MIPS : loop goes to infinity - c++

Question

I am trying to convert this c++ function to mips. I think I am having problem in loop because when I run it, it gives me 13..1.17.5.. but my output should be two ip addresses : 130.52.0.10 and 171.9.50.186
C++ function code :
void IPtoDD(int arg0, char *arg1)
{
int temp, numChar, shift = 24;
for (int i=0; i<4; i++) {
temp = arg0 >> shift;
temp = temp & 0x000000ff;
numChar = byteToDec(temp,arg1);
arg1 += numChar;
*arg1++ = '.';
shift -= 8;
}
arg1--;
*arg1 = 0;
return;
}
MIPS code :
IPtoDD: addi $sp, $sp, -20
sw $ra, ($sp)
sw $s0, 4($sp)
sw $s1, 8($sp)
sw $s2, 12($sp)
sw $s3, 16($sp)
move $s0, $a0
move $s1, $a1
li $s3, 24 #s3=shift
li $s2, 0 #s2=i
li $t5, 0 #t5=temp
li $t3, 0
move $s1, $a1 #s1=*arg1
loop: srl $t5, $s0, $s3 #t3= numChar
and $t5, $t5, 0xff #t4= (*arg1)
move $a0, $t5
move $a1, $s1
jal byteToDec
move $t3, $v0
add $s1, $s1, $t3
li $t5, '.'
sb $t5, ($a1)
addi $a1, $a1, 1
addi $s3, $s3, -8
addi $s2, $s2, 1
blt $s2, 4, loop
addi $s1, $s1, -1
sb $0, ($a1)
lw $s3, 16($sp)
ra: lw $s2, 12($sp)
lw $s1, 8($sp)
lw $s0, 4($sp)
lw $ra, ($sp)
addi $sp, $sp, 20
jr $ra
Could please help out here. I tried a lot but not able make it run correctly.
edit:
C++ function for byteToDec
int byteToDec(int arg0, char *arg1)
{
int temp, flag = 0, count = 0;
if (arg0==0) {
*arg1 = '0';
return 1;
}
else {
temp = arg0/100;
if (temp != 0) {
*arg1++ = (char) temp + 0x30;
count++;
flag = 1;
}
temp = (arg0 % 100) / 10;
if ((flag!=0) || (temp != 0)) {
*arg1++ = (char) temp + 0x30;
count++;
}
temp = arg0 % 10;
*arg1 = (char) temp + 0x30;
count++;
return count;
}
}
byteToDec in MIPS:
byteToDec: #t0= temp
#t1= flag
#v0= count
#t3= (*arg1)
bne $a0, $0, else
li $t3, '0'
sb $t3, ($a1)
li $v0, 1
jr $ra
else: div $t0, $a0, 100
beq $t0, 0, cont
bp2: addi $t3, $t0, 0x30
sb $t3, ($a1)
addi $a1, $a1, 1
addi $v0, $v0, 1
li $t1, 1
cont: rem $t3, $a0, 100
div $t0, $t3, 10
bne $t1, 0, nxtIf
beq $t0, 0, endElse
nxtIf: addi $t3, $t0, 0x30
sb $t3, ($a1)
addi $a1, $a1, 1
addi $v0, $v0, 1
endElse:rem $t0, $a0, 10
bp1: addi $t3, $t0, 0x30
sb $t3, ($a1)
addi $v0, $v0, 1
ra1: jr $ra

Answer 1

You are using t3 as your loop counter and then trashing t3 in your byteToDec function. MIPS convention is that t registers are "temp" and not to be used across function calls like that. You should put your loop variable in a s register (a "save" register), and if your called function needs to reuse that same s register, it needs to save it to the stack or something and restore the value before returning to the callee.

Answer 2

I Have a program and it the first loop works ell but the second to 6th loop goes to inf. I'm a beginner and could use some help
#include <iostream>
#include <cmath>
#include <fstream>
using namespace std;
ofstream myfile ("Atomseries.txt");
int main()
{
float rconstant=109677.58;
int nstart, nend;
int length;
for (nstart = 1; nstart <= 6; nstart++){
for (nend= 2; nend <=nstart + 10; nend++)
length = 1/(rconstant*(1/(nstart*nstart)- 1/(nend*nend)));
myfile << length * 10000000 << endl;
}
if (nstart = 1)
myfile << "Lyman Series"<< endl;
else
;
if (nstart = 2)
myfile << "B Series" << endl;
else
;
if (nstart= 3)
myfile << " series"<< endl;
return 0;
}