Lecture 5 Logical Bitwise and MultiplicationDivision Operations Presented

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

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

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

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

Examples Example 7. 2: Clear the sign bit of AL while leaving the other bits unchanged. AND AL, 7 Fh 0111 1111 = 7 Fh Example 7. 3: Set the msb and lsb of AL while preserving the other bits. OR AL, 81 h 1000 0001 = 81 h Example 7. 4: Change the sign bit of DX XOR DX, 8000 h

NOT Instruction Complement operation NOT destination Example 7. 5: Complement the bits in AX NOT AX

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

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

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

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

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

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

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

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

Multiplication • • MUL 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

ARITHMETIC EXPRESSION • A = 5 x A – 12 x B • A dw 10 • B dw 20 • MOV AX, 5 • IMUL A • MOV A, AX • MOV AX, 12 • IMUL B • SUB A, AX

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

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

Assignment - 1 • String to number • Perform Arithmetic Operations

References • Ch 7, Assembly Language Programming – by Charls Marut • Ch 4, Intel Microprocessors – by Brey