Slide 7.6: Flags affected by addition and subtraction (cont.)

Flags Affected by Addition and Subtraction (Cont.)

`0FFh + 1`	`00h – 1`	`00h – 1`
.data X SWORD 12FFh .code movsx ebx, X inc bl call DumpRegs jz L1 call WaitMsg L1: mov X, bx movsx eax, X call WriteHex	.data X SWORD 0FF00h .code movsx ebx, X dec bl call DumpRegs mov X, bx js L1 call WaitMsg L1: movsx eax, X call WriteHex	.data X SWORD 0FF00h .code movsx ebx, X sub bl, 1 call DumpRegs mov X, bx js L1 call WaitMsg L1: movsx eax, X call WriteHex
Output	Output	Output
CF= SF= ZF= OF= AF= PF= EAX=	CF= SF= ZF= OF= AF= PF= EAX =	CF= SF= ZF= OF= AF= PF= EAX=

The INC and DEC instructions do not affect the Carry flag.
The ADD instruction performs the addition based on the size of the first argument. The procedure WaitMsg, provided by the textbook author, displays the message “Press [Enter] to continue ....,” and waits for the user to press the Enter key.

`[X + 1] + 1`	`0FF0Fh + 1`	`0101h + 1`
.data X SWORD 0FF00h .code add X+1, 1 call DumpRegs jz L1 call WaitMsg L1: movsx eax, X call WriteHex	.code mov bx, 0FF0Fh add bl, 1 call DumpRegs lahf test ah, 00010000b jz L1 call WaitMsg L1: movsx eax, bx call WriteHex	.code mov bx, 0101h add bx, 1 call DumpRegs jp L1 call WaitMsg L1: movsx eax, bx call WriteHex
Output	Output	Output
CF= SF= ZF= OF= AF= PF= EAX=	CF= SF= ZF= OF= AF= PF= EAX=	CF= SF= ZF= OF= AF= PF= EAX=