IF OPERATOR: INTEL EXAMPLES

Here you can see the results of full conditional operators translation. You may need to look for some details about conditions coding and how assign operator is compiling.

1. IF x<0 THEN s := -1 ELSE s := 1; (4FE - address of variable x, 4FC - s)

Address, code	Operations	Pascal comments
286 A1 FE 04	mov ax,[04FE]	Extract x
289 B9 00 00 28C 39 C8	mov cx,0 cmp ax,cx	Is x < 0 ?
28E 7D 08	jge 298 (if >=0)	Jump to ELSE branch
290 B8 FF FF 293 A3 FC 04	mov ax,ffff (i.e. -1) mov [04FC],ax	THEN s := -1;
296 EB 06	jmp 29E	ELSE bypass
298 B8 01 00 29B A3 FC 04	mov ax,1 mov [04FC],ax	ELSE s := 1;
29E

2. IF x<0 THEN s := -1; (4FE - address of variable x, 4FC - s)
This short form of IF operator can be easily derived from the previous example by removal of ELSE branch and its bypass:

Address, code	Operations	Pascal comments
286 A1 FE 04	mov ax,[04FE]	Extract x
289 B9 00 00 28C 39 C8	mov cx,0 cmp ax,cx	Is x < 0 ?
28E 7D 06	jge 296 (if >=0)	Jump to next operator
290 B8 FF FF 293 A3 FC 04	mov ax,ffff (i.e. -1) mov [04FC],ax	THEN s := -1;
296

3. IF b THEN c := '0' ELSE c := '1'; (4FD - address of BOOLEAN variable b, 4FC - c)

Address, code	Operations	Pascal comments
299 A0 FD 04 29C 30 E4	mov al,[04FD] xor ah,ah (clear ah)	Extract b (byte value)
29E B9 00 00 2A1 39 C8	mov cx,0 cmp ax,cx	Is b <> 0 (TRUE)?
2A3 74 08	jz 2AD (if =0)	Jump to ELSE branch if FALSE
2A5 B8 30 00 2A8 A2 FC 04	mov ax,30 mov [04FC],ax	THEN c := '0';
2AB EB 06	jmp 2B3	ELSE bypass
2AD B8 31 00 2B0 A2 FC 04	mov ax,31 mov [04FC],al	ELSE c := '1';
2B3