrays for codeword bits and lengths and a function that maps codeword index into its symbol.
 417 pub struct TableCodebookDescReader<'a, CodeType:'static, IndexType:'static> {
 418     bits:       &'a [u8],
 419     codes:      &'a [CodeType],
 420     idx_map:    fn(usize) -> IndexType,
 421 }
 422
 423 impl<'a, CodeType, IndexType> TableCodebookDescReader<'a, CodeType, IndexType> {
 424     /// Constructs a new `TableCodebookDescReader` instance.
 425     pub fn new(codes: &'a [CodeType], bits: &'a [u8], idx_map: fn(usize) -> IndexType) -> Self {
 426         Self { bits, codes, idx_map }
 427     }
 428 }
 429 impl<'a, CodeType: Copy+Into<u32>, IndexType> CodebookDescReader<IndexType> for TableCodebookDescReader<'a, CodeType, IndexType>
 430 {
 431     fn bits(&mut self, idx: usize) -> u8  { self.bits[idx] }
 432     fn code(&mut self, idx: usize) -> u32 { self.codes[idx].into() }
 433     fn sym (&mut self, idx: usize) -> IndexType { (self.idx_map)(idx) }
 434     fn len(&mut self) -> usize { self.bits.len() }
 435 }
 436
 437 #[cfg(test)]
 438 mod test {
 439     use super::*;
 440     use crate::io::bitreader::*;
 441
 442     #[test]
 443     fn test_cb() {
 444         const BITS: [u8; 2] = [0b01011011, 0b10111100];
 445         let cb_desc: Vec<FullCodebookDesc<i8>> = vec!(
 446             FullCodebookDesc { code: 0b0,    bits: 1, sym:  16 },
 447             FullCodebookDesc { code: 0b10,   bits: 2, sym:  -3 },
 448             FullCodebookDesc { code: 0b110,  bits: 3, sym:  42 },
 449             FullCodebookDesc { code: 0b1110, bits: 4, sym: -42 }
 450         );
 451         let buf = &BITS;
 452         let mut br = BitReader::new(buf, BitReaderMode::BE);
 453         let mut cfr = FullCodebookDescReader::new(cb_desc);
 454         let cb = Codebook::new(&mut cfr, CodebookMode::MSB).unwrap();
 455         assert_eq!(br.read_cb(&cb).unwrap(),  16);
 456         assert_eq!(br.read_cb(&cb).unwrap(),  -3);
 457         assert_eq!(br.read_cb(&cb).unwrap(),  42);
 458         assert_eq!(br.read_cb(&cb).unwrap(), -42);
 459         let ret = br.read_cb(&cb);
 460         if let Err(e) = ret {
 461             assert_eq!(e as i32, CodebookError::InvalidCode as i32);
 462         } else {
 463             assert_eq!(0, 1);
 464         }
 465
 466         let scb_desc: Vec<ShortCodebookDesc> = vec!(
 467             ShortCodebookDesc { code: 0b0,    bits: 1 },
 468             ShortCodebookDesc { code: 0,      bits: 0 },
 469             ShortCodebookDesc { code: 0b10,   bits: 2 },
 470             ShortCodebookDesc { code: 0,      bits: 0 },
 471             ShortCodebookDesc { code: 0,      bits: 0 },
 472             ShortCodebookDesc { code: 0b110,  bits: 3 },
 473             ShortCodebookDesc { code: 0,      bits: 0 },
 474             ShortCodebookDesc { code: 0b11100, bits: 5 },
 475             ShortCodebookDesc { code: 0b11101, bits: 5 },
 476             ShortCodebookDesc { code: 0b1111010, bits: 7 },
 477             ShortCodebookDesc { code: 0b1111011, bits: 7 },
 478             ShortCodebookDesc { code: 0b1111110, bits: 7 },
 479             ShortCodebookDesc { code: 0b11111111, bits: 8 }
 480         );
 481         let mut br2 = BitReader::new(buf, BitReaderMode::BE);
 482         let mut cfr = ShortCodebookDescReader::new(scb_desc);
 483         let cb = Codebook::new(&mut cfr, CodebookMode::MSB).unwrap();
 484         assert_eq!(br2.read_cb(&cb).unwrap(), 0);
 485         assert_eq!(br2.read_cb(&cb).unwrap(), 2);
 486         assert_eq!(br2.read_cb(&cb).unwrap(), 5);
 487         assert_eq!(br2.read_cb(&cb).unwrap(), 8);
 488
 489         assert_eq!(reverse_bits(0b0000_0101_1011_1011_1101_1111_0111_1111, 32),
 490                                 0b1111_1110_1111_1011_1101_1101_1010_0000);
 491
 492         const BITS_LE: [u8; 3] = [0b11101111, 0b01110010, 0b01];
 493         let buf = &BITS_LE;
 494         let scble_desc: Vec<ShortCodebookDesc> = vec!(
 495             ShortCodebookDesc { code: 0b00,   bits: 2 },
 496             ShortCodebookDesc { code: 0,      bits: 0 },
 497             ShortCodebookDesc { code: 0b01,   bits: 2 },
 498             ShortCodebookDesc { code: 0,      bits: 0 },
 499             ShortCodebookDesc { code: 0,      bits: 0 },
 500             ShortCodebookDesc { code: 0b011,  bits: 3 },
 501             ShortCodebookDesc { code: 0,      bits: 0 },
 502             ShortCodebookDesc { code: 0b10111, bits: 5 },
 503             ShortCodebookDesc { code: 0b00111, bits: 5 },
 504             ShortCodebookDesc { code: 0b0101111, bits: 7 },
 505             ShortCodebookDesc { code: 0b0111111, bits: 7 },
 506             ShortCodebookDesc { code: 0b1011101111, bits: 10 }
 507         );
 508         let mut brl = BitReader::new(buf, BitReaderMode::LE);
 509         let mut cfr = ShortCodebookDescReader::new(scble_desc);
 510         let cb = Codebook::new(&mut cfr, CodebookMode::LSB).unwrap();
 511         assert_eq!(brl.read_cb(&cb).unwrap(), 11);
 512         assert_eq!(brl.read_cb(&cb).unwrap(), 0);
 513         assert_eq!(brl.read_cb(&cb).unwrap(), 7);
 514         assert_eq!(brl.read_cb(&cb).unwrap(), 0);
 515     }
 516 }