logical.pdf

# logical.pdf - COMP-273 Logical and Shift Operations Kaleem...

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Slides From Patterson’s 61C 1 COMP-273 COMP-273 Logical and Shift Operations Kaleem Siddiqi

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Slides From Patterson’s 61C 2 COMP-273 Overview ° Logical Instructions ° Shifts
Slides From Patterson’s 61C 3 COMP-273 Bitwise Operations (1/2) ° Up until now, we’ve done arithmetic ( add , sub,addi ), memory access ( lw and sw ), and branches and jumps. ° All of these instructions view contents of register as a single quantity (such as a signed or unsigned integer) ° New Perspective : View contents of register as 32 bits rather than as a single 32-bit number

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Slides From Patterson’s 61C 4 COMP-273 Bitwise Operations (2/2) ° Since registers are composed of 32 bits, we may want to access individual bits (or groups of bits) rather than the whole. ° Introduce two new classes of instructions: Logical Operators Shift Instructions (we’ve seen sll already)
Slides From Patterson’s 61C 5 COMP-273 Logical Operators (1/4) ° Two basic logical operators: AND: outputs 1 only if both inputs are 1 OR: outputs 1 if at least one input is 1 ° In general, can define them to accept >2 inputs, but in the case of MIPS assembly, both of these accept exactly 2 inputs and produce 1 output Again, rigid syntax, simpler hardware

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Slides From Patterson’s 61C 6 COMP-273 Logical Operators (2/4) ° Truth Table: standard table listing all possible combinations of inputs and resultant output for each ° Truth Table for AND and OR A B AND OR 0 0 0 1 1 0 1 1 0 1 1 1 0 0 0 1
Slides From Patterson’s 61C 7 COMP-273 Logical Operators (3/4) ° Logical Instruction Syntax: 1 2,3,4 where

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• Spring '09
• Vybihal

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