Class DecodeTable

Libraries/unrar/unpack.hpp:31–70

Decode compressed bit fields to alphabet numbers.

// Decode compressed bit fields to alphabet numbers.
struct DecodeTable:PackDef
{
  // Real size of DecodeNum table.
  uint MaxNum;

  // Left aligned start and upper limit codes defining code space 
  // ranges for bit lengths. DecodeLen[BitLength-1] defines the start of
  // range for bit length and DecodeLen[BitLength] defines next code
  // after the end of range or in other words the upper limit code
  // for specified bit length.
  uint DecodeLen[16]; 

  // Every item of this array contains the sum of all preceding items.
  // So it contains the start position in code list for every bit length. 
  uint DecodePos[16];

  // Number of compressed bits processed in quick mode.
  // Must not exceed MAX_QUICK_DECODE_BITS.
  uint QuickBits;

  // Translates compressed bits (up to QuickBits length)
  // to bit length in quick mode.
  byte QuickLen[1<<MAX_QUICK_DECODE_BITS];

  // Translates compressed bits (up to QuickBits length)
  // to position in alphabet in quick mode.
  // 'ushort' saves some memory and even provides a little speed gain
  // comparting to 'uint' here.
  ushort QuickNum[1<<MAX_QUICK_DECODE_BITS];

  // Translate the position in code list to position in alphabet.
  // We do not allocate it dynamically to avoid performance overhead
  // introduced by pointer, so we use the largest possible table size
  // as array dimension. Real size of this array is defined in MaxNum.
  // We use this array if compressed bit field is too lengthy
  // for QuickLen based translation.
  // 'ushort' saves some memory and even provides a little speed gain
  // comparting to 'uint' here.
  ushort DecodeNum[LARGEST_TABLE_SIZE];
};


struct UnpackBlockHeader