Explain passing parameters using pointers, Computer Engineering

Assignment Help:

Q. Explain Passing Parameters Using Pointers ?

This method overcomes the drawback of using variable names directly in procedure. It uses registers to pass procedure pointers to desired data. Let's explain it more with the help of a program.

Program version 2:

DATA_SEG               SEGMENT

                        BCD DB   25h; Storage for BCD test value

BIN      DB?  ; Storage for binary value

DATA_SEG ENDS

STACK_SEG SEGMENT    STACK

DW 100 DUP (0)    ; Stack of 100 words

TOP_STACK LABEL    WORD

STACK_SEG ENDS

CODE_SEG SEGMENT

ASSUME CS: CODE_SEG, DS: DATA_SEG, SS: STACK_SEG

START:           MOV AX, DATA_SEG   ; Initialize data

MOV DS, AX   ; segment using AX register

MOV AX, STACK_SEG   ; initialize stack

MOV SS, AX; segment. Why stack?

MOV SP, OFFSET TOP_STACK; initialize stack pointer

; Put pointer to BCD storage in SI and DI prior to procedure call.

                        MOV SI, OFFSET BCD   ; SI now points to BCD_IN 

                        MOV DI, OFFSET BIN; DI points BIN_VAL 

                                                            ; (returned value)

                        CALL BCD_BINARY   ; Call the conversion 

                                                            ; Procedure

                        NOP     ; Continue with program

                                                            ; Here

; PROCEDURE     : BCD_BINARY Converts BCD numbers to binary. 

; INPUT     : SI points to location in memory of data

; OUTPUT     : DI points to location in memory for result

; DESTROYS    : Nothing

BCD_BINARY PROC NEAR

PUSHF     ; Save flag register 

PUSH AX; and AX registers

PUSH BX; BX  

PUSH CX; and CX

MOV AL, [SI]   ; Get BCD value from memory

                                     ; For conversion

MOV BL, AL   ; copy it in BL also

AND   BL, 0Fh   ; and mask to get lower 4 digits

AND AL, 0F0h; Separate upper 4 bits in AL

MOV CL, 04   ; initialize counter CL so that upper digit 

ROR AL, CL; in AL can be brought to lower 4 bit 

                                    ; Positions in AL

MOV BH, 0Ah   ; Load 10 in BH

MUL BH; Multiply upper digit in AL by 10

                                    ; The result is stored in AL

ADD AL, BL   ; Add lower BCD digit in BL to result of 

                                    ; Multiplication

; End of conversion, now restore the original values prior to call. All calls will be in 

; reverse order to save above. The result is in AL register.

MOV [DI], AL   ; Store binary value to memory

POP CX; Restore flags and

POP BX; registers

POP AX  

POPF    

RET    

BCD_BINARY ENDP

CODE_SEG ENDS

             END START

Discussion:

In the program written above DI points to BIN and SI points to the BCD. The instruction MOV AL, [SI] copies the byte pointed by SI to AL register. In the same manner MOV [DI], AL transfers result back to memory location which is pointed by DI. 

This scheme allows you to pass procedure pointers to data anywhere in memory. You can pass pointer to individual data element or a group of data elements such as strings and arrays. This scheme is used for parameters passing to BIOS procedures.


Related Discussions:- Explain passing parameters using pointers

How do you make an append query, Append query can be used if you would like...

Append query can be used if you would like to add new rows of data to an already active table. The process of making an append query follows these steps they are. ? Basic step

In a for loop, In a for loop, if the condition is missing, then, It is s...

In a for loop, if the condition is missing, then, It is supposed to be present and taken to be true.

When is a memory unit called as ram, When is a memory unit called as RAM? ...

When is a memory unit called as RAM? A memory unit is called as RAM if any location can be accessed for a read or writes operation in some fixed quantity of time that is indepe

Describe program control instructions, Q. Describe Program Control Instruct...

Q. Describe Program Control Instructions? These instructions specify conditions for altering the sequence of program execution or we can say in other words that the content of

Add multiple layout cells, Q. Add Multiple Layout Cells ? Next you will...

Q. Add Multiple Layout Cells ? Next you will add three layout cells below the logo cell you just created. Afterwards you will insert page's navigation buttons in these cells.

Data dictionary, data dictionary for online banking system in software engi...

data dictionary for online banking system in software engineering

What is exception, a. Explain about exception? When do they occur? Show usi...

a. Explain about exception? When do they occur? Show using an example how to give your own exception handler. b. Can you restrict the types of exception that a function can thro

Define ftp, FTP FTP (File Transfer Protocol) is the protocol used on th...

FTP FTP (File Transfer Protocol) is the protocol used on the Internet for sending files and is usually used for uploading / downloading files (web pages) to and from servers. T

What are the standard types of files produced, What are the standard types ...

What are the standard types of files produced? A PDF file is universally recognized by the internet and is also a secure image, given that an electronic footprint remains when

Define device interface, Define device interface. The buffer registers ...

Define device interface. The buffer registers DATAIN and DATAOUT and the status flags SIN and SOUT are part of circuitry commonly called as a device interface.

Write Your Message!

Captcha
Free Assignment Quote

Assured A++ Grade

Get guaranteed satisfaction & time on delivery in every assignment order you paid with us! We ensure premium quality solution document along with free turntin report!

All rights reserved! Copyrights ©2019-2020 ExpertsMind IT Educational Pvt Ltd