[RESOLVED] how is bit shifting used in bitarray class

[shansari]

I can not get my head around what is happening in the lines below with the << operator. I have put a comment under each line. This code is from BitArray class, and Jeff Richter uses it in his book C# via CLR. It is on page 244.

public sealed class BitArray {
  private Byte[] m_byteArray;
  private Int32 m_numBits;
//constructor that allocates the byte array and sets all bits to zero
public BitArray (Int32 numBits) {
// validate arguments first
if (numBits <= 0)
   throw new ArgumentOutOfRangeException("numBits must be > 0");
// Save the number of bits. 
m_numBits = numBits;
// Allocate the bytes for the bit array.
m_byteArray = new Byte[(numBits + 7) / 8];
}
// This is the indexer (parameterful property).
public Boolean this[Int32 bitPos] {

// This is the indexer's get accessor method
  get {
    // Validate arguments first
    if ((bitPos < 0) || (bitPos >= m_numBits))
       throw new ArgumentOutOfRangeException("bitPos");
    // Return the state of the indexed bit
    return (m_byteArray[bitPos / 8] & ( 1 << (bitPos % 8  ))) != 0;
//What is happening in the above code? Why are we shifting 1s mod number of bitPos?
}
//This is the indexer's set accessor method.
set {
  if ((bitPos < 0) || (bitPos >= m_numBits))
      throw new ArgumentOutOfRangeException("bitPos", bitPos.ToString());
  if (value) {
     // Turn the indexed bit on.
     m_byteArray[bitPos / 8] = (Byte)
        (m_byteArray[bitPos /8] | (1 << (bitPos % 8)));
  } else {
     // Turn the indexed bit off.
     m_byteArray[bitPos /8] = (Byte)
        (m_byteArray[bitPos / 8] & ~(1 << (bitPos % 8)));
//In the above code the opposite is happening; there is a "~" next to the shif expression
  }
 }
}
}

[shansari]

I figured out what is going on. Bitarray indexer performs an and operation with what is the bitPos and 1.