Bit Hacks from Beginner to Advanced - 11 Amazing Bit Twiddling Techniques

Introduction

This tutorial covers 11 bit manipulation techniques ranging from beginner to advanced, as demonstrated in the video "Bit Hacks from Beginner to Advanced - 11 Amazing Bit Twiddling Techniques." These techniques are essential for programmers looking to optimize their code, improve performance, or delve deeper into low-level programming. The hacks include setting, clearing, toggling bits, and more. Let's dive in!

Step 1: Set a Bit

To set a specific bit in a variable, use the bitwise OR operation.

• Syntax:

  number |= (1 << position);
  

• Description: This shifts the number 1 to the left by 'position' and performs a bitwise OR with 'number', ensuring that the bit at that position is set to 1.

Step 2: Clear a Bit

To clear (set to 0) a specific bit, use the bitwise AND operation with a negated bit mask.

• Syntax:

  number &= ~(1 << position);
  

• Description: This shifts the number 1 left by 'position', negates it, and performs a bitwise AND with 'number', effectively clearing the target bit.

Step 3: Toggle a Bit

To toggle the value of a specific bit, use the bitwise XOR operation.

• Syntax:

  number ^= (1 << position);
  

• Description: This shifts the number 1 to the left by 'position' and applies a bitwise XOR with 'number', flipping the bit at that position.

Step 4: Convert Trailing Zeros to Ones

To convert all trailing zeros of a number to ones, use the following technique.

• Syntax:

  number = number | (number + 1);
  

• Description: This effectively turns all trailing zeros into ones.

Step 5: Extract the Least Significant 1 Bit

To extract the least significant 1 bit from a number, use the following operation.

• Syntax:

  least_significant_bit = number & -number;
  

• Description: This utilizes the two's complement to isolate the least significant 1 bit.

Step 6: Masked Copy

To copy bits from one variable to another while masking, follow this approach.

• Syntax:

  target = (source & mask) | (target & ~mask);
  

• Description: This copies only the bits of 'source' defined by 'mask' into 'target'.

Step 7: Swapping Bits

To swap two bits in a number, use the following method.

• Syntax:

  number ^= (1 << pos1) | (1 << pos2);
  

• Description: This toggles the bits at positions 'pos1' and 'pos2'.

Step 8: Population Count

To count the number of set bits (1s) in an integer, use the following algorithm.

• Syntax:

  int count = 0;
  while (number) {
      count += number & 1;
      number >>= 1;
  }
  

• Description: This loops through each bit, counting how many are set.

Step 9: Counting Bit Islands

To count the number of contiguous sequences of 1s (bit islands) in a binary number, utilize this technique.

• Syntax:

  while (number) {
      number &= (number << 1);
      count++;
  }
  

• Description: This will continuously clear all bits in a sequence until none remain.

Step 10: Bit Scan Forwards

To find the index of the first set bit (1) in a number, use this method.

• Syntax:

  int index = __builtin_ctz(number);
  

• Description: The __builtin_ctz function counts the number of trailing zeros, giving the index of the first set bit.

Step 11: Next Lexicographic Permutation

To get the next permutation of bits in a number, use this algorithm.

• Syntax:

  unsigned int next = (number & -number) + number;
  number = next + (((number ^ next) / (number & -number)) >> 2);
  

• Description: This calculates the next permutation in a lexicographic order.

Conclusion

This tutorial covered 11 essential bit manipulation techniques that can enhance your programming skills. These techniques are crucial for efficient coding, especially in low-level programming. To practice, try implementing each method in your own projects and explore their applications in algorithms and data structures. Happy coding!