Computer Science 237
Computer Organization

Lecture 03: Binary Arithmetic, Signed Representations
Date: September 13, 2006

Announcements
- Not CS, but potentially interesting talk tonight: Shuttle astronaut Stephanie Wilson, Brooks-Rogers, 7 PM.
- My office hours on Friday may start and end early. Come by if you need help!
Lab continues - ask questions when stuck
- Thrown into the deep end and don't know how to swim?
- You will soon know what I'm talking about on pages 1 and 2. If not today, then Friday, I promise.
- Suggestion: avoid the sqrt function, in fact avoid the math library altogether
- Useful C functions: atoi(3), scanf(3).
- Useful C ideas: bit shifts and logical operators.
- Useful C example: show_bytes from last time.
- TA hours Sunday evening in TCL 312. I hope to be around some then, too.
Memory model and pointers
- Know your prefixes: Kilo, Mega, Giga, Tera, Peta, Exa, Zetta, Yotta
- Just think of memory as a big array of bytes.
- A pointer? Just a memory location whose contents is a memory location.
Strings and arrays
- no Strings in C - just use an array of char.
Math
- unsigned addition and multiplication
- signed integer representations
  - signed magnitude
  - Excess N
  - 1's complement
  - 2's complement
- signed addition