Slide 12.5: Decision directives (cont.)

Decision Directives (Cont.)

The .IF directive is expanded into assembly language instructions including the CMP. Assume val1 and result 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
.data opnd1 BYTE 1 opnd2 BYTE 2 .code .IF ( opnd1 < opnd2 ) call WaitMsg .ENDIF	.data opnd BYTE -1 .code .IF ( opnd < 0 ) call WaitMsg .ENDIF	.data opnd SBYTE -1 .code .IF ( opnd < 0 ) call WaitMsg .ENDIF
Output	Output	Output

Memory & Register	Register Comparison	Constant Comparison
.data opnd SBYTE -1 .code mov al, 0 .IF ( opnd < al ) call WaitMsg .ENDIF	.code mov eax, -4 .IF ( eax < 0 ) call WaitMsg .ENDIF	.code mov eax, -4 .IF ( 0 > eax ) call WaitMsg .ENDIF
Output	Output	Output