/* Delta.c -- Delta converter

2009-05-26 : Igor Pavlov : Public domain */

#include "Precomp.h"

#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);

}