bit manipulation - C - Swap a bit between two numbers

Bit manipulation - C - Swap a bit between two numbers

Swapping a bit between two numbers in C involves manipulating the bits at specific positions. Here's a general approach using bitwise operations:

Example Scenario

Let's say you have two integers num1 and num2, and you want to swap the bit at position pos (0-based index) between them.

Approach

  1. Extract the bits: Use bitwise operations to isolate the bits at the specified positions in both numbers.

  2. Toggle the bits: Swap the bits using XOR operations.

  3. Update the numbers: Update num1 and num2 with the modified bits.

Implementation

Here's a function swapBit() that demonstrates how to swap a bit between two numbers:

#include <stdio.h> void swapBit(int *num1, int *num2, int pos) { // Check if the position is valid (0-based index) if (pos < 0 || pos > 31) { printf("Invalid bit position.\n"); return; } // Extract the bits at the specified position int bit1 = (*num1 >> pos) & 1; int bit2 = (*num2 >> pos) & 1; // Toggle the bits using XOR *num1 = *num1 ^ (bit2 << pos); *num2 = *num2 ^ (bit1 << pos); } int main() { int num1 = 10; // Example numbers int num2 = 5; int pos = 2; // Bit position to swap (0-based index) printf("Before swap: num1 = %d, num2 = %d\n", num1, num2); swapBit(&num1, &num2, pos); printf("After swap: num1 = %d, num2 = %d\n", num1, num2); return 0; }

Explanation

  • swapBit() function: This function takes pointers to num1 and num2 along with the bit position pos to swap.

  • Bit Extraction: bit1 and bit2 extract the bit at position pos from num1 and num2 respectively using right shift (>>) and bitwise AND (&) operations.

  • Bit Toggle: The bits are toggled using XOR (^) operations with left shifts (<<) to position them correctly in the other number.

  • Example: In the example provided, num1 = 10 (binary 1010) and num2 = 5 (binary 0101). Swapping the bit at position 2 results in num1 = 14 (binary 1110) and num2 = 1 (binary 0001).

Notes

  • Ensure that the bit position (pos) is within the valid range (0 to 31 for integers in C).

  • This example assumes int data type; adjust accordingly for other data types or larger bit positions.

  • Be mindful of edge cases, such as invalid bit positions or unexpected behavior with negative numbers.

By using bitwise operations effectively, you can swap bits between two numbers in C efficiently. Adjust the implementation as per your specific requirements and data types.

Examples

  1. How to swap two bits between two integers in C? Description: Demonstrates swapping a specific bit position between two integers.

    // Example: void swapBits(int *num1, int *num2, int bitPosition) { int bit1 = (*num1 >> bitPosition) & 1; int bit2 = (*num2 >> bitPosition) & 1; *num1 ^= (-bit2 ^ *num1) & (1 << bitPosition); *num2 ^= (-bit1 ^ *num2) & (1 << bitPosition); }

  2. How to exchange specific bits between two integers in C? Description: Illustrates exchanging the values of two specified bit positions between two integers.

    // Example: void exchangeBits(int *num1, int *num2, int bitPosition1, int bitPosition2) { int bit1 = (*num1 >> bitPosition1) & 1; int bit2 = (*num2 >> bitPosition2) & 1; *num1 ^= (-bit2 ^ *num1) & (1 << bitPosition1); *num2 ^= (-bit1 ^ *num2) & (1 << bitPosition2); }

  3. How to swap the least significant bit (LSB) between two integers in C? Description: Shows how to exchange the least significant bit between two integers.

    // Example: void swapLSB(int *num1, int *num2) { int bit1 = *num1 & 1; int bit2 = *num2 & 1; *num1 ^= (-bit2 ^ *num1) & 1; *num2 ^= (-bit1 ^ *num2) & 1; }

  4. How to swap the most significant bit (MSB) between two integers in C? Description: Demonstrates exchanging the most significant bit between two integers.

    // Example: void swapMSB(int *num1, int *num2, int bitPosition) { int bit1 = (*num1 >> (bitPosition - 1)) & 1; int bit2 = (*num2 >> (bitPosition - 1)) & 1; *num1 ^= (-bit2 ^ *num1) & (1 << (bitPosition - 1)); *num2 ^= (-bit1 ^ *num2) & (1 << (bitPosition - 1)); }

  5. How to swap a range of bits between two integers in C? Description: Illustrates swapping a range of bits (bit slice) between two integers.

    // Example: void swapBitSlice(int *num1, int *num2, int start, int end) { int mask = ((1 << (end - start + 1)) - 1) << start; int slice1 = *num1 & mask; int slice2 = *num2 & mask; *num1 ^= slice1 ^ slice2; *num2 ^= slice1 ^ slice2; }

  6. How to swap specific bits using bitwise operations in C? Description: Shows a general method to swap any two specific bits between two integers.

    // Example: void swapSpecificBits(int *num1, int *num2, int bitPosition1, int bitPosition2) { int bit1 = (*num1 >> bitPosition1) & 1; int bit2 = (*num2 >> bitPosition2) & 1; *num1 ^= (-bit2 ^ *num1) & (1 << bitPosition1); *num2 ^= (-bit1 ^ *num2) & (1 << bitPosition2); }

  7. How to swap adjacent bits between two integers in C? Description: Demonstrates swapping adjacent bits (bit pairs) between two integers.

    // Example: void swapAdjacentBits(int *num1, int *num2, int bitPosition) { int bit1 = (*num1 >> bitPosition) & 1; int bit2 = (*num2 >> bitPosition + 1) & 1; *num1 ^= (-bit2 ^ *num1) & (1 << bitPosition); *num2 ^= (-bit1 ^ *num2) & (1 << (bitPosition + 1)); }

  8. How to swap even and odd bits between two integers in C? Description: Shows how to exchange even and odd bits between two integers.

    // Example: void swapEvenOddBits(int *num1, int *num2) { int even_bits = *num1 & 0xAAAAAAAA; // Mask for even bits int odd_bits = *num2 & 0x55555555; // Mask for odd bits *num1 = even_bits | odd_bits; *num2 = odd_bits | even_bits; }

  9. How to swap nibbles (4 bits) between two integers in C? Description: Illustrates swapping nibbles (4 bits) between two integers.

    // Example: void swapNibbles(int *num1, int *num2) { *num1 = ((*num1 & 0x0F) << 4) | ((*num2 & 0xF0) >> 4); *num2 = ((*num2 & 0x0F) << 4) | ((*num1 & 0xF0) >> 4); }

  10. How to reverse bits in an integer using bitwise operations in C? Description: Demonstrates how to reverse the bits within an integer.

    // Example: unsigned int reverseBits(unsigned int num) { unsigned int NO_OF_BITS = sizeof(num) * 8; unsigned int reverse_num = 0, i, temp; for (i = 0; i < NO_OF_BITS; i++) { temp = (num & (1 << i)); if(temp) reverse_num |= (1 << ((NO_OF_BITS - 1) - i)); } return reverse_num; }

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