Assembly Language Lab # 4 Data Transfer & Arithmetic (1)

Transcription

1 Faculty of Engineering Computer Engineering Department Islamic University of Gaza 2011 Assembly Language Lab # 4 Data Transfer & Arithmetic (1) Eng. Mohammad Elhindi

2 Assembly Language Lab # 4 Data Transfer & Arithmetic (1) Objective: To be familiar with Assembly Language Introduction: 1. Data Transfer MOV Instruction Move from source to destination. Note that : No more than one memory operand permitted, the registers CS, EIP, and IP cannot be the destination and No immediate to segment moves Syntax: MOV destination,source MOVZX When you copy a smaller value into a larger destination, the MOVZX instruction fills (extends) the upper half of the destination with zeros. Syntax: MOVZX destination,source MOVSX The MOVSX instruction fills the upper half of the destination with a copy of the source operand's sign bit. 2

3 Syntax: MOVSX destination,source XCHG Instruction XCHG exchanges the values of two operands. At least one operand must be a register. No immediate operands are permitted. 2. Arithmetic( Adding and Subtracting Numbers) INC destination destination destination + 1 Add 1 from destination operand,operand may be register or memory DEC destination destination destination 1 subtract 1 from destination operand,operand may be register or memory ADD instruction Previous labs have already used the ADD instruction. The form of the ADD instruction is: ADD destination, source ;dest operand = dest operand + source operand The destination operand can be a register or in memory. The source operand can be a register, in memory or immediate. Flags: ZF = 1 iff dest + src = 0 SF = 1 iff dest + src < 0 CF = 1 iff dest + src generated carry out of most significant bit OF = 1 iff dest + src resulted in signed overflow AF = 1 iff when an operation produces a carry out from bit 3 to bit 4 PF = 1 iff an instruction generates an even number of 1 bits in the low byte of the destination operand. 3

4 SUB instruction SUB dest, source ;dest = dest source Flags: ZF = 1 iff dest - src = 0 SF = 1 iff dest - src < 0 CF = 1 iff required a borrow at most-significant-bit OF = 1 iff resulted in signed overflow AF = 1 iff resulted in borrow into the low-ordered four bit of 8-,16-, or 32-bit operands PF = 1 iff an instruction generates an even number of 1 bits in the low byte of the destination operand. NEG (negate) Instruction Reverses the sign of an operand. Operand can be a register or memory operand. Lab work: Exercise 1: Exchange the content of the following variables Var1 dw 1000h Var2 dw 2000h 4

5 Exercise 2: Write a code to increment the odd elements in the array numbers and decrement the even elements on the same array Numbers 1, 2, 3, 4 Exercise 3: Debug the following code to find which flags will be after each instructions from these flags (CF, ZF, OF, SF) mov ax,7ffoh add al,1oh add ah,1 add ax,2 Exercise 4: Write an assembly code that perform the following addition val1= (-Al+ Bl) - va12. Consider the following intialization val1 db?? val2 db 23 mov al,17 mov bl,29 5

6 Homework: H.W1: Write an assembly code to put the byte array Vowels in the double word array New_Vowels in the opposite direction Vowels db a,e,i,o,u New_Vowels dd 5 dup(?) Then print the content of array New_Vowels H.W2: Use the array odd to find the square of the numbers between 1 and 5 and put the square of each number in the array square odd db 1,3,5,7,9 square 5 dup(?) H.W3: How can you calculate the result of 7FFFh+FFFFh without causing the carry flag to be set 6