Chap7-arith - Overview ° C operators operands ° Variables...

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Unformatted text preview: Overview ° C operators, operands ° Variables in Assembly: Registers ° Comments in Assembly ° Data Processing Instructions ° Addition and Subtraction in Assembly Review C Operators/Operands (#1/2) ° Operators: + , - , * , / , % (mod); • 7/4==1 , 7%4==3 ° Operands: • Variables: lower , upper , fahr , celsius • Constants: , 1000 , -17 , 15.4 ° Assignment Statement: Variable = expression • Examples: celsius = 5*(fahr-32)/9; a = b+c+d-e; C Operators/Operands (#2/2) ° In C (and most High Level Languages) variables declared frst and given a type • Example: int fahr, celsius; char a, b, c, d, e; ° Each variable can ONLY represent a value oF the type it was declared as (cannot mix and match int and char variables). Assembly Design: Key Concepts ° Keep it simple! • Limit what can be a variable and what can ʼ t • Limit types oF operations that can be done to absolute minimum- iF an operation can be decomposed into a simpler operation, don ʼ t include it.- ¡or example 7%4 operation is complex. We break it into simpler operations in Assembly Assembly Variables: Registers (#1/4) ° Unlike HLL, assembly cannot use variables • Why not? Keep Hardware Simple ° Assembly Operands are registers • limited number of special locations built directly into the hardware • operations can only be performed on these! ° BeneFt: Since registers are directly in hardware, they are very fast Assembly Variables: Registers (#2/4) ° Drawback: Since registers are in hardware, there are a predetermined number of them • Solution: ARM code must be very carefully put together to efFciently use registers ° 16 registers in ARM • Why 16? Smaller is faster ° Each ARM register is 32 bits wide • Groups of 32 bits called a word in ARM Assembly Variables: Registers (#3/4)...
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This note was uploaded on 12/20/2010 for the course CSC CSCC85 taught by Professor Lorincz during the Spring '10 term at University of Toronto.

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Chap7-arith - Overview ° C operators operands ° Variables...

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