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/* 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);
}