1. - M.Senthil Kumar, AP/CSE
CS6303 – COMPUTER
ARCHITECTURE
(Regulation 2013)
UNIT II – Arithmetic
Operations

2. Unit – II Syllabus
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5.1. ALU
5.2. Addition and subtraction (BB)
5.3. Multiplication
5.4. Division
5.5. Floating Point operations
5.6. Sub word parallelism

3. 5.1. ALU Design
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4. An Arithmetic Logic Unit (ALU) is a digital
electronic circuit that performs arithmetic
and bitwise logical operations on integer
binary numbers.
It is a fundamental building block of the
CPU in all computers.
The inputs to an ALU are the data to be
operated on and a code indicating the
operation to be performed.
ALU – How it works in computer?
5.1. ALU (Contd..)
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5. 5.3. Multiplication
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Normal Multiplication is done as:
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6. 5.3.Multiplication (H/W)
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7. 5.3.Multiplication (H/W)
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8. 5.3. Multiplication (Booth’s)
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Booths Multiplication Recoding table:
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9. 5.3. Multiplication (Booth’s)
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10. 5.4. Division
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11. 5.4. Division
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12. 5.4. Division (Restoring Algm)
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13. 5.4. Division (Restoring Algm)
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14. 5.4 Division (Non-Restoring Algm)
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15. 5.5. Floating point Operations
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16. 5.5. Floating point Operations
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 Going beyond signed and unsigned integers, programming
languages support numbers with fractions, which are called
real's in mathematics.
 Eg:0.000000001ten or 1.0ten x10-9
 Notice that in the last case, the number didn’t represent a
small fraction, but it was bigger than we could represent
with a 32-bit signed integer.
 The alternative notation for the last two numbers is called
scientific notation, which has a single digit to the left of
the decimal point. A number in scientific notation that has no
leading 0s is called a normalized number, which is the
usual way to write it. For example, 1.0ten × 10-9 is in
normalized scientific notation, but 0.1ten × 10-8 and 10.0ten
× 10 -10 are not.

17. 5.5. Floating point Operations
(Contd..) A designer of a floating-point representation must find
a compromise between the size of the fraction and
the size of the exponent, because a fixed word
size means you must take a bit from one to add a bit
to the other.
 This tradeoff is between precision and range:
increasing the size of the fraction enhances the
precision of the fraction, while increasing the size of
the exponent increases the range of numbers that
can be represented.
 Floating-point numbers are usually a multiple of the
size of a word.
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18. 5.5. Floating point Operations
(Contd..)
 F involves the value in the fraction field;
 E involves the value in the exponent field;
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19. 5.5. Floating point Operations
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20. 5.6. Sub Word Parallelism
 It's another name for SIMD-Within-A-Register (SWAR), or register-
sized vector operations.
 The idea is that if you have registers which can hold machine words
of multiple times of your data type size, you can pack several data
elements into them, and make single instructions affect all of those
simultaneously.
 A 128-bit register, for instance, can hold two 64-bit floating point
values; as long as your 'multiply' instruction is aware that the register
is split in the middle, you can get 2 multiplications out of 1
operation.
 A sub word is a lower precision unit of data contained within a word.
 In sub word parallelism, we pack multiple subwords into a word and
then process whole words.
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21. 5.6. Sub Word Parallelism (Contd..)
 It is possible to apply subword parallelism to
noncontiguous subwords of different sizes
within a word.
 however, implementations are much simpler if
we allow only a few subword sizes and if a
single instruction operates on contiguous
subwords that are all the same size.
 One key advantage of subword parallelism is
that it allows general-purpose processors to
exploit wider word sizes even when not
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