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