Bit operations-set-get-xor-rotate on bits arrays
Wed Jan 23, 2013 1:07 am
Bit operations - set-get-xor-rotate functions
cpp code
Usage example of this bit functions
cpp code
Bit.h
cpp code
Code author
cpp code
/*****************************************************************************
* *
* --------------------------------- bit.c -------------------------------- *
* *
*****************************************************************************/
#include <string.h>
#include "bit.h"
/*****************************************************************************
* *
* -------------------------------- 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 %; i++)
mask = mask >> 1;
/*****************************************************************************
* *
* Get the bit. *
* *
*****************************************************************************/
return (((mask & bits[(int)(pos /
}
/*****************************************************************************
* *
* -------------------------------- 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 %
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) /
/********************************************************************
* *
* 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);
}
/********************************************************************
* *
* Shift the current byte to the left. *
* *
********************************************************************/
bits[i] = bits[i] << 1;
}
/***********************************************************************
* *
* Set the rightmost bit of the buffer to the bit shifted off the *
* first byte. *
* *
***********************************************************************/
bit_set(bits, size - 1, fbit);
}
}
return;
}
Usage example of this bit functions
cpp code
#include <stdio.h>
#include <string.h>
#include "bit.h"
/*****************************************************************************
* *
* --------------------------------- main --------------------------------- *
* *
*****************************************************************************/
int main(int argc, char **argv) {
unsigned char bits1[8],
bits2[8],
bits3[8];
int i;
/*****************************************************************************
* *
* Perform some bit operations using 64-bit buffers. *
* *
*****************************************************************************/
for (i = 0; i < 8; i++) {
bits1[i] = 0x00;
bits2[i] = 0x00;
bits3[i] = 0x00;
}
fprintf(stdout, "Initially\n");
fprintf(stdout, "bits1: %02x %02x %02x %02x %02x %02x %02x %02x\n", bits1[0],
bits1[1], bits1[2], bits1[3], bits1[4], bits1[5], bits1[6], bits1[7]);
fprintf(stdout, "bits2: %02x %02x %02x %02x %02x %02x %02x %02x\n", bits2[0],
bits2[1], bits2[2], bits2[3], bits2[4], bits2[5], bits2[6], bits2[7]);
bit_set(bits1, 15, 1);
bit_set(bits1, 16, 1);
bit_set(bits1, 32, 1);
bit_set(bits1, 63, 1);
bit_set(bits2, 0, 1);
bit_set(bits2, 15, 1);
fprintf(stdout, "After setting bits 15, 16, 32, 63 of bits1 and bits 00, 15 "
"of bits2\n");
fprintf(stdout, "bits1: %02x %02x %02x %02x %02x %02x %02x %02x\n", bits1[0],
bits1[1], bits1[2], bits1[3], bits1[4], bits1[5], bits1[6], bits1[7]);
fprintf(stdout, "bits2: %02x %02x %02x %02x %02x %02x %02x %02x\n", bits2[0],
bits2[1], bits2[2], bits2[3], bits2[4], bits2[5], bits2[6], bits2[7]);
fprintf(stdout, "Bit 63 of bits1 is %d\n", bit_get(bits1, 63));
fprintf(stdout, "Bit 62 of bits1 is %d\n", bit_get(bits1, 62));
fprintf(stdout, "Bit 00 of bits2 is %d\n", bit_get(bits2, 0));
fprintf(stdout, "Bit 01 of bits2 is %d\n", bit_get(bits2, 1));
bit_xor(bits1, bits2, bits3, 32);
fprintf(stdout, "bits3 is bits1 XOR bits2 (32 bits)\n");
fprintf(stdout, "bits3: %02x %02x %02x %02x %02x %02x %02x %02x\n", bits3[0],
bits3[1], bits3[2], bits3[3], bits3[4], bits3[5], bits3[6], bits3[7]);
bit_xor(bits1, bits2, bits3, 64);
fprintf(stdout, "bits3 is bits1 XOR bits2 (64 bits)\n");
fprintf(stdout, "bits3: %02x %02x %02x %02x %02x %02x %02x %02x\n", bits3[0],
bits3[1], bits3[2], bits3[3], bits3[4], bits3[5], bits3[6], bits3[7]);
bit_rot_left(bits1, 64, 1);
fprintf(stdout, "After rotating bits1 left x 1 (64 bits)\n");
fprintf(stdout, "bits1: %02x %02x %02x %02x %02x %02x %02x %02x\n", bits1[0],
bits1[1], bits1[2], bits1[3], bits1[4], bits1[5], bits1[6], bits1[7]);
bit_rot_left(bits2, 64, 1);
fprintf(stdout, "After rotating bits2 left x 1 (64 bits)\n");
fprintf(stdout, "bits2: %02x %02x %02x %02x %02x %02x %02x %02x\n", bits2[0],
bits2[1], bits2[2], bits2[3], bits2[4], bits2[5], bits2[6], bits2[7]);
bit_rot_left(bits2, 16, 7);
fprintf(stdout, "After rotating bits2 left x 7 (16 bits)\n");
fprintf(stdout, "bits2: %02x %02x %02x %02x %02x %02x %02x %02x\n", bits2[0],
bits2[1], bits2[2], bits2[3], bits2[4], bits2[5], bits2[6], bits2[7]);
bit_rot_left(bits2, 8, 2);
fprintf(stdout, "After rotating bits2 left x 2 (8 bits)\n");
fprintf(stdout, "bits2: %02x %02x %02x %02x %02x %02x %02x %02x\n", bits2[0],
bits2[1], bits2[2], bits2[3], bits2[4], bits2[5], bits2[6], bits2[7]);
for (i = 0; i < 8; i++) {
bits2[i] = 0x00;
}
bit_set(bits2, 0, 1);
bit_set(bits2, 3, 1);
bit_set(bits2, 8, 1);
bit_set(bits2, 27, 1);
fprintf(stdout, "After clearing and setting bits 0, 3, 8, 27 of bits2\n");
fprintf(stdout, "bits2: %02x %02x %02x %02x %02x %02x %02x %02x\n", bits2[0],
bits2[1], bits2[2], bits2[3], bits2[4], bits2[5], bits2[6], bits2[7]);
bit_rot_left(bits2, 11, 6);
fprintf(stdout, "After rotating bits2 left x 6 (11 bits)\n");
fprintf(stdout, "bits2: %02x %02x %02x %02x %02x %02x %02x %02x\n", bits2[0],
bits2[1], bits2[2], bits2[3], bits2[4], bits2[5], bits2[6], bits2[7]);
for (i = 0; i < 8; i++) {
bits2[i] = 0x00;
}
bit_set(bits2, 0, 1);
bit_set(bits2, 3, 1);
bit_set(bits2, 8, 1);
bit_set(bits2, 27, 1);
fprintf(stdout, "After clearing and setting bits 0, 3, 8, 27 of bits2\n");
fprintf(stdout, "bits2: %02x %02x %02x %02x %02x %02x %02x %02x\n", bits2[0],
bits2[1], bits2[2], bits2[3], bits2[4], bits2[5], bits2[6], bits2[7]);
bit_rot_left(bits2, 28, 4);
fprintf(stdout, "After rotating bits2 left x 4 (28 bits)\n");
fprintf(stdout, "bits2: %02x %02x %02x %02x %02x %02x %02x %02x\n", bits2[0],
bits2[1], bits2[2], bits2[3], bits2[4], bits2[5], bits2[6], bits2[7]);
return 0;
}
Bit.h
cpp code
/*****************************************************************************
* *
* --------------------------------- bit.h -------------------------------- *
* *
*****************************************************************************/
#ifndef BIT_H
#define BIT_H
/*****************************************************************************
* *
* --------------------------- Public Interface --------------------------- *
* *
*****************************************************************************/
int bit_get(const unsigned char *bits, int pos);
void bit_set(unsigned char *bits, int pos, int state);
void bit_xor(const unsigned char *bits1, const unsigned char *bits2, unsigned
char *bitsx, int size);
void bit_rot_left(unsigned char *bits, int size, int count);
#endif
Code author
- Code:
"Mastering Algorithms with C" by Kyle Loudon
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