![• Operation Performed :--
• ES:[DI] DS:[SI]
• If a byte movement,
–For DF =0, SI SI +1 & DI DI +1
–For DF =1, SI SI -1 & DI DI - 1
• If a word movement,
–For DF =0, SI SI +2 & DI DI +2
–For DF =1, SI SI -2 & DI DI - 2
MOVS/MOVSB/MOVSW (contd..)](https://image.slidesharecdn.com/chap8086string-200319141116/85/Chap-8086-string-5-320.jpg)
![• Operation Performed :--
• If a byte movement,
–AL DS:[SI]
–For DF =0, SI SI +1
–For DF =1, SI SI -1
• If a word movement,
–AX DS:[SI]
–For DF =0, SI SI +2
–For DF =1, SI SI -2
LODS/LODSB/LODSW (contd..)](https://image.slidesharecdn.com/chap8086string-200319141116/85/Chap-8086-string-10-320.jpg)
![• Operation Performed :--
• If a byte movement,
–ES:[DI] AL
–For DF =0, DI DI +1
–For DF =1, DI DI -1
• If a word movement,
–ES:[DI] AX
–For DF =0, DI DI +2
–For DF =1, DI DI -2
STOS/STOSB/STOSW (contd..)](https://image.slidesharecdn.com/chap8086string-200319141116/85/Chap-8086-string-15-320.jpg)
Chap 8086 string
- 1. String Manipulation Instructions – These are the instructions used for strings for string movement, Load, Store, Comparison and Scan. – A string is a series of bytes or a series of words in sequential memory locations. – A ‘B’ in the instruction mnemonic is used to specifically indicate that a string of bytes is to be acted upon. – A ‘W’ in the instruction mnemonic is used to specifically indicate that a string of words is to be acted upon.
- 2. MOVS/MOVSB/MOVSW Syntax :-- MOVS destination, source MOVSB MOVSW • The MOVS instruction is used to transfer a byte or a word from the source string to the destination string. •The source must be in the data segment and the destination in the extra segment. • The offset of the source byte or a word must be placed in SI register, which is represented as DS:SI and the offset of the destination byte or a word must be placed in DI register, which is represented as ES:DI
- 3. MOVS/MOVSB/MOVSW (contd..) •On the execution of the instruction, SI and DI are automatically adjusted by one to the next element of the source and destination. •If the Direction Flag is reset (DF = 0), the registers SI and DI will be incremented by one for the byte movement and incremented by two for the word movement. •If the Direction Flag is set (DF = 1), the registers SI and DI will be decremented by one for the byte movement and decremented by two for the word movement.
- 4. MOVS/MOVSB/MOVSW (contd..) •The DS:SI and ES:DI register must be loaded prior to the execution of the MOVS instruction. •MOVSB and MOVSW are the implicit instructions to move a byte or word string . •The instruction MOVSB is used to transfer a byte from the source to destination and the instruction MOVSW is used to transfer a word from the source to destination. •In multiple byte or word moves, the count must be loaded in CX register which functions as a counter.
- 5. • Operation Performed :-- • ES:[DI] DS:[SI] • If a byte movement, –For DF =0, SI SI +1 & DI DI +1 –For DF =1, SI SI -1 & DI DI - 1 • If a word movement, –For DF =0, SI SI +2 & DI DI +2 –For DF =1, SI SI -2 & DI DI - 2 MOVS/MOVSB/MOVSW (contd..)
- 6. MOVS D_STRING, S_STRINGMOVSB ; moves a byteMOVSW ; moves a word • Examples :-- MOV AX, DATA ; initialize DS and ES MOV DS,AX MOV ES,AX CLD ; Clear DF for incrementing SI and DI LEA SI, S_STRING ; initialize SI & DI LEA DI, D_STRING MOVS/MOVSB/MOVSW (contd..)
- 7. LODS/LODSB/LODSW Syntax :-- LODS source LODSB LODSW • The LODS instruction is used to transfer a byte or a word from the source string pointed by SI in DS to AL for byte or AX for word •The offset of the source byte or a word must be placed in SI register, which is represented as DS:SI
- 8. LODS/LODSB/LODSW (contd..) •On the execution of the instruction, SI is automatically adjusted by one to the next element of the source and destination. •If the Direction Flag is reset (DF = 0), the registers SI will be incremented by one for the byte movement and incremented by two for the word movement. •If the Direction Flag is set (DF = 1), the registers SI will be decremented by one for the byte movement and decremented by two for the word movement.
- 9. LODS/LODSB/LODSW (contd..) •On the execution of the instruction, SI is automatically adjusted by one to the next element of the source and destination. •If the Direction Flag is reset (DF = 0), the register SI will be incremented by one for the byte movement and incremented by two for the word movement. •If the Direction Flag is set (DF = 1), the register SI will be decremented by one for the byte movement and decremented by two for the word movement.
- 10. • Operation Performed :-- • If a byte movement, –AL DS:[SI] –For DF =0, SI SI +1 –For DF =1, SI SI -1 • If a word movement, –AX DS:[SI] –For DF =0, SI SI +2 –For DF =1, SI SI -2 LODS/LODSB/LODSW (contd..)
- 11. LODSW ; LOADS a word to AXLODS S_STRINGLODSB ; loads a byte to AL • Examples :-- MOV AX, DATA ; initialize DS and ES MOV DS,AX CLD ; DF =0 for Incrementing SI LEA SI, S_STRING ; initialize SI LODS/LODSB/LODSW (contd..)
- 12. STOS/STOSB/STOSW Syntax :-- STOS destination STOSB STOSW • The LODS instruction is used to transfer a byte or a word from AL for byte or AX for word to the destination string pointed by DI in ES. •The offset of the destination byte or a word must be placed in DI register, which is represented as ES:DI
- 13. STOS/STOSB/STOSW (contd..) •In the STOS instruction, the destination must be declared as either DB or DW. •STOSB and STOSW are the implicit instructions to load a byte or word string . •The instruction STOSB is used to store a byte from the source AL to destination and the instruction STOSW is used to store a word from the source AX to destination. •In multiple byte or word moves, the count must be loaded in CX register which functions as a counter.
- 14. STOS/STOSB/STOSW (contd..) •On the execution of the instruction, DI is automatically adjusted by one to the next element of the destination. •If the Direction Flag is reset (DF = 0), the register DI will be incremented by one for the byte movement and incremented by two for the word movement. •If the Direction Flag is set (DF = 1), the register DI will be decremented by one for the byte movement and decremented by two for the word movement.
- 15. • Operation Performed :-- • If a byte movement, –ES:[DI] AL –For DF =0, DI DI +1 –For DF =1, DI DI -1 • If a word movement, –ES:[DI] AX –For DF =0, DI DI +2 –For DF =1, DI DI -2 STOS/STOSB/STOSW (contd..)
- 16. STOSB ; Stores byte from AL to destination STOS D_STRING ; Stores a byte or word in AL or AX dep on D_string to D_string • Examples :-- MOV AX, DATA ; initialize ES MOV ES,AX CLD ; DF =0 for Incrementing SI LEA DI, D_STRING ; initialize DI STOSW ; Stores a word from AX to destination STOS/STOSB/STOSW (contd..)
- 17. CMPS/CMPSB/CMPSW Syntax :-- CMPS destination, source CMPSB CMPSW • The CMPS instruction is used to compare a byte or a word in the source string with a byte or a word in the destination string. •The source must be in the data segment and the destination in the extra segment. • The offset of the source byte or a word must be placed in SI register, which is represented as DS:SI and the offset of the destination byte or a word must be placed in DI register, which is represented as ES:DI
- 18. CMPS/CMPSB/CMPSW (contd..) •On the execution of the instruction, SI and DI are automatically adjusted by one to the next element of the source and destination. •If the Direction Flag is reset (DF = 0), the registers SI and DI will be incremented by one for the byte comparison and incremented by two for the word comparison. •If the Direction Flag is set (DF = 1), the registers SI and DI will be decremented by one for the byte comparison and decremented by two for the word comparison
- 19. CMPS/CMPSB/CMPSW (contd..) •The DS:SI and ES:DI register must be loaded prior to the execution of the CMPS instruction. •CMPSB and CMPSW are the implicit instructions to move a byte or word string . •The instruction CMPSB is used to compare a byte from the source with destination and the instruction CMPSW is used to compare a word in the source with destination. •In multiple byte or word comparison, the count must be loaded in CX register which functions as a counter. •All conditional flags are affected
- 20. • Operation Performed :-- • If dest string > source string then CF =0, ZF = 0, SF = 0 • If dest string < source string then CF =1, ZF = 0, SF = 1 • If dest string = source string then CF =0, ZF = 1, SF = 0 • If a byte comparison, – For DF =0, SI SI +1 & DI DI +1 – For DF =1, SI SI -1 & DI DI - 1 • If a word comparison, – For DF =0, SI SI +2 & DI DI +2 – For DF =1, SI SI -2 & DI DI - 2 CMPS/CMPSB/CMPSW (contd..)
- 21. CMPSW ; compares a wordCMPS D_STRING, S_STRINGCMPSB ; compares a byte • Examples :-- MOV AX, DATA ; initialize DS and ES MOV DS,AX MOV ES,AX CLD ; Clear DF for incrementing SI and DI LEA SI, S_STRING ; initialize SI & DI LEA DI, D_STRING CMPS/CMPSB/CMPSW (contd..)
- 22. SCAS/SCASB/SCASW Syntax :-- SCAS destination SCASB SCASW • The SCAS instruction is used to scan a byte or a word with a byte in AL or word in AX. •The offset of the destination byte or a word must be placed in DI register, which is represented as ES:DI
- 23. SCAS/SCASB/SCASW (contd..) •On the execution of the instruction, DI is automatically adjusted by one to the next element of the destination. •If the Direction Flag is reset (DF = 0), the register DI will be incremented by one for the byte scan and incremented by two for the word scan. •If the Direction Flag is set (DF = 1), the register DI will be decremented by one for the byte scan and decremented by two for the word scan
- 24. SCAS/SCASB/SCASW (contd..) •In the SCAS instruction, the destination must be declared as either DB or DW. •SCASB and SCASW are the implicit instructions to scan a byte or word in a string . •The instruction SCASB is used to scan a byte and the instruction SCASW is used to scan a word. •In multiple byte or word moves, the count must be loaded in CX register which functions as a counter.
- 25. • Operation Performed :-- • If byte in AL or word in AX > dest string byte or word then CF =0, ZF = 0, SF = 0 • If byte in AL or word in AX < dest string byte or word then CF =1, ZF = 0, SF = 1 • If byte in AL or word in AX = dest string byte or word then CF =0, ZF = 1, SF = 0 • If a byte scan, – For DF =0, SI SI +1 & DI DI +1 – For DF =1, SI SI -1 & DI DI - 1 • If a word scan, – For DF =0, SI SI +2 & DI DI +2 – For DF =1, SI SI -2 & DI DI - 2 SCAS/SCASB/SCASW (contd..)
- 26. • Examples :-- MOV AX, DATA ; initialize ES MOV ES,AX CLD ; DF =0 for Incrementing SI LEA DI, D_STRING ; initialize DI MOV AL,’V’ SCAS D_STRING ; Scans a byte or word in AL or AX dep on D_string to D_string SCASB ; Scans byte from AL to destination SCASW ; Scans a word from AX to destination SCAS/SCASB/SCASW (contd..)
- 27. REP (Instruction Prefix) The REP instruction prefix is used in string instructions and interpreted as “Repeat while not end of string” In REP prefix, CX register is loaded with the count. Operation performed :-- • While CX <>0, perform the string operation • CX CX - 1
- 28. REP (Instruction Prefix) contd.. Example :-- MOV AX,DATA MOV DS, AX MOV ES,AX CLD MOV CX, string _length LEA SI,S_STRING LEA DI,D_STRING REP CMPSB
- 29. REPE/REPZ (Instruction Prefix) The REPE instruction prefix is used in string instructions and interpreted as “Repeat while not end of string and string equal” (CX<>0 and ZF =1) In REPE prefix, CX register is loaded with the count. Operation performed :-- • While CX <>0 & ZF -1 , perform the string operation • CX CX - 1
- 30. REPE/REPZ (Instruction Prefix) contd.. Example :-- MOV AX,DATA MOV DS, AX MOV ES,AX CLD MOV CX, string _length LEA SI,S_STRING LEA DI,D_STRING REPE CMPSB JE ST_EQUAL NT_EQUAL: MOV AX, 01 JMP END ST_EQUAL: MOV AX, 00
- 31. REPNE/REPNZ (Instruction Prefix) The REPNE instruction prefix is used in string instructions and interpreted as “Repeat while not end of string and string not equal” (CX<>0 and ZF =0) In REPNE prefix, CX register is loaded with the count. Operation performed :-- • While CX <>0 & ZF = 0 , perform the string operation • CX CX - 1