1. EECE.2160 ECE Application Programming
Instructor:
Dr. Michael Geiger
Fall 2018
Lecture 36:
Bitwise operators (continued)

2. ECE Application Programming: Lecture 36
Lecture outline
Announcements/reminders
Office hours Tuesday 12-1:30, not Thursday this week
Today: Program 6 regrades due
Th 12/13: last day of classes; Program 8 due
P8 deals with file I/O (lectures 32-33)
M 12/17: Exam 3, 3-6 PM, Ball 210
Course evals online; will also have hard copies available
You’ll submit eval at exam
W 12/19: All code due by 12:00 PM (noon)
Program 9: Worth up to 4 points extra credit on final avg
Resubmission deadline for P7 & P8
Today’s class
Bitwise operators
9/24/2019
ECE Application Programming: Lecture 36

3. Review: binary and hexadecimal
All data encoded in binary (base 2)
Useful knowing bit patterns to evaluate bitwise ops
Hexadecimal (base 16) used with bitwise ops
Closer to binary than base 10 is
Each hexadecimal digit = 4 bits
Leading 0x indicates hexadecimal constant
Digits 0-9 same as decimal, = A-F
0x0 = 00002, 0x1 = … 0x9 = 10012
0xA = 10102, 0xB = … 0xF = 11112
Variables typically declared as unsigned int
Strictly non-negative whole numbers
32 bits in length
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ECE Application Programming: Lecture 36

4. Review: Bitwise Logical Operations
Deal with individual bits of a value
Each bit is evaluated separately
There is no "Carry" as with addition…i.e. the results of an operation in one bit position has no effect on an adjacent bit.
Operators
&  AND
|  OR
^  XOR
~  bitwise NOT (flip all bits)
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ECE Application Programming: Lecture 36

5. Bitwise Logical Operations
AND A B
A&B 1
NOT A
~ A 1 OR
XOR (exclusive or) A B
A|B 1 A B
A^B 1
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ECE Application Programming: Lecture 36

6. Bitwise Logical Operations
& = ? A B
A&B 1
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ECE Application Programming: Lecture 36

7. Bitwise Logical Operations
& = ? A B
A&B 1
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ECE Application Programming: Lecture 36

8. Bitwise Logical Operations
& = ? A B
A&B 1
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ECE Application Programming: Lecture 36

9. Bitwise Logical Operations
| = ? A B
A | B 1
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ECE Application Programming: Lecture 36

10. Bitwise Logical Operations
ECE 160
02/02/2005
Bitwise Logical Operations
| = ? A B
A | B 1
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ECE Application Programming: Lecture 36
(c) 2005, P. H. Viall

11. Bitwise Logical Operations
| = ? A B
A | B 1
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ECE Application Programming: Lecture 36

12. Bitwise Logical Operations
^ = ? A B
A ^ B 1
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ECE Application Programming: Lecture 36

13. Bitwise Logical Operations
^ = ? A B
A ^ B 1
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ECE Application Programming: Lecture 36

14. Bitwise Logical Operations
^ = ? A B
A ^ B 1
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ECE Application Programming: Lecture 36

15. Bitwise Logical Operations
ABCD | FF00 &
FFCD
NOTE: & is a higher precedence than | similar to * being a higher precedence than + in algebra. A B
A&B
A|B
A^B 1
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ECE Application Programming: Lecture 36

16. ECE Application Programming: Lecture 36
Bit shifts
Bit shift operators
Left shift: <<
Right shift: >>
Shifts in 0s (with unsigned ints)
x << n shifts x left by n bits
Equivalent to x * 2n
e.g. 1 << 5 = ( ) << 5 =
x >> n shifts x right by n bits
Equivalent to x / 2n
e.g. 8 >> 3 = ( ) >> 3 =
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ECE Application Programming: Lecture 36

17. ECE Application Programming: Lecture 36
Review: C operators
Operator
Associativity
Innermost ( )
Left to right
Unary -, unary ~
Right to left
* / %
<< >>
NOTE: shift amt < 32
& ^ |
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ECE Application Programming: Lecture 36

18. Example: Bitwise operations
Evaluate each of the following expressions if you have the following unsigned ints:
A = 7, B = 10, and C = 0xFFFFFFFF
A & B
A | ~B
A ^ C
A << 4
B >> 5
A | (B << 2)
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ECE Application Programming: Lecture 36

19. ECE Application Programming: Lecture 36
Example: Solution
First step: convert A & B to binary (or hex)
A = 7 = = 0x7
B = 10 = = 0xA
Now solve problems
A & B = 0111 & 1010 = 00102
A | ~B = 0111 | ~1010
= 0111 | 0101 = Upper 28 bits = 1!
Final answer: 0xFFFFFFF7
A ^ C = ( ) ^ ( )
= = 0xFFFFFFF8
A << 4 = 0111 << (4 bits) = = 0x70
B >> 5 = 1010 >> (5 bits) = 0
Only lowest 4 bits of B contain non-zero values!
A | (B << 2) = | (1010 << 2 bits)
= 0111 | =
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ECE Application Programming: Lecture 36

20. ECE Application Programming: Lecture 36
Hexadecimal output
To print a number in hex, use %x or %X
%x prints characters a-f in lowercase
%X prints characters A-F in uppercase
To show leading 0x, use the # flag
To show leading 0s, use precision with total # digits
Field width + 0 flag also works unless value = 0
Examples (assume var1 = 0x1A2B)
printf(“%x”, var1)  1a2b
printf(“%X”, var1)  1A2B
printf(“%#x”, var1)  0x1a2b
printf(“%.6x”, var1)  001a2b
printf(“%#.6x”, var1)  0x001a2b
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ECE Application Programming: Lecture 36

21. ECE Application Programming: Lecture 36
Next time
Exam 3 Preview
Reminders:
Office hours Tuesday 12-1:30, not Thursday this week
Today: Program 6 regrades due
Th 12/13: last day of classes; Program 8 due
P8 deals with file I/O (lectures 32-33)
M 12/17: Exam 3, 3-6 PM, Ball 210
Course evals online; will also have hard copies available
You’ll submit eval at exam
W 12/19: All code due by 12:00 PM (noon)
Program 9: Worth up to 4 points extra credit on final avg
Resubmission deadline for P7 & P8
9/24/2019
ECE Application Programming: Lecture 36