Mastering Algorithms With C - Kyle Loudon [159]
/*****************************************************************************
* *
* -------------------------------- bit_get ------------------------------- *
* *
*****************************************************************************/
int bit_get(const unsigned char *bits, int pos) {
unsigned char mask;
int i;
/*****************************************************************************
* *
* Set a mask for the bit to get. *
* *
*****************************************************************************/
mask = 0x80;
for (i = 0; i < (pos % 8); i++)
mask = mask >> 1;
/*****************************************************************************
* *
* Get the bit. *
* *
*****************************************************************************/
return (((mask & bits[(int)(pos / 8)]) == mask) ? 1 : 0);
}
/*****************************************************************************
* *
* -------------------------------- bit_set ------------------------------- *
* *
*****************************************************************************/
void bit_set(unsigned char *bits, int pos, int state) {
unsigned char mask;
int i;
/*****************************************************************************
* *
* Set a mask for the bit to set. *
* *
*****************************************************************************/
mask = 0x80;
for (i = 0; i < (pos % 8); i++)
mask = mask >> 1;
/*****************************************************************************
* *
* Set the bit. *
* *
*****************************************************************************/
if (state)
bits[pos / 8] = bits[pos / 8] | mask;
else
bits[pos / 8] = bits[pos / 8] & (~mask);
return;
}
/*****************************************************************************
* *
* -------------------------------- bit_xor ------------------------------- *
* *
*****************************************************************************/
void bit_xor(const unsigned char *bits1, const unsigned char *bits2, unsigned
char *bitsx, int size) {
int i;
/*****************************************************************************
* *
* Compute the bitwise XOR (exclusive OR) of the two buffers. *
* *
*****************************************************************************/
for (i = 0; i < size; i++) {
if (bit_ get(bits1, i) != bit_ get(bits2, i))
bit_set(bitsx, i, 1);
else
bit_set(bitsx, i, 0);
}
return;
}
/*****************************************************************************
* *
* ----------------------------- bit_rot_left ----------------------------- *
* *
*****************************************************************************/
void bit_rot_left(unsigned char *bits, int size, int count) {
int fbit,
lbit,
i,
j;
/*****************************************************************************
* *
* Rotate the buffer to the left the specified number of bits. *
* *
*****************************************************************************/
if (size > 0) {
for (j = 0; j < count; j++) {
for (i = 0; i <= ((size - 1) / 8); i++) {
/********************************************************************
* *
* Get the bit about to be shifted off the current byte. *
* *
********************************************************************/
lbit = bit_get(&bits[i], 0);
if (i == 0) {
/*****************************************************************
* *
* Save the bit shifted off the first byte for later. *
* *
*****************************************************************/
fbit = lbit;
}
else {
/*****************************************************************
* *
* Set the rightmost bit of the previous byte to the leftmost *
* bit about to be shifted off the current byte. *
* *
*****************************************************************/
bit_set(&bits[i - 1], 7, lbit);
}
/********************************************************************