build your own assembler that reads the R/I/J Format Instructions of MIPS I-Form

Question

build your own assembler that reads the R/I/J Format Instructions of MIPS

I-Format (Data transfer, branch format)

op rs rt address 6 bits 5 bits 5 bits 16 bits

J-Format (Jump instruction format)

op address 6 bits 26 bits

R-Format (Arithmetic instruction format)

op rs rt rd shamt funct 6 bits 5 bits 5 bits 5 bits 5 bits 6 bits

using the template below:

#include <stdio.h>

#define MAXLINE 80
#define MAXREG 5

int main()
{
char line[MAXLINE]={0};
char oper[MAXLINE];
char rd[MAXREG],rs[MAXREG],rt[MAXREG];

while (fgets(line, MAXLINE, stdin)) {
/* check if a 3-address R format instruction */
if (sscanf(line, "%s $%[^,],$%[^,],$%s", oper, rd, rs, rt) == 4) {
printf("input line: %s ", line);
printf("parsed line: op:%10s rd:%5s rs:%5s rt:%5s ",
oper, rd, rs, rt);
}
/* you need to add other patterns for R,I,and J encoding */
else {
printf("input line: %s ", line);
printf("you need to add sscanf format ");
}
}
return 0;
}

Explanation / Answer

MIPS code:-

$LFB0 = .

main:

addiu $sp,$sp,-224

sw $31,220($sp)

sw $fp,216($sp)

move $fp,$sp

addiu $2,$fp,32

li $3,80 # 0x50

move $6,$3

move $5,$0

move $4,$2

jal memset

nop

lui $2,%hi(stdin)

lw $2,%lo(stdin)($2)

nop

move $6,$2

li $5,80 # 0x50

addiu $2,$fp,32

move $4,$2

jal fgets

nop

sltu $2,$0,$2

andi $2,$2,0x00ff

beq $2,$0,$L2

nop

addiu $4,$fp,192

addiu $3,$fp,112

addiu $2,$fp,208

sw $2,20($sp)

addiu $2,$fp,200

sw $2,16($sp)

move $7,$4

move $6,$3

lui $2,%hi($LC0)

addiu $5,$2,%lo($LC0)

addiu $2,$fp,32

move $4,$2

jal sscanf

nop

xori $2,$2,0x4

sltu $2,$2,1

andi $2,$2,0x00ff

beq $2,$0,$L3

nop

addiu $2,$fp,32

move $5,$2

lui $2,%hi($LC1)

addiu $4,$2,%lo($LC1)

jal printf

nop

addiu $5,$fp,200

addiu $4,$fp,192

addiu $3,$fp,112

addiu $2,$fp,208

sw $2,16($sp)

move $7,$5

move $6,$4

move $5,$3

lui $2,%hi($LC2)

addiu $4,$2,%lo($LC2)

jal printf

nop

b $L5

nop

addiu $2,$fp,32

move $5,$2

lui $2,%hi($LC1)

addiu $4,$2,%lo($LC1)

jal printf

nop

lui $2,%hi($LC3)

addiu $4,$2,%lo($LC3)

jal puts

nop

b $L5

nop

move $2,$0

move $sp,$fp

lw $31,220($sp)

lw $fp,216($sp)

addiu $sp,$sp,224

j $31

nop

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