Slide 7.7: Flags affected by addition and subtraction (cont.)

Slide 7.6: Flags affected by addition and subtraction (cont.)
Slide 8.1: Multiplication and division instructions
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Flags Affected by Addition and Subtraction (Cont.)

`0FFh + 1`	`80h – 1`	`80h + 0FFh`
INCLUDE Irvine32.inc .data X SBYTE 0FFh .code main PROC add X, 1 call DumpRegs jc L1 call WaitMsg L1: movsx eax, X call WriteHex exit main ENDP END main	INCLUDE Irvine32.inc .data X BYTE 80h .code main PROC sub X, 1 call DumpRegs jc L1 call WaitMsg L1: movsx eax, X call WriteHex exit main ENDP END main	INCLUDE Irvine32.inc .data X BYTE 80h .code main PROC add X, 0FFh call DumpRegs jc L1 call WaitMsg L1: movsx eax, X call WriteHex exit main ENDP END main
Output	Output	Output
CF= SF= ZF= OF= AF= PF= EAX=	CF= SF= ZF= OF= AF= PF= EAX=	CF= SF= ZF= OF= AF= PF= EAX=

Overflow occurs when two positive operands generate a negative sum or two negative operands generate a positive sum.
Overflow never occurs when the signs of two addition operands are different.
The instruction can produce an invalid result if the destination operand can not be stored correctly.
Applying to a nonzero operand always sets the Carry flag.

`128 – 1`	`1 – 2`	`–(–128)`
INCLUDE Irvine32.inc .data X SBYTE -128 .code main PROC sub X, 1 call DumpRegs jc L1 call WaitMsg L1: movsx eax, X call WriteHex exit main ENDP END main	INCLUDE Irvine32.inc .data X SBYTE 1 .code main PROC sub X, 2 call DumpRegs jc L1 call WaitMsg L1: movsx eax, X call WriteHex exit main ENDP END main	INCLUDE Irvine32.inc .data Dummy WORD ? .code main PROC sub eax, eax mov al, -128 neg al call DumpRegs jo L1 call WaitMsg L1: call WriteHex exit main ENDP END main
Output	Output	Output
CF= SF= ZF= OF= AF= PF= EAX=	CF= SF= ZF= OF= AF= PF= EAX=	CF= SF= ZF= OF= AF= PF= EAX=

“I’m not arguing, I’m just explaining why I’m right.”
― Unknown