Day 6/30 : Bit Manipulation Techniques In C

1. Core Bitwise Operators

• AND (): Sets bits to 1 only if both bits are 1.

• OR (): Sets bits to 1 if either bit is 1.

• XOR (): Sets bits to 1 if bits differ.

• NOT (): Flips all bits (unary operator).

• Left Shift (): Shifts bits left, padding with 0s.

• Right Shift (): Shifts bits right (padding depends on sign).

2. Essential Techniques

• Set a Bit:

• num |= (1 << n); // Set nth bit

• Clear a Bit:

• num &= ~(1 << n); // Clear nth bit

• Toggle a Bit:

• num ^= (1 << n); // Toggle nth bit

• Check a Bit:

• if (num & (1 << n)) // Check if nth bit is set

• Modify Multiple Bits:

• num = (num & ~0x0F) | 0xA; // Set lower 4 bits to 1010

3. Advanced Operations

• Swap Values (without temp):

• a ^= b;

• b ^= a;

• a ^= b;

• Check Even/Odd:

• if (num & 1) // Odd if true

• Count Set Bits:

• int count = 0;

• while (num) {

• num &= (num - 1); // Clear the least significant set bit

• count++;

• }

• Isolate Rightmost 1:

• rightmost = num & -num;

4. Bitmasks & Shifts

• Extract Bits:

• unsigned extract = (num >> offset) & mask;

• Rotate Bits (left by ):

• result = (num << n) | (num >> (sizeof(num)*8 - n));

5. Best Practices

• Use types to avoid sign-extension issues.

• Avoid undefined behavior: Don’t shift by bit width (e.g., for ).

• Use parentheses for clarity: ≠ .

• Preprocessor helpers:

• #define BIT_SET(num, n) ((num) |= (1U << (n)))

• #define BIT_CLEAR(num, n) ((num) &= ~(1U << (n)))

Example: Bitwise Functions

Key Takeaways:

• Bit manipulation enables efficient low-level control.

• Crucial for embedded systems, cryptography, and performance-critical code.

• Always document bitwise operations for readability.