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This program shows a logic of swapping the most significant bit with the least significant bit, second most significant bit with the second least significant bit, and so on.

/*!
* swap-bits.c
* Interchange bits of a byte in the following pattern:
* bit7 <-> bit0
* bit6 <-> bit1
* bit5 <-> bit2
* bit4 <-> bit3
*
*/
#include <stdio.h>
#include <stdlib.h>

#define mask(byte, pos) ((byte) & ~(1<<(pos)))
#define get_bit(byte, pos) ((byte) & (1<<(pos)))
#define program_bit(byte, pos, low_high)    \
        byte = mask(byte, pos);             \
        if (low_high)                       \
            byte  = byte | (1<<pos);

int
main (void)
{
    unsigned char byte = 0×0;
    int i, j;
    int bit_i, bit_j;

    printf("byte: %x\n", byte);
    for(i=0, j=7; i<j; i++, j–)
    {
        bit_i = get_bit(byte, i);
        bit_j = get_bit(byte, j);
        program_bit(byte, i, bit_j);
        program_bit(byte, j, bit_i);
    }
    printf("byte: %x\n", byte);

    return EXIT_SUCCESS;
}

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Related Blog Items

• Bit swapping - Style I
• Swapping nodes in a single linked list
• What do I need to know when mixing C and C++ code?
• Swapping variables without additional space
• Sorting A Linked List with Bubble Sort

This entry was written by Vijay Zanvar and posted on February 6, 2007 at 4:07 pm and filed under Algorithms, Bits & Bytes Manipulation. Bookmark the permalink. Follow any comments here with the RSS feed for this post. Post a comment or leave a trackback: Trackback URL.