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::MSB).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     pub table: Vec<u32>,
 131     pub syms:  Vec<S>,
 132     pub 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 pub 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) -> CodebookResult<()> {
 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             if table[idx + off] != TABLE_FILL_VALUE { return Err(CodebookError::InvalidCodebook); }
 156             table[idx + off] = lut_value;
 157         }
 158     } else {
 159         let idx = (code as usize) + off;
 160         if table[idx] != TABLE_FILL_VALUE { return Err(CodebookError::InvalidCodebook); }
 161         table[idx] = (symidx << 8) | 0x80 | u32::from(bits);
 162     }
 163     Ok(())
 164 }
 165
 166 fn fill_lut_lsb(table: &mut Vec<u32>, off: usize,
 167                 code: u32, bits: u8, lut_bits: u8, symidx: u32, esc: bool) -> CodebookResult<()> {
 168     if !esc {
 169         let fill_len  = lut_bits - bits;
 170         let fill_size = 1 << fill_len;
 171         let fill_code = code;
 172         let step = lut_bits - fill_len;
 173         for j in 0..fill_size {
 174             let idx = (fill_code + (j << step)) as usize;
 175             if table[idx + off] != TABLE_FILL_VALUE { return Err(CodebookError::InvalidCodebook); }
 176             table[idx + off] = (symidx << 8) | u32::from(bits);
 177         }
 178     } else {
 179         let idx = (code as usize) + off;
 180         if table[idx] != TABLE_FILL_VALUE { return Err(CodebookError::InvalidCodebook); }
 181         table[idx] = (symidx << 8) | 0x80 | u32::from(bits);
 182     }
 183     Ok(())
 184 }
 185
 186 fn fill_lut(table: &mut Vec<u32>, mode: CodebookMode,
 187             off: usize, code: u32, bits: u8, lut_bits: u8, symidx: u32, esc: bool) -> CodebookResult<bool> {
 188     match mode {
 189         CodebookMode::MSB => fill_lut_msb(table, off, code, bits, lut_bits, symidx, esc)?,
 190         CodebookMode::LSB => fill_lut_lsb(table, off, code, bits, lut_bits, symidx, esc)?,
 191     };
 192     Ok(bits > lut_bits)
 193 }
 194
 195 fn resize_table(table: &mut Vec<u32>, bits: u8) -> CodebookResult<u32> {
 196     let add_size = (1 << bits) as usize;
 197     table.reserve(add_size);
 198     let cur_off = table.len() as u32;
 199     let new_size = table.len() + add_size;
 200     if table.capacity() < new_size { return Err(CodebookError::MemoryError); }
 201     table.resize(new_size, TABLE_FILL_VALUE);
 202     Ok(cur_off)
 203 }
 204
 205
 206 fn extract_lut_part(code: u32, bits: u8, lut_bits: u8, mode: CodebookMode) -> u32 {
 207     match mode {
 208         CodebookMode::MSB => code >> (bits - lut_bits),
 209         CodebookMode::LSB => code & ((1 << lut_bits) - 1),
 210     }
 211 }
 212
 213 fn extract_esc_part(code: u32, bits: u8, lut_bits: u8, mode: CodebookMode) -> u32 {
 214     match mode {
 215         CodebookMode::MSB => code & ((1 << (bits - lut_bits)) - 1),
 216         CodebookMode::LSB => code >> lut_bits,
 217     }
 218 }
 219
 220 #[derive(Clone,Copy)]
 221 struct Code {
 222     code: u32,
 223     bits: u8,
 224     idx:  usize,
 225 }
 226
 227 struct CodeBucket {
 228     maxlen: u8,
 229     offset: usize,
 230     codes:  Vec<Code>,
 231 }
 232
 233 impl CodeBucket {
 234     fn new() -> Self {
 235         CodeBucket { maxlen: 0, offset: 0, codes: Vec::new() }
 236     }
 237     fn add_code(&mut self, c: Code) {
 238         if c.bits > self.maxlen { self.maxlen = c.bits; }
 239         self.codes.push(c);
 240     }
 241 }
 242
 243 type EscapeCodes = HashMap<u32, CodeBucket>;
 244
 245 fn add_esc_code(cc: &mut EscapeCodes, key: u32, code: u32, bits: u8, idx: usize) {
 246     cc.entry(key).or_insert_with(CodeBucket::new);
 247     let b = cc.get_mut(&key);
 248     if let Some(bucket) = b {
 249         bucket.add_code(Code {code, bits, idx });
 250     } else { panic!("no bucket when expected!"); }
 251 }
 252
 253 fn build_esc_lut(table: &mut Vec<u32>,
 254                  mode: CodebookMode,
 255                  bucket: &CodeBucket) -> CodebookResult<()> {
 256     let mut escape_list: EscapeCodes = HashMap::new();
 257     let maxlen = if bucket.maxlen > MAX_LUT_BITS { MAX_LUT_BITS } else { bucket.maxlen };
 258
 259     for code in &bucket.codes {
 260         let bits = code.bits;
 261         if code.bits <= MAX_LUT_BITS {
 262             fill_lut(table, mode, bucket.offset, code.code, bits,
 263                      maxlen, code.idx as u32, false)?;
 264         } else {
 265             let ckey = extract_lut_part(code.code, bits, MAX_LUT_BITS, mode);
 266             let cval = extract_esc_part(code.code, bits, MAX_LUT_BITS, mode);
 267             add_esc_code(&mut escape_list, ckey, cval, bits - MAX_LUT_BITS, code.idx);
 268         }
 269     }
 270
 271     let cur_offset = bucket.offset;
 272     for (ckey, sec_bucket) in &mut escape_list {
 273         let key = *ckey as u32;
 274         let maxlen = min(sec_bucket.maxlen, MAX_LUT_BITS);
 275         let new_off = resize_table(table, maxlen)?;
 276         fill_lut(table, mode, cur_offset, key, maxlen,
 277                  MAX_LUT_BITS, new_off, true)?;
 278         sec_bucket.offset = new_off as usize;
 279     }
 280
 281     for sec_bucket in escape_list.values() {
 282         build_esc_lut(table, mode, sec_bucket)?;
 283     }
 284
 285     Ok(())
 286 }
 287
 288 impl<S: Copy> Codebook<S> {
 289
 290     /// Constructs a new `Codebook` instance using provided codebook description and mode.
 291     pub fn new(cb: &mut CodebookDescReader<S>, mode: CodebookMode) -> CodebookResult<Self> {
 292         let mut maxbits = 0;
 293         let mut nnz = 0;
 294         let mut escape_list: EscapeCodes = HashMap::new();
 295
 296         let mut symidx: usize = 0;
 297         for i in 0..cb.len() {
 298             let bits = cb.bits(i);
 299             if bits > 0 {
 300                 nnz += 1;
 301                 if cb.code(i) >= (1 << bits) {
 302                     return Err(CodebookError::InvalidCodebook);
 303                 }
 304             }
 305             maxbits = max(bits, maxbits);
 306             if bits > MAX_LUT_BITS {
 307                 let code = cb.code(i);
 308                 let ckey = extract_lut_part(code, bits, MAX_LUT_BITS, mode);
 309                 let cval = extract_esc_part(code, bits, MAX_LUT_BITS, mode);
 310                 add_esc_code(&mut escape_list, ckey, cval, bits - MAX_LUT_BITS, symidx);
 311             }
 312             if bits > 0 { symidx += 1; }
 313         }
 314         if maxbits == 0 { return Err(CodebookError::InvalidCodebook); }
 315
 316         if maxbits > MAX_LUT_BITS { maxbits = MAX_LUT_BITS; }
 317
 318         let tab_len = 1 << maxbits;
 319         let mut table: Vec<u32> = Vec::with_capacity(tab_len);
 320         let mut syms:  Vec<S>   = Vec::with_capacity(nnz);
 321         if table.capacity() < tab_len { return Err(CodebookError::MemoryError); }
 322         if syms.capacity()  < nnz     { return Err(CodebookError::MemoryError); }
 323         table.resize(tab_len, TABLE_FILL_VALUE);
 324
 325         let mut symidx: u32 = 0;
 326         for i in 0..cb.len() {
 327             let bits = cb.bits(i);
 328             let code = cb.code(i);
 329             if bits == 0 { continue; }
 330             if bits <= MAX_LUT_BITS {
 331                 fill_lut(&mut table, mode, 0, code, bits, maxbits, symidx, false)?;
 332             } else {
 333                 let ckey = extract_lut_part(code, bits, MAX_LUT_BITS, mode) as usize;
 334                 if table[ckey] == TABLE_FILL_VALUE {
 335                     let key = ckey as u32;
 336                     if let Some(bucket) = escape_list.get_mut(&key) {
 337                         let maxlen = min(bucket.maxlen, MAX_LUT_BITS);
 338                         let new_off = resize_table(&mut table, maxlen)?;
 339                         fill_lut(&mut table, mode, 0, key, maxlen, MAX_LUT_BITS, new_off, true)?;
 340                         bucket.offset = new_off as usize;
 341                     }
 342                 }
 343             }
 344             symidx += 1;
 345         }
 346
 347         for bucket in escape_list.values() {
 348             build_esc_lut(&mut table, mode, &bucket)?;
 349         }
 350
 351         for i in 0..cb.len() {
 352             if cb.bits(i) > 0 {
 353                 syms.push(cb.sym(i));
 354             }
 355         }
 356
 357         Ok(Codebook { table, syms, lut_bits: maxbits })
 358     }
 359 }
 360
 361 impl<'a, S: Copy> CodebookReader<S> for BitReader<'a> {
 362     #[allow(unused_variables)]
 363     fn read_cb(&mut self, cb: &Codebook<S>) -> CodebookResult<S> {
 364         let mut esc = true;
 365         let mut idx = 0;
 366         let mut lut_bits = cb.lut_bits;
 367         while esc {
 368             let lut_idx = (self.peek(lut_bits) as usize) + (idx as usize);
 369             if cb.table[lut_idx] == TABLE_FILL_VALUE { return Err(CodebookError::InvalidCode); }
 370             let bits = cb.table[lut_idx] & 0x7F;
 371             esc  = (cb.table[lut_idx] & 0x80) != 0;
 372             idx  = (cb.table[lut_idx] >> 8) as usize;
 373             if (bits as isize) > self.left() {
 374                 return Err(CodebookError::InvalidCode);
 375             }
 376             let skip_bits = if esc { u32::from(lut_bits) } else { bits };
 377             self.skip(skip_bits as u32).unwrap();
 378             lut_bits = bits as u8;
 379         }
 380         Ok(cb.syms[idx])
 381     }
 382 }
 383
 384 /// Codebook description that stores a list of codewords and their values.
 385 pub struct FullCodebookDescReader<S> {
 386     data: Vec<FullCodebookDesc<S>>,
 387 }
 388
 389 impl<S> FullCodebookDescReader<S> {
 390     /// Constructs a new `FullCodebookDescReader` instance.
 391     pub fn new(data: Vec<FullCodebookDesc<S>>) -> Self {
 392         FullCodebookDescReader { data }
 393     }
 394 }
 395
 396 impl<S: Copy> CodebookDescReader<S> for FullCodebookDescReader<S> {
 397     fn bits(&mut self, idx: usize) -> u8  { self.data[idx].bits }
 398     fn code(&mut self, idx: usize) -> u32 { self.data[idx].code }
 399     fn sym (&mut self, idx: usize) -> S   { self.data[idx].sym  }
 400     fn len(&mut self) -> usize { self.data.len() }
 401 }
 402
 403 /// Codebook description that stores a list of codewords and their value is equal to the index.
 404 pub struct ShortCodebookDescReader {
 405     data: Vec<ShortCodebookDesc>,
 406 }
 407
 408 impl ShortCodebookDescReader {
 409     /// Constructs a new `ShortCodebookDescReader` instance.
 410     pub fn new(data: Vec<ShortCodebookDesc<>>) -> Self {
 411         ShortCodebookDescReader { data }
 412     }
 413 }
 414
 415 impl CodebookDescReader<u32> for ShortCodebookDescReader {
 416     fn bits(&mut self, idx: usize) -> u8  { self.data[idx].bits }
 417     fn code(&mut self, idx: usize) -> u32 { self.data[idx].code }
 418     fn sym (&mut self, idx: usize) -> u32 { idx as u32 }
 419     fn len(&mut self) -> usize { self.data.len() }
 420 }
 421
 422 /// Flexible codebook description that uses two separate arrays for codeword bits and lengths and a function that maps codeword index into its symbol.
 423 pub struct TableCodebookDescReader<'a, CodeType:'static, IndexType:'static> {
 424     bits:       &'a [u8],
 425     codes:      &'a [CodeType],
 426     idx_map:    fn(usize) -> IndexType,
 427 }
 428
 429 impl<'a, CodeType, IndexType> TableCodebookDescReader<'a, CodeType, IndexType> {
 430     /// Constructs a new `TableCodebookDescReader` instance.
 431     pub fn new(codes: &'a [CodeType], bits: &'a [u8], idx_map: fn(usize) -> IndexType) -> Self {
 432         Self { bits, codes, idx_map }
 433     }
 434 }
 435 impl<'a, CodeType: Copy+Into<u32>, IndexType> CodebookDescReader<IndexType> for TableCodebookDescReader<'a, CodeType, IndexType>
 436 {
 437     fn bits(&mut self, idx: usize) -> u8  { self.bits[idx] }
 438     fn code(&mut self, idx: usize) -> u32 { self.codes[idx].into() }
 439     fn sym (&mut self, idx: usize) -> IndexType { (self.idx_map)(idx) }
 440     fn len(&mut self) -> usize { self.bits.len() }
 441 }
 442
 443 #[cfg(test)]
 444 mod test {
 445     use super::*;
 446     use crate::io::bitreader::*;
 447
 448     #[test]
 449     fn test_cb() {
 450         const BITS: [u8; 2] = [0b01011011, 0b10111100];
 451         let cb_desc: Vec<FullCodebookDesc<i8>> = vec!(
 452             FullCodebookDesc { code: 0b0,    bits: 1, sym:  16 },
 453             FullCodebookDesc { code: 0b10,   bits: 2, sym:  -3 },
 454             FullCodebookDesc { code: 0b110,  bits: 3, sym:  42 },
 455             FullCodebookDesc { code: 0b1110, bits: 4, sym: -42 }
 456         );
 457         let buf = &BITS;
 458         let mut br = BitReader::new(buf, BitReaderMode::BE);
 459         let mut cfr = FullCodebookDescReader::new(cb_desc);
 460         let cb = Codebook::new(&mut cfr, CodebookMode::MSB).unwrap();
 461         assert_eq!(br.read_cb(&cb).unwrap(),  16);
 462         assert_eq!(br.read_cb(&cb).unwrap(),  -3);
 463         assert_eq!(br.read_cb(&cb).unwrap(),  42);
 464         assert_eq!(br.read_cb(&cb).unwrap(), -42);
 465         let ret = br.read_cb(&cb);
 466         if let Err(e) = ret {
 467             assert_eq!(e as i32, CodebookError::InvalidCode as i32);
 468         } else {
 469             assert_eq!(0, 1);
 470         }
 471
 472         let scb_desc: Vec<ShortCodebookDesc> = vec!(
 473             ShortCodebookDesc { code: 0b0,    bits: 1 },
 474             ShortCodebookDesc { code: 0,      bits: 0 },
 475             ShortCodebookDesc { code: 0b10,   bits: 2 },
 476             ShortCodebookDesc { code: 0,      bits: 0 },
 477             ShortCodebookDesc { code: 0,      bits: 0 },
 478             ShortCodebookDesc { code: 0b110,  bits: 3 },
 479             ShortCodebookDesc { code: 0,      bits: 0 },
 480             ShortCodebookDesc { code: 0b11100, bits: 5 },
 481             ShortCodebookDesc { code: 0b11101, bits: 5 },
 482             ShortCodebookDesc { code: 0b1111010, bits: 7 },
 483             ShortCodebookDesc { code: 0b1111011, bits: 7 },
 484             ShortCodebookDesc { code: 0b1111110, bits: 7 },
 485             ShortCodebookDesc { code: 0b11111111, bits: 8 }
 486         );
 487         let mut br2 = BitReader::new(buf, BitReaderMode::BE);
 488         let mut cfr = ShortCodebookDescReader::new(scb_desc);
 489         let cb = Codebook::new(&mut cfr, CodebookMode::MSB).unwrap();
 490         assert_eq!(br2.read_cb(&cb).unwrap(), 0);
 491         assert_eq!(br2.read_cb(&cb).unwrap(), 2);
 492         assert_eq!(br2.read_cb(&cb).unwrap(), 5);
 493         assert_eq!(br2.read_cb(&cb).unwrap(), 8);
 494
 495         assert_eq!(reverse_bits(0b0000_0101_1011_1011_1101_1111_0111_1111, 32),
 496                                 0b1111_1110_1111_1011_1101_1101_1010_0000);
 497
 498         const BITS_LE: [u8; 3] = [0b11101111, 0b01110010, 0b01];
 499         let buf = &BITS_LE;
 500         let scble_desc: Vec<ShortCodebookDesc> = vec!(
 501             ShortCodebookDesc { code: 0b00,   bits: 2 },
 502             ShortCodebookDesc { code: 0,      bits: 0 },
 503             ShortCodebookDesc { code: 0b01,   bits: 2 },
 504             ShortCodebookDesc { code: 0,      bits: 0 },
 505             ShortCodebookDesc { code: 0,      bits: 0 },
 506             ShortCodebookDesc { code: 0b011,  bits: 3 },
 507             ShortCodebookDesc { code: 0,      bits: 0 },
 508             ShortCodebookDesc { code: 0b10111, bits: 5 },
 509             ShortCodebookDesc { code: 0b00111, bits: 5 },
 510             ShortCodebookDesc { code: 0b0101111, bits: 7 },
 511             ShortCodebookDesc { code: 0b0111111, bits: 7 },
 512             ShortCodebookDesc { code: 0b1011101111, bits: 10 }
 513         );
 514         let mut brl = BitReader::new(buf, BitReaderMode::LE);
 515         let mut cfr = ShortCodebookDescReader::new(scble_desc);
 516         let cb = Codebook::new(&mut cfr, CodebookMode::LSB).unwrap();
 517         assert_eq!(brl.read_cb(&cb).unwrap(), 11);
 518         assert_eq!(brl.read_cb(&cb).unwrap(), 0);
 519         assert_eq!(brl.read_cb(&cb).unwrap(), 7);
 520         assert_eq!(brl.read_cb(&cb).unwrap(), 0);
 521     }
 522 }