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Logical, Bitwise, and Arithmetic Operations in Assembly Language

This lecture by Dr. Rajesh Palit, presented to EECS students at NSU, covers critical logical and bitwise operations, including AND, OR, XOR, and NOT, as well as shift/rotate instructions, and multiplication/division techniques in assembly language. The session emphasizes the importance of logic instructions for bit manipulation and the effects on the flag registers. Furthermore, arithmetic operations are explored with practical examples, providing students with foundational knowledge necessary for effective programming in assembly language.

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Logical, Bitwise, and Arithmetic Operations in Assembly Language

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  1. Lecture 5Logical, Bitwise, and Multiplication/Division Operations Presented By Dr. Rajesh Palit Asst. Professor, EECS, NSU Originally Prepared By Dr. ShazzadHosain, EECS, NSU

  2. Agenda • Logic Instructions • AND, OR, XOR and NOT • TEST Instruction • Shift and Rotate Instructions • Multiplication and Division

  3. AND, OR and XOR Instructions • AND destination, source • OR destination, source • XOR destination, source • Memory-to-memory operations are not allowed • Effect on flags • SF, ZF, PF reflect the result • CF, OF = 0

  4. Use of Logic Instructions • Selectively modify the bits of destination • b AND 1 = b (b represents a bit, 0/1) • b AND 0 = 0 • b OR 0 = b • b OR 1 = 1 • b XOR 0 = b • b XOR 1 = ~b (complement of b) • So, AND cab be used to clear specific destination bit • OR can be used to set specific destination bit • XOR can be used to complement specific destination bit

  5. Examples Example 7.2: Clear the sign bit of AL while leaving the other bits unchanged. AND AL, 7Fh Example 7.3: Set the msb and lsb of AL while preserving the other bits. OR AL, 81h Example 7.4: Change the sign bit of DX XOR DX, 8000h 0111 1111 = 7Fh 1000 0001 = 81h

  6. NOT Instruction Complement operation NOT destination Example 7.5: Complement the bits in AX NOT AX

  7. Agenda • Logic Instructions • AND, OR, XOR and NOT • TEST Instruction • Shift and Rotate Instructions • Stack Operations • Introduction to Procedures

  8. TEST Instruction • TEST performs AND on the destination • TEST destination, source • Effects on flags • SF, ZF, PF reflect the result • AF is undefined • CF, OF = 0 • TEST vs. CMP • CMP is subtraction operation

  9. TEST Example • Jump to label BELOW if AL contains an even number TEST AL, 1 ; is AL even? JZ BELOW ; yes, go to BELOW

  10. Agenda • Logic Instructions • AND, OR, XOR and NOT • TEST Instruction • Shift and Rotate Instructions • Stack Operations • Introduction to Procedures

  11. Shift and Rotate Instructions • Two types of shift and rotate instructions • Logical Shift / Rotate • Arithmetic Shift/Rotate • Both logical and arithmetic left shift are identical • But right shifts are different

  12. Shift and Rotate Instructions SHL DH, 3 ; DH = 1110 1111 SHR DH, 3 ; DH = 1110 1111 DH = 0111 1000 DH = 1011 1100 DH = 0001 1101 DH = 1111 1011 C = 1 C = 1 C = 1 C = 1 SAL DH, 2 ; DH = 1110 1111 SAR DH, 2 ; DH = 1110 1111

  13. Rotate Instructions Let DH = 8Ah = 1000 1010 CF = 1 After first RCR DH = 1100 0101 CF = 0 After second RCR DH = 0110 0010 CF = 1

  14. Multiplication / Division • Unsigned Integers MUL / DIV • Signed Integers IMUL / IDIV • A = 1000 0000 => 128 -128 • B = 1111 1111 => 255 -1 • Unsigned AxB = 0111 1111 1000 0000 34640 • Signed AXB = 0000 0000 1000 0000 128

  15. Multiplication • MUL source • source is 8/16 bit reg/mem • source can’t be a immediate value • Multiplicand is assumed to be in AL/AX • source x AL = AX • Source x AX = DX:AX • CF/OF – 0, 1 MUL upper-half = 0 / non-zero • For IMUL, CF/OF 0 means signed extension of the lower half, 1 means otherwise

  16. ARITHMETIC EXPRESSION • A = 5 x A – 12 x B • A dw 10 • B dw20 • MOV AX, 5 • IMUL A • MOV A, AX • MOV AX, 12 • IMUL B • SUB A, AX

  17. Factorial Calculation MOV AX, 1 MOV CX, 5 TOP: MUL CX LOOP TOP

  18. Division • DIV and IDIV • DIV divisor • divisor is 8/16 bit reg/mem, not immidiate value • dividend is in AX or DX:AX • Quotient is in AL/AX • Remainder is in AH/DX • Divide Overflow

  19. Assignment - 1 • String to number • Perform Arithmetic Operations

  20. References • Ch 7, Assembly Language Programming – by CharlsMarut • Ch 4, Intel Microprocessors – by Brey

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