/* Delta.c -- Delta converter
 2009-05-26 : Igor Pavlov : Public domain */
 
 #include "Delta.h"
 
 void Delta_Init(Byte *state)
 {
   unsigned i;
   for (i = 0; i < DELTA_STATE_SIZE; i++)
     state[i] = 0;
 }
 
 static void MyMemCpy(Byte *dest, const Byte *src, unsigned size)
 {
   unsigned i;
   for (i = 0; i < size; i++)
     dest[i] = src[i];
 }
 
 void Delta_Encode(Byte *state, unsigned delta, Byte *data, SizeT size)
 {
   Byte buf[DELTA_STATE_SIZE];
   unsigned j = 0;
   MyMemCpy(buf, state, delta);
   {
     SizeT i;
     for (i = 0; i < size;)
     {
       for (j = 0; j < delta && i < size; i++, j++)
       {
         Byte b = data[i];
         data[i] = (Byte)(b - buf[j]);
         buf[j] = b;
       }
     }
   }
   if (j == delta)
     j = 0;
   MyMemCpy(state, buf + j, delta - j);
   MyMemCpy(state + delta - j, buf, j);
 }
 
 void Delta_Decode(Byte *state, unsigned delta, Byte *data, SizeT size)
 {
   Byte buf[DELTA_STATE_SIZE];
   unsigned j = 0;
   MyMemCpy(buf, state, delta);
   {
     SizeT i;
     for (i = 0; i < size;)
     {
       for (j = 0; j < delta && i < size; i++, j++)
       {
         buf[j] = data[i] = (Byte)(buf[j] + data[i]);
       }
     }
   }
   if (j == delta)
     j = 0;
   MyMemCpy(state, buf + j, delta - j);
   MyMemCpy(state + delta - j, buf, j);
 }