Newbie -- bitwise shifts

[Josiah Carlson]

gbblob wrote:

> Can someone please explain to me why left shits are equivalent to
> multiplication and right shifts equivalent to devision?  This seems
> backwards to me.
> 
> e.g.
> 
> 15 is binary 1111
> if I shift this left 2 bits I get 11
> 
> however in Python 15<<2 = 60 ?!

In computer science, shifting a number 'k' bits to the left, is the same 
as adding 'k' zeroes to the right side.  Shifting a number 'j' bits to 
the right, is the same as removing 'j' digits from the right side.

15<<2 == 15 *  2**2
15>>2 == 15 // 2**2

This has been the way of things since at least the 1950's.

  - Josiah