3.3 Programming in code of Three-address Virtual Computer

y=a*b+d*c-f, where

a=5=5h=00000101

b=4=4h=00000100

c=20=14h=00010100

d=-5=-5h=11111011

f=-20=-14h=11101100

Example for VC: 32 bits memory word, 3-address computer, 256 words=>8 bits address

Operation: (A1)op(A2)=>A3

7…….0	31…28	27…24	23…16	15…….8	7……….0	Bit’s numeration
Data definition: integer (fixed point notation), long (32 bits-double word), in BRC (binary radix complement or 2’d complement)
10	0000	0000	0000 0000	0000 0000	0000 0101	a=5
11	0000	0000	0000 0000	0000 0000	0000 0100	b=4
12	0000	0000	0000 0000	0000 0000	0001 0100	c=20=14h
13	1111	1111	1111 1111	1111 1111	1111 1011	d=-5
14	1111	1111	1111 1111	1111 1111	1110 1100	f=-20
15	0000	0000	0000 0000	0000 0000	0000 0000	y=?
16	0000	0000	0000 0000	0000 0000	0000 0000	w=?
Address (hexadecimal)	Code of Operation	Mode	A1	A2	A3	Comments
20	0011	0000	0001 0011	0001 0010	0001 0110	d*c=>w
21	0011	0000	0001 0000	0001 0001	0001 0101	a*b=>y
22	0001	0000	0001 0101	0001 0110	0001 0101	y+w=>y
23	0010	0000	0001 0101	0001 0100	0001 0101	y-f=>y
24	0000	0000	0000 0000	0000 0000	0000 0000	End (stop)

Characteristics:

Data volume V_d=7*32 bits = 28 bytes.

Program volume V_p=5*32 bits = 20 bytes.

Time of execution T_ex=2(+/-)+2(*)+12 (access to memory).

4 Simulation program developing

Program to simulate the working of Virtual Computer can be written in any language. C++ programming language supports graphical output, different data types, classes and so. That is why the application of C++ is preferable.

4.1 User Interface

UI should support:

- main menu;

- menus for all modes;

- keyboard control.

Example below shows the main menu and keyboard control.

void main()

{

textbackground(0);

clrscr();

char ch='0';

while(ch!=27) //code of ESC

{

menu();

request();

ch=getch();

switch(ch)

{

case '1': about(); break;

case '2': load(); break;

case '3': mem(); break;

case '4': alu(1); break;

default: if (ch!=27)

{ window(30,10,50,13);

textbackground(GREEN);

clrscr(); gotoxy(2,2);

cprintf("Check key!!");

}

}

}

}

void menu()

{

window(1,1,80,3);

textbackground(BLUE);

clrscr();

textcolor(YELLOW);

gotoxy(2,2); cprintf("1 - about");

gotoxy(15,2); cprintf("2 - load file");

gotoxy(30,2); cprintf("3 - show memory");

gotoxy(50,2); cprintf("4 - show ALU");

gotoxy(70,2); cprintf("ESC - exit");

}

void request()

{

window(1,24,80,25);

textbackground(RED);

clrscr();

textcolor(YELLOW);

gotoxy(20,1); cprintf("Select mode and press corresponding key:");

}

Figure 4.1 – Example of a start window with a main menu and request

4.2 Memory simulation

There are 4 typical actions For memory

At first it’s necessary to define length of memory word, for example, 13 bits.

#define NW 13

Memory can be defined as array of characters:

char MEM[256][NW];

After this program for virtual computer have to be loaded to file, for example, with a name test1.dat. Let structure of file is:

- the first line consists 2 decimal numbers: start address of data (10h = 16) and number of data (5);

- next 5 lines – data in binary code: 7, 9, 10, -10 (for negative numbers a BRC is used), free memory word to store a result;

- the next line consists 2 decimal numbers: start address of program (20h = 32) and number of instructions (4);

- next 4 lines – instructions in binary code, last instruction (code of operation = 0) – STOP.

16 5

0000000000111

0000000001001

0000000001010

1111111110110

0000000000000

32 4

0001000010000

0011000010001

0010000011110

0000000000000

Let define working identifiers:

PC – start address of program;

DPTR – start address of data;

l_CSEG – number of instructions;

l_DSEG – number of data;

int PC,DPTR,l_CSEG,l_DSEG;

Function below shows an example of input test from a file to memory.

void inpt(FILE *f)

{

int i,j;

char ch;

fscanf(f,"%d",&DPTR);

fscanf(f,"%d",&l_DSEG);

for(i=0;i<l_DSEG; i++)

{

fscanf(f,"\n");

for(j=0;j<NW;j++)

{ ch=fgetc(f);

MEM[DPTR+i][j]=ch;

}

}

fscanf(f,"%d",&PC);

fscanf(f,"%d",&l_CSEG);

for(i=0;i<l_CSEG; i++)

{

fscanf(f,"\n");

for(j=0;j<NW;j++)

{ ch=fgetc(f);

MEM[PC+i][j]=ch;

}

}

}

#include <stdio.h>

#include <conio.h>

#define NW 13

int PC,DPTR,l_CSEG,l_DSEG;

char MEM[256][NW];

#include "inpt.cpp"

#include "mem_disp.cpp"

void main()

{ FILE *f1;

f1= fopen("test1.dat","r");

fr= fopen("Rez.dat","w+");

inpt(f1);//input test1

mem_disp(); //show CSEG and DSEG

getch();

fclose(f1);

}