Efficient Algorithm for Bit Reversal (from MSB->LSB to LSB->MSB) in C

Question

What is the most efficient algorithm to achieve the following:

0010 0000 => 0000 0100

The conversion is from MSB->LSB to LSB->MSB. All bits

Answer 1

You might want to use the standard template library. It might be slower than the above mentioned code. However, it seems to me clearer and easier to understand.

 #include
 #include


 template
 const std::bitset reverse(const std::bitset& ordered)
 {
      std::bitset reversed;
      for(size_t i = 0, j = N - 1; i < N; ++i, --j)
           reversed[j] = ordered[i];
      return reversed;
 };


 // test the function
 int main()
 {
      unsigned long num; 
      const size_t N = sizeof(num)*8;

      std::cin >> num;
      std::cout << std::showbase << std::hex;
      std::cout << "ordered  = " << num << std::endl;
      std::cout << "reversed = " << reverse(num).to_ulong()  << std::endl;
      std::cout << "double_reversed = " << reverse(reverse(num)).to_ulong() << std::endl;  
 }