1/* Delta.c -- Delta converter
22009-05-26 : Igor Pavlov : Public domain */
3
4#include "Delta.h"
5
6void Delta_Init(Byte *state)
7{
8  unsigned i;
9  for (i = 0; i < DELTA_STATE_SIZE; i++)
10    state[i] = 0;
11}
12
13static void MyMemCpy(Byte *dest, const Byte *src, unsigned size)
14{
15  unsigned i;
16  for (i = 0; i < size; i++)
17    dest[i] = src[i];
18}
19
20void Delta_Encode(Byte *state, unsigned delta, Byte *data, SizeT size)
21{
22  Byte buf[DELTA_STATE_SIZE];
23  unsigned j = 0;
24  MyMemCpy(buf, state, delta);
25  {
26    SizeT i;
27    for (i = 0; i < size;)
28    {
29      for (j = 0; j < delta && i < size; i++, j++)
30      {
31        Byte b = data[i];
32        data[i] = (Byte)(b - buf[j]);
33        buf[j] = b;
34      }
35    }
36  }
37  if (j == delta)
38    j = 0;
39  MyMemCpy(state, buf + j, delta - j);
40  MyMemCpy(state + delta - j, buf, j);
41}
42
43void Delta_Decode(Byte *state, unsigned delta, Byte *data, SizeT size)
44{
45  Byte buf[DELTA_STATE_SIZE];
46  unsigned j = 0;
47  MyMemCpy(buf, state, delta);
48  {
49    SizeT i;
50    for (i = 0; i < size;)
51    {
52      for (j = 0; j < delta && i < size; i++, j++)
53      {
54        buf[j] = data[i] = (Byte)(buf[j] + data[i]);
55      }
56    }
57  }
58  if (j == delta)
59    j = 0;
60  MyMemCpy(state, buf + j, delta - j);
61  MyMemCpy(state + delta - j, buf, j);
62}
63