ITEC 122 2008fall ibarland

home—info—lectures—exams—archive

lect11a
implementing ints
two's complement

Fixed-point arith:
- to motivate, compare 5-bit vs 3-decimal-digit
- unsigned range:
- signed range:
Two problems w/ sign: 
 - +/-0; 
 - addition of negatives means doing a separate subtraction algorithm.
   (What happens if we did try 
  examples:  57+-30; 57+-80; 4+-2; 4+-10

Try 2's complement:
  invert every bit; then add 1
  4+-2    4+-10
Why?  Compare to 10's complement:
  57+-30; 57+-80
  Hey, 10's complement of (-n) is 1000-n.
   57+(1000-30); 57+(1000-80)

home—info—lectures—exams—archive

©2008, Ian Barland, Radford University Last modified 2008.Dec.08 (Mon)

Please mail any suggestions (incl. typos, broken links) to iba�rlandrad�ford.edu