1 /* Delta.c -- Delta converter 2 2009-05-26 : Igor Pavlov : Public domain */ 3 4 #include "Delta.h" 5 6 void Delta_Init(Byte *state) 7 { 8 unsigned i; 9 for (i = 0; i < DELTA_STATE_SIZE; i++) 10 state[i] = 0; 11 } 12 13 static 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 20 void 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 43 void 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
