OpenBoard/src/pdf-merger/RunLengthDecode.cpp

#include "RunLengthDecode.h"

using namespace merge_lib;

/* The encoded data is a sequence of
runs, where each run consists of a length byte followed by 1 to 128 bytes of data. If
the length byte is in the range 0 to 127, the following length + 1 (1 to 128) bytes
are copied literally during decompression. If length is in the range 129 to 255, the
following single byte is to be copied 257 - length (2 to 128) times during decom-
pression. A length value of 128 denotes EOD.  */


// Function performs RunLength Decoder for PDF, very simple
bool RunLengthDecode::decode(std::string & encoded)
{
   std::string decoded;

   for(unsigned enci = 0;enci < encoded.size();)
   {
      unsigned char c = encoded[enci++];
      if( c == 128 )
      {
         break; //EOD
      }
      else if( c < 128 )
      {
         for(int j = 0; j < (c+1);j++)
         {
            decoded.append(1,encoded[enci]);
         }
         enci++;
      }
      else 
      {
         for(int j = 0; j < (257 - c);j++)
         {
            decoded.append(1,encoded[enci]);
         }
         enci++;
      }
   }
   return true;
}