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csc205 Notes 2011 01 11

Posted in csc205 by bnmng on 2011 01/11

Classes start at 5PM

Reading Assignment
Chapter 3 to page 112
3.1 unsigned integers, binary storage, integers, base conversion, range, additions carry bix

Notes:
Machines do not store numbers, they store symbols. We can interpret 10110110 as many different things.

Range of unsigned numbers:
2 bits 4 bits
x x x x x x
0 0 = 0 0 0 0 0 = 0
1 1 = 3 1 1 1 1 = 15
range of n bits is to 2^n – 1
numbers in n bits range is 2^n

Truth Table
Carry In x y sum Carry Out
0 0 0 0 0
0 0 1 1 0
0 1 0 1 0
0 1 1 0 0
The above acts like an xor

1 0 0 1 0
1 0 1 0 1
1 1 0 0 1
1 1 1 1 1
The above acts like an or

When you think about addition, think about the sum and the carry.

101001
000100
——— No carries, no error
101101

1 carry
101101
000110 carry in of i + 1 is carry out if i. Assume the carry in of the lsd is zero.
——–
101011

100111
110100
——– Error Condition Carry out of msb
Carry goes to the carry flag.

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