The document discusses different types of flow control instructions in assembly language including conditional jump instructions, unconditional jump instructions, compare instructions, and looping structures. Conditional jump instructions like JG transfer control based on condition flags. Looping structures include for, while, and repeat loops. High-level language equivalents like if-then, if-then-else, and case statements are also covered.

2. PRODIP GHOSH

3. Flow Control
Instructions

4. Flow Control Instructions
 Program using the different instruction :-
 Conditional and Unconditional Jump Instructions
Compare Instruction
Loop Instruction

5. Conditional Jump
Syntax:
Jxxx destination_label
Where xxx represents the condition
If condition is true, the next instruction to be executed is the one at
destination_label.
If condition is false, the instruction immediately following the jump is
done next.

6. Conditional Jump
The destination_label must precede the jump instruction by no more
than 126 bytes.
To implement a conditional jump, the CPU looks at the FLAG
register (set by last instruction executed by the processor).
JMP instructions themselves do not affect flags.

7. Unconditional Jump
Syntax:
JMP destination_label
Purpose: To Transfer control to another part of the program.
Example:
 MOV AX, 5
 MOV BX, 2
 JMP LABEL_SUB
 ADD AX, BX ;this instruction will never execute
 LABEL_SUB:
 SUB AX, BX

8. Categories of Conditional Jump
Signed Jumps: This is used when a signed interpretation is being
given to result.
Symbol Description Condition for Jumps
JG/JNLE Jump if greater than
Jump if not less than or equal to
ZF = 0 and SF = OF
JGE/JNL Jump if greater than or equal to
Jump if not less than
SF = OF
JL/JNGE Jump if less than
Jump if not greater than or equal to
SF <> OF
JLE/JNG Jump if less than or equal to
Jump if not greater than
ZF = 1 and SF <> OF

9. Categories of Conditional Jump
Unsigned Jumps: This is used for an unsigned interpretation of result
Symbol Description Condition for Jumps
JA/JNBE Jump if above than
Jump if not below than or equal to
ZF = 0 and CF = 0
JAE/JNB Jump if above than or equal to
Jump if not below than
CF = 0
JB/JNAE Jump if below than
Jump if not above than or equal to
CF = 1
JBE/JNA Jump if below than or equal to
Jump if not above than
ZF = 1 and CF = 1

10. Categories of Conditional Jump
Single-Flag Jumps: Which operate on settings of individual flags.

11. Compare Instruction
CMP (compare) instruction performs an implied subtraction of a
source operand from destination operand. Neither operand is
modified.
 CMP destination, source
Compare Instruction maintain three condition:
 Destination < Source
 Destination = Source
 Destination > Source

12. Examples

13. OUTPUT

14. High Level Language Structures
Branching Structure
 IF-THEN
 IF-THEN-ELSE
 CASE

15. IF-THEN

16. IF-THEN-ELSE

17. CASE
A case is a multiway branch structure that tests a register,
variable, or expression for particular values or range of
values. The general form is as follows:
Case Expression
values_1: statements_1
values_2: statements_2
…………..
values_n: statements_n
END_CASE

18. CASE Examples

19. High Level Language Structures
Branching with Compound Conditions
 AND CONDITIONS
 OR CONDITIONS

20. AND CONDITION
 An AND condition is true if and only if condition_1 and
condition_2 are both true.
 If any condition is false, then the whole thing is false.

21. AND CONDITION EXAMPLES

22. OR CONDITION
 If condition_1 OR condition_2 is true then an OR conditions is true.
 If both conditions are false, then the whole thing is false.

23. OR CONDITION EXAMPLES

24. High Level Language Structures
Looping Structures
FOR LOOP
WHILE LOOP
REPEAT LOOP

25. LOOPING STRUCTURES
FOR LOOP
Executed at least once.
 If CX contains 0, the loop instruction decrements CX (CX =
FFFFh)
 To prevent this, use instruction JCXZ before the loop.
;initialize CX
JCXZ SKIP
TOP:
;body of the loop
LOOP TOP
SKIP:

26. Examples For Looping Structures

27. LOOPING STRUCTURES
WHILE LOOP
 WHILE condition DO
 ;statements
 END_WHILE
 WHILE LOOP checks the terminating condition at the top of the
loop, so don’t forget to initialize variables.

28. EXAMPLES WHILE STRUCTURES

29. LOOPING STRUCTURES
REPEAT LOOP
 REPEAT
 ;statements
 UNTIL condition
First statements are executed, then the condition is checked.
If true, the loop terminates; if false, control branches to the top of the
loop

30. Examples Repeat Structures