Structures and Macros - Computer Organization and Assembly Language - Lecture Slides, Slides of Assembly Language Programming

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Computer Organization &

Assembly Languages

Structures & Macros

Overview

 Structures

 Macros

 Conditional-Assembly Directives

 Defining Repeat Blocks

Structure

 A template or pattern given to a logically related

group of variables.

 field - structure member containing data

 Program access to a structure:

 entire structure as a complete unit

 individual fields

 Useful way to pass multiple related arguments to a

procedure

 example: file directory information

Using Structure

 Structures in assembly are essentially the same as

structures in C and C++

 Using a structure involves three sequential steps:

1. Define the structure.

2. Declare one or more variables of the structure type,

called structure variables.

3. Write runtime instructions that access the structure.

Employee Structure

Employee STRUCT

IdNum BYTE "000000000"

LastName BYTE 30 DUP(0)

Years WORD 0

SalaryHistory DWORD 0,0,0,

Employee ENDS

A structure is ideal for combining fields of

different types:

"000000000" (null) 0 0 0 0 0 Lastname SalaryHistory

Years

Idnum

initializers

Declaring Structure Variables

 Structure name is a user-defined type

 Insert replacement initializers between brackets or

braces:

<... > or {... }

 Empty brackets <> retain the structure's default

field initializers (or braces {})

 Examples:

.data

point1 COORD <5,10>

point2 COORD <>

worker Employee <>

Array of Structures

 An array of structure objects can be defined using

the DUP operator.

 Initializers can be used

NumPoints = 3 AllPoints COORD NumPoints DUP(<0,0>)

RD_Dept Employee 20 DUP(<>)

accounting Employee 10 DUP(<,,,4 DUP(20000) >)

Referencing Structure Variables

.data worker Employee <>

mov eax,TYPE Employee ; 57 mov eax,SIZEOF Employee ; 57 mov eax,SIZEOF worker ; 57 mov eax,TYPE Employee.SalaryHistory ; 4 mov eax,LENGTHOF Employee.SalaryHistory ; 4 mov eax,SIZEOF Employee.SalaryHistory ; 16

Employee STRUCT ; bytes IdNum BYTE "000000000" ; 9 LastName BYTE 30 DUP(0) ; 30 Years WORD 0 ; 2 SalaryHistory DWORD 0,0,0,0 ; 16 Employee ENDS ; 57

Looping Through An Array of Points

.data NumPoints = 3 AllPoints COORD NumPoints DUP(<0,0>)

.code mov edi,0 ; array index mov ecx,NumPoints ; loop counter mov ax,1 ; starting X, Y values L1: mov (COORD PTR AllPoints[edi]).X,ax mov (COORD PTR AllPoints[edi]).Y,ax add edi,TYPE COORD inc ax Loop L

Sets the X and Y coordinates of the AllPoints array to

sequentially increasing values (1,1), (2,2), ...

Example: Displaying System Time

 Retrieves and displays the system time at a

selected screen location using Windows functions.

 How to obtain the system time?

SYSTEMTIME Structure in Assembly

SYSTEMTIME STRUCT

wYear WORD?

wMonth WORD?

wDayOfWeek WORD?

wDay WORD?

wHour WORD?

wMinute WORD?

wSecond WORD?

wMilliseconds WORD?

SYSTEMTIME ENDS

Moving Cursor

 How to move cursor to a selected position?

Example: Displaying System Time

 Uses a Windows API call to get the standard console

output handle. SetConsoleCursorPosition positions

the cursor. GetLocalTime gets the current time of day:

.data

sysTime SYSTEMTIME <>

XYPos COORD <10,5>

consoleHandle DWORD?

.code

INVOKE GetStdHandle, STD_OUTPUT_HANDLE

mov consoleHandle,eax

INVOKE SetConsoleCursorPosition,

consoleHandle, XYPos

INVOKE GetLocalTime, ADDR sysTime

Example: Displaying System Time

 Display the time using library calls:

mov edx,OFFSET TheTimeIs ; "The time is " call WriteString movzx eax,sysTime.wHour ; hours call WriteDec mov edx,offset colonStr ; ":" call WriteString movzx eax,sysTime.wMinute ; minutes call WriteDec mov edx,offset colonStr ; ":" call WriteString movzx eax,sysTime.wSecond ; seconds call WriteDec