clr.cdr

/*
 * Note it is up to the calling code to ensure that no overruns on input and
 * output buffers occur.
 *
 * Call the input() and output() functions to set and query the current
 * buffer locations.
 */

#define  DO(n)	   for (int _=0; _<n; _++)
#define  TOP	   (1<<24)

#define CodecName "CLR"

typedef unsigned char uc;

class RangeCoder
{
    uint64_t low;
    uint  range, code;

public:

 uc *in_buf;
 uc *out_buf;

 void input (char *in)  { out_buf = in_buf = (uc *)in;  }
 void output(char *out) { in_buf = out_buf = (uc *)out; }
 char *input(void)  {return (char *)in_buf;}
 char *output(void) {return (char *)out_buf;}
 int size_out(void) {return out_buf - in_buf;}
 int size_in(void)  {return in_buf - out_buf;}

 void StartEncode ( void )    
 { 
   low=0;  
   range=(uint)-1; 
 }

 void StartDecode( void )    
 { 
   code = low=0;  
   range=(uint)-1;
   DO(8) code = (code<<8) | *in_buf++;
 }

 void FinishEncode( void ) 
 { 
     DO(8) (*out_buf++ = low>>56), low<<=8; 
 }

 void FinishDecode( void ) {}

 void Encode (uint cumFreq, uint freq, uint totFreq) 
 {
     low  += cumFreq * (range/= totFreq);
     range*= freq;

     if (cumFreq + freq > totFreq)
	 abort();

     while( range<TOP ) {
	 // range = 0x00ffffff..
	 // low/high may be matching
	 //       eg 88332211/88342211 (range 00010000)
	 // or differing
	 //       eg 88ff2211/89002211 (range 00010000)
	 //
	 // If the latter, we need to reduce range down
	 // such that high=88ffffff.
	 // Eg. top-1      == 00ffffff
	 //     low|top-1  == 88ffffff
	 //     ...-low    == 0000ddee
	 if ( uc((low^(low+range))>>56) ) 
	     range = ((uint(low)|(TOP-1))-uint(low));
	 *out_buf++ = low>>56, range<<=8, low<<=8;
     }
 }

 uint GetFreq (uint totFreq) {
     return code/(range/=totFreq);
 }

 void Decode (uint cumFreq, uint freq, uint totFreq) 
 {
   uint temp = cumFreq*range;
   low  += temp;
   code -= temp;
   range*= freq;
 
   while( range<TOP ) {
       if ( uc((low^(low+range))>>56) ) 
	   range = ((uint(low)|(TOP-1))-uint(low));
       code = (code<<8) | *in_buf++, range<<=8, low<<=8;
   }
 }

};