1. In the following code, the value in AL is intended to be a signed byte Explai
ID: 3754105 • Letter: 1
Question
1. In the following code, the value in AL is intended to be a signed byte Explain how the Overflow flag helps, or does not help you, to determine whether the final value in AL falls within a valid signed range. mov al,-1 add al, 130 2. Trace the following program: 1: main PROC 2: mov eax,5 3: add eax,6 4: sub eax, 6 5: mov ebx, eax what is the value in eax- and in ebx 3. At which level/s can an assembly language program manipulate input/output? 4. How do you reserve space for the stack in a program? 5. How is a source file different from a listing file?Explanation / Answer
Answer:
1)
Overflow flag(OF) works on signed numbers.
When result of addition or subtraction is in range -128 to 127 then OF = 0 else OF = 1.
mov al , -1
add al , 130
These instructions results in al = 129 which is big enough to fit in 8-bit for signed numbers ,hence overflow flag is set to 1.
In other words, 129 is greater than 127 hence is out of range to fit in 8-bits for signed numbers.
If overflow flag is set to 1 then fina value of AL doesnot falls within a valid signed range. If OF =0 then it falls within the range.
3)
The following level/s can an assembly language program manipulate input/output
4)
Reserve space for the stack in a program By subtracting a value from the stack pointer register.
(or)
You can reserve space for a stack in a program using the .STACK directive whichtells the assembler how many bytes of memory to reserve for the program’s runtimestack.
5)
A listing file is used to display the error or errors that the assembler encounters while asource file contains the code representing the various machine instructions (Corporation,1996)
A source file is given as input to the assembler. A listing file has additional text that will not
assemble. It is a file that is created by the assembler.
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