# CS代写 Binary Representations Integers – cscodehelp代写

Binary Representations Integers

• High-level language program (in C) swap (int v[], int k) {
int temp = v[k]; v[k] = v[k+1]; v[k+1] = temp;
• Assembly language program (for MIPS) swap: sll \$2, \$5, 2 add \$2, \$4,\$2
C compiler
The Big Picture
}
lw \$15, lw \$16, sw \$16, sw \$15, jr \$31
0(\$2)
4(\$2)
0(\$2)
4(\$2) assembler vets
• Machine (object) code (for MIPS)
000000 00000 00101 0001000010000000 000000 00100 00010 0001000000100000

Agenda • Bits, Bytes, and Words
• Numberbasesandbaseconversion – Unsigned Integers
– Signed Integers
• Binaryarithmetic

How do people and computers represent numbers?

Why Base 10? Why Base 2?
• Decimal: Base 10, a single number from 0-9
• Binary: Base 2, a single digit is called a bit (binary digit)
• A bit is the smallest unit of information, and can represent… –1/0
– True / False
– Yes / No
– On/Off
– used in a two-state (Boolean) logic
• Can represent anything with a sequence of binary bits, but the bit patterns have no intrinsic meaning by themselves!

Nibbles to Words
• A bit is the smallest unit
• Typically store information in groups
– a byte is a group of 8 bits Mega bit = 1024 kilo bits • e.g. 01100101 Giga bit = 1024 mega bits
– a nibble/nybble (a small bite) is a group of 4 bits, • e.g. 0110
– a word is a group of 4 bytes, or 32 bits
• e.g. 01100101011001010110010101100101 • We will see it in MIPS
• Least significant bit at the right most

How to Represent Unsigned Integers?

Numbers and Positional Notation • A number with n digits in base b: an-1 … a1 a0
• Therealvalue:N=an-1 bn-1 +…+a1b1 +a0b0 Ais an3922
• 23810 NE Aix o taixiotAox10
Ao o ai I Azzo
• 110102

What is the largest unsigned integer with n digits? • What is the largest decimal number with n digits?
10n – 1
• What is the largest unsigned integer in base 2 with n digits?
2n – 1
• What is the largest unsigned integer in base b with n digits? bn – 1

How many bits are needed to represent an unsigned integer?
• How many digits are needed for numbers up to one million?
• Decimal:
1000001 E lo
• Binary:
2
n 1000000 N
oooooo e lo I n log 1000001
I 1000000
1000000 can I 1000001 20
6.00000436
27

Common Bases
Name of Base
Base
Digits used
Decimal
10
0,1,2,3,4,5,6,7,8,9
Binary
2
0,1
Octal
8
0,1,2,3,4,5,6,7
16
0,1,2,3,4,5,6,7,8,9,A,B,C,D,E,F
• We often write hex numbers preceded by 0x 10112 = 1110 = B16 = 0xB
10112 11102 By a 0 116

How to Convert from one Base to Another?

Base Conversion – Decimal to Another Base
• Approach1:Makeatable
– Divide by bi
– The quotient is the most significant bit – Repeat with the remainder
• Approach2:
– Divide by b
– Remainder of result is least significant bit – Repeat with the quotient

Base Conversion – Decimal to Another Base
• Example: What is 52310 in binary?
EEE
I o
32 I
78 BEATE
i
2
245

Base Conversion – Decimal to Another Base • Example: What is 5324110 in hexadecimal?
21
53241

Base Conversion – Other Base to Decimal
• BasicApproach:Directexpansionwithpositionalweights N = anbn + an-1bn-1 +……+ a1b + a0

Base Conversion – Other Base to Decimal
• Examples: What is 10101012 in Decimal
• It would be useful to remember what 2i is

Base Conversion – Other Base to Decimal • Examples: What is 1AB16 in Decimal?

Base Conversion – Base A to Base B
• Conversion from base a to base b – First convert base a to decimal
– Then convert decimal to base b
• Special cases (easier by grouping) – Binary to hexadecimal and back
• Example: 110101011012
– Binary to octal and back
• Example: 7608 becomes 1111100002

The Hitchhiker’s Guide to the Galaxy What is the question to life, the universe, and everything?

How to Represent Signed Integers?

Signed Integers
• We will show you 3 approaches – Add a sign bit
– One’s Complement
– Two’s Complement
• Yourcomputerisusingtwo’scomplement

Sign-and-Magnitude • The first approach
• Use the most significant bit to represent the sign +13= 0000 1101
-13 = 1000 1101
• Problems
– Two representations for zero: 0000 0000 and 1000 0000
– Cannot add a positive number and a negative number together

• Invert each bit! +13= 0000 1101 -13 = 1111 0010
One’s Complement
• Problems:
– Still two representations for zero 0000 0000 and 1111 1111 – Answer is off by 1
– Incorrect overflow • What is 16 + (-13)?

Two’s Complement
• The gold standard: Invert the bits and add one! • +13 = 0000 1101
• What is –13?
• Easily implemented in hardware
• Uniquezero 0000 0000
• MSB represents the sign. – 1 if negative
– 0 if positive
Decimal
Binary
0
000
1
001
2
010
3
011
-4
100
-3
101
-2
110
-1
111

Two’s Complement • Negative numbers are defined as -Y = Bn – Y
• Range from -2n-1 to 2n-1 – 1
• The complement of complement of Y is Y, -(-Y) = Y.
Decimal
Binary
0
000
1
001
2
010
3
011
-4
100
-3
101
-2
110
-1
111

Binary Arithmetic
Subtraction
Multiplication
0+0=0
0-0=0
0*0=0
0+1=1
0 – 1 = 0 + (-1)
0*1=0
1+0=1
1-0=1
1*0=0
1 + 1 = 0 carry 1
1-1=0
1*1=1
• Rules in base 10 are also valid in any other base