Function ComputeRecoveryFileCount

src/libpar2.cpp:129–201

Determine how many recovery files to create.

// Determine how many recovery files to create.
bool ComputeRecoveryFileCount(std::ostream &sout,
			      std::ostream &serr,
			      u32 *recoveryfilecount,
			      Scheme recoveryfilescheme,
			      u32 recoveryblockcount,
			      u64 largestfilesize,
			      u64 blocksize)
{
  // Are we computing any recovery blocks
  if (recoveryblockcount == 0)
  {
    *recoveryfilecount = 0;
    return true;
  }

  switch (recoveryfilescheme)
  {
  case scUnknown:
    {
      //assert(false);
      serr << "Scheme unspecified (create, verify, or repair)." << std::endl;
      return false;
    }
    break;
  case scVariable:
  case scUniform:
    {
      if (*recoveryfilecount == 0)
      {
        // If none specified then then filecount is roughly log2(blockcount)
        // This prevents you getting excessively large numbers of files
        // when the block count is high and also allows the files to have
        // sizes which vary exponentially.

        for (u32 blocks=recoveryblockcount; blocks>0; blocks>>=1)
        {
          (*recoveryfilecount)++;
        }
      }

      if (*recoveryfilecount > recoveryblockcount)
      {
        // You cannot have more recovery files than there are recovery blocks
        // to put in them.
        serr << "Too many recovery files specified." << std::endl;
        return false;
      }
    }
    break;

  case scLimited:
    {
      // No recovery file will contain more recovery blocks than would
      // be required to reconstruct the largest source file if it
      // were missing. Other recovery files will have recovery blocks
      // distributed in an exponential scheme.

      u32 largest = (u32)((largestfilesize + blocksize-1) / blocksize);