Jumps in Assembly Language.
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This document discusses jumps in assembly language, including unconditional jumps and conditional jumps. It defines an unconditional jump as a jump without a condition, using the JMP instruction. Conditional jumps use conditions and compare instructions like CMP. Conditional jump instructions include JE/JZ for equal, JNE/JNZ for not equal, JA/JNBE for above, JB/JNAE for below, and others. It also discusses comparing signed vs unsigned numbers and the flags tested for each conditional jump instruction.
![CMP Instruction
Compares the destination operand to the source operand
Nondestructive subtraction of source from destination (destination
operand is not changed)
Syntax:
CMP destination, source
Note:
Cmp reg, reg Cmp dl,aI
Cmp reg, constant Cmp dl, 3
Cmp reg, [memory address] Cmp dl, [sI]
(1 of 3)](https://image.slidesharecdn.com/jumps-191212035951/85/Jumps-in-Assembly-Language-5-320.jpg)
Jumps in Assembly Language.
- 2. JUMP A jump is a instruction used to control the flow of program. Types of jumps: 1. Unconditional Jump 2. Conditional Jump
- 3. Unconditional Jump A jump without using any condition is known as unconditional jump. Or Jump to label without any condition. syntax: JMP label_name Example: Label1: mov dl,'a' mov ah,02 int 21h jmp Label1
- 4. Conditional Jump A jump with using condition is known as conditional jump. Or Jump to label with condition. syntax: J<condition> label_name (Let us discuss the CMP instruction before discussing the conditional instructions.)
- 5. CMP Instruction Compares the destination operand to the source operand Nondestructive subtraction of source from destination (destination operand is not changed) Syntax: CMP destination, source Note: Cmp reg, reg Cmp dl,aI Cmp reg, constant Cmp dl, 3 Cmp reg, [memory address] Cmp dl, [sI] (1 of 3)
- 6. CMP Instruction • Case 3: destination > source mov al,6 mov bl,5 cmp al,bl ; ZF = 0, CF = 0 (2 of 3) mov al,5 mov bl,5 cmp al,bl ; Zero flag set Case 1: destination == source mov al,4 mov bl,5 cmp al,bl ; Carry flag set • Case 2: destination < source The comparisons shown here are performed with “Unsigned" integers.
- 7. CMP Instruction (3 of 3) • Case 1: destination >source mov al,5 Mov bl,-2 cmp al,bl ; Sign flag == Overflow flag • Case 2 : destination < source mov al,-1 Mov bl,5 cmp al,bl ; Sign flag != Overflow flag The comparisons shown here are performed with "signed" integers.
- 8. Conditional Jump For Unsigned Numbers Following are the conditional jump instructions used on unsigned data used for logical operations − Instruction Description Flags tested JE/JZ Jump Equal or Jump Zero ZF JNE/JNZ Jump not Equal or Jump Not Zero ZF JA/JNBE Jump Above or Jump Not Below/Equal CF, ZF JAE/JNB Jump Above/Equal or Jump Not Below CF JB/JNAE Jump Below or Jump Not Above/Equal CF JBE/JNA Jump Below/Equal or Jump Not Above AF, CF
- 9. Conditional Jump For Signed Numbers Following are the conditional jump instructions used on unsigned data used for logical operations − Instruction Description Flags tested JE/JZ Jump Equal or Jump Zero ZF JNE/JNZ Jump not Equal or Jump Not Zero ZF JG/JNLE Jump Greater or Jump Not Less/Equal OF, SF, ZF JGE/JNL Jump Greater/Equal or Jump Not Less OF, SF JL/JNGE Jump Less or Jump Not Greater/Equal OF, SF JLE/JNG Jump Less/Equal or Jump Not Greater OF, SF, ZF
- 10. Conditional Jump With Flags The following conditional jump instructions have special uses and check the value of flags − Instruction Description Flags tested JC Jump If Carry CF JNC Jump If No Carry CF JO Jump If Overflow OF JNO Jump If No Overflow OF JP/JPE Jump Parity or Jump Parity Even PF JNP/JPO Jump No Parity or Jump Parity Odd PF JS Jump Sign (negative value) SF JNS Jump No Sign (positive value) SF
- 11. Any Question?