Slide 12.5: Decision directives (cont.)

Decision Directives (Cont.)

The directive is expanded into assembly language instructions including the . Assume and are 32-bit unsigned integers:

mov eax, 6 .IF ( eax > val1 ) mov result, 1 .ENDIF

⇒

mov eax, 6 cmp eax, val1 jbe @C0001 ; unsigned comparison mov result, 1 @C0001: ; created by assembler

If the comparison involves an unsigned variable, an unsigned conditional jump instruction will be inserted in the generated code.

If the comparison involves a signed variable, a signed conditional jump instruction will be inserted in the generated code.

If registers are compared, an unsigned conditional jump instruction will be inserted in the generated code.

Memory Comparison	Unsigned Comparison	Signed Comparison
INCLUDE Irvine32.inc .data opnd1 BYTE 1 opnd2 BYTE 2 .code main PROC .IF ( opnd1 < opnd2 ) call WaitMsg .ENDIF exit main ENDP END main	INCLUDE Irvine32.inc .data opnd BYTE -1 .code main PROC .IF ( opnd < 0 ) call WaitMsg .ENDIF exit main ENDP END main	INCLUDE Irvine32.inc .data opnd SBYTE -1 .code main PROC .IF ( opnd < 0 ) call WaitMsg .ENDIF exit main ENDP END main
Output	Output	Output

Memory & Register	Register Comparison	Constant Comparison
INCLUDE Irvine32.inc .data opnd SBYTE -1 .code main PROC mov al, 0 .IF ( opnd < al ) call WaitMsg .ENDIF exit main ENDP END main	INCLUDE Irvine32.inc .data dummy WORD ? .code main PROC mov eax, -4 .IF ( eax < 0 ) call WaitMsg .ENDIF exit main ENDP END main	INCLUDE Irvine32.inc .data dummy WORD ? .code main PROC mov eax, -4 .IF ( 0 > eax ) call WaitMsg .ENDIF exit main ENDP END main
Output	Output	Output

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