MIPS assembly progr.-factorial calculation

Click For Summary

Discussion Overview

The discussion revolves around writing a MIPS assembly program to calculate the factorial of a number, specifically focusing on issues encountered during coding, debugging, and obtaining correct results. Participants share their code snippets and seek assistance with errors and unexpected outputs.

Discussion Character

  • Technical explanation
  • Debugging
  • Exploratory
  • Debate/contested

Main Points Raised

  • One participant reports an "Exception 6 [Bad instruction address]" error when running their initial code and seeks help in identifying the issue.
  • Another participant suggests using a debugger in PCSpim to single-step through the code to locate the problematic line and notes the absence of labels in the data section as a potential issue.
  • A participant mentions that after modifying their code, they encounter incorrect results, specifically a large, unexpected number, and suspects memory allocation issues in the stack.
  • One participant tests the code with a smaller input (3) to verify functionality and observes that the output is still incorrect, indicating a possible problem with how values are stored and retrieved in the program.
  • Another participant highlights that the output seems to be loading an address instead of the intended value, leading to confusion about the algorithm's correctness.
  • Participants express frustration with the complexity of assembly programming and the challenges of debugging their code.

Areas of Agreement / Disagreement

There is no consensus on the specific errors in the code or the best approach to resolve the issues. Multiple competing views on debugging strategies and coding practices are presented, and the discussion remains unresolved regarding the correct implementation of the factorial calculation.

Contextual Notes

Participants note limitations in their code related to memory allocation and the use of labels, which may affect the program's functionality. There are unresolved questions about the algorithm's logic and the handling of register values during execution.

Who May Find This Useful

This discussion may be useful for individuals learning MIPS assembly programming, particularly those interested in debugging techniques and factorial calculations in assembly language.

electra123
Messages
4
Reaction score
0
I'm trying to write a MIPS assembly program that implements the calculation of n! Well i wouldn't be here if i were successful.When i try to run the following code on PCSpim this appears on the screen:
"Exception 6 [Bad instruction address] occurred and ignored"
Can anyone help me find my errors?i think my head is going to explode!

Thanks in advance...

Here is my code:

.data 0x10008000
.word 10
.word 1
.word 0
.ascii "The factorial of 10 is %d \n"
.text
.globl main

main:
addi $sp,$sp,-8
sw $ra,4($sp)
sw $fp,8($sp)
addiu $fp,$sp,4
lw $a0,4($gp)
jal fact

move $a1,$v0

jal printf
lw $ra,4($sp)
lw $fp,8($sp)
addi $sp,$sp,8
jr $ra

fact:
addi $sp,$sp,-8
sw $ra,4($sp)
sw $fp,8($sp)
addiu $fp,$sp,4
sw $a0,0($fp)

lw $v0,0($fp)

move $t0,$zero
slti $t0,$v0,1
beq $t0,$zero,L2
addi $v0,$zero,1
jr L1





L1:
lw $ra,4($sp)
lw $fp,8($sp)
addiu $sp,$sp,8
jr $ra

L2:
lw $v1,0($fp)
subu $v0,$v1,1
move $a0,$v0
jal fact
lw $v1,0($fp)
mul $v0,$v0,$v1


printf:
li $v0,4
la $a0,12($gp)
syscall

li $v0,1
move $a0,$v1
syscall
 
Technology news on Phys.org
Can you identify the line of code that causes the exception? There should be a debugger in PCSPIM that you can use to single-step through your code.

One thing that seems odd to me is that you have some data with no labels.
Here's some MIPS code that uses labels:
Code: 
	.data 	0x10000100
first:		.word	0
last:		.word	0
mid:		.word	0
 
Well thank you very much for your respond but I've changed my code and now I'm facing a false result/calculation .I guess that in my previous program there was a problem with memory allocation in the stack.The reason i have these (.data 0x10008000 .word 10) is because i wanted for example to calculate 10!When I am running my new code though, i come up with an odd result(a very big obscure number)
i've been working on this new improved code for the last 8 hours with no results!Take a look if you want to help me.Thanks in advance :)
Here's my new code!
Code: 
.data 0x10008000
.word 10
.word 1
.word 0
.ascii "The factorial of 10 is %d \n"
.text
.globl main

main:
                addi $sp,$sp,-32
	        sw $ra,20($sp)
                sw $fp,16($sp) 
                addiu $fp,$sp,28
	        lw $a0,0($gp) #$a0=10
	        jal fact
                
                add $a1,$v0,$zero
                
                jal printf

	        lw $ra,20($sp)
                lw $fp,16($sp)
	        addi $sp,$sp,32
	        jr $ra
               
fact:         
                addi $sp,$sp,-32
	        sw $ra,20($sp)
                sw $fp,16($sp) 
                addiu $fp,$sp,28
            
	        sw $a0,0($fp)
  
                lw $v0,0($fp)
	
                li $t0,1
                slti $t1,$v0,1
	        bne $t1,$t0,L2
	        addi $v0,$zero,1
                jr L1
		
L1:
                lw $ra,20($sp)
                lw $fp,16($sp)
                addiu $sp,$sp,32
                jr $ra

L2:
                 lw $v1,0($fp)
                 addi $v0,$v1,-1
                 add  $a0,$v0,$zero
                 jal fact
                 lw $v1,0($fp)
                 mul $v0,$v0,$v1                
                 
   
printf:
    
    li $v0,4
    la $a0,12($gp)
    syscall
    
    li $v0,1	
    add $a0,$a1,$zero
    syscall
 
Last edited:
electra123 said:
Well thank you very much for your respond but I've changed my code and now I'm facing a false result/calculation .I guess that in my previous program there was a problem with memory allocation in the stack.The reason i have these (.data 0x10008000 .word 10) is because i wanted for example to calculate 10!
I get it that you want to calculate 10!, but my question was, why aren't you using labels for your data values?
electra123 said:
When I am running my new code though, i come up with an odd result(a very big obscure number)
I tried running your code using QtSpim, which I believe is a more recent version.

So I wouldn't have to single-step through so much code, I changed the value from 10 to 3, which should return 6.

I don't know exactly what your problem is, but I can't figure out where you code is storing its computed values (that's where using labels for your data would be helpful!).

I get the same bogus value that you did, 2147482573, that is output in the last couple of lines of your printf routine.

Code: 
    li $v0,1	
    add $a0,$a1,$zero
    syscall

Using the debugger, I see that the values in the relevant registers are as follows:
a0: 7ffffb2c
v0: 1 (this is the value for syscall to print an int)

It seems that you are loading a0 with an address rather than the value to print. If I check memory location 7ffffb2c, I see the value (as decimal) 2147482573.

For me, since I was calculating 3!, the code should have displayed 6, but I don't see that 6 has been stored anywhere.

I don't understand your algorithm well enough to follow what you're trying to do. I would strongly urge you to use the debugger so that you can figure out why you aren't getting the right value. For testing, try a smaller value. If you can revise your code so that it will calculate, say, 3!, it will likely work for 10! as well.
electra123 said:
i've been working on this new improved code for the last 8 hours with no results!Take a look if you want to help me.Thanks in advance :)
Here's my new code!
Code: 
.data 0x10008000
.word 10
.word 1
.word 0
.ascii "The factorial of 10 is %d \n"
.text
.globl main

main:
                addi $sp,$sp,-32
	        sw $ra,20($sp)
                sw $fp,16($sp) 
                addiu $fp,$sp,28
	        lw $a0,0($gp) #$a0=10
	        jal fact
                
                add $a1,$v0,$zero
                
                jal printf

	        lw $ra,20($sp)
                lw $fp,16($sp)
	        addi $sp,$sp,32
	        jr $ra
               
fact:         
                addi $sp,$sp,-32
	        sw $ra,20($sp)
                sw $fp,16($sp) 
                addiu $fp,$sp,28
            
	        sw $a0,0($fp)
  
                lw $v0,0($fp)
	
                li $t0,1
                slti $t1,$v0,1
	        bne $t1,$t0,L2
	        addi $v0,$zero,1
                jr L1
		
L1:
                lw $ra,20($sp)
                lw $fp,16($sp)
                addiu $sp,$sp,32
                jr $ra

L2:
                 lw $v1,0($fp)
                 addi $v0,$v1,-1
                 add  $a0,$v0,$zero
                 jal fact
                 lw $v1,0($fp)
                 mul $v0,$v0,$v1                
                 
   
printf:
    
    li $v0,4
    la $a0,12($gp)
    syscall
    
    li $v0,1	
    add $a0,$a1,$zero
    syscall
 
Thank you very much for taking a look into this abysmal code :) i appreciate it!im going to work it again ,more serious this time!god...i hate assembly
 

Similar threads

Solving MIPS Runtime Error: Address Out of Range 0x00000000
  • · Replies 1 ·
Replies
1
Views
11K
MIPS Help (converting numbers to diff bases)
  • · Replies 5 ·
Replies
5
Views
10K
Why does this MIPS program do what it does?
  • · Replies 4 ·
Replies
4
Views
2K
Printing an array of char to a string in MIPS
  • · Replies 1 ·
Replies
1
Views
15K
Converting numerical input to corresponding string using MIPS
  • · Replies 1 ·
Replies
1
Views
8K
Help with MIPS Decimal to any base
  • · Replies 1 ·
Replies
1
Views
2K
Mips swapping without temp variable
  • · Replies 1 ·
Replies
1
Views
8K
Engineering MIPS - Fibonacci Series: Main and fib function
  • · Replies 4 ·
Replies
4
Views
5K
MIPS - write a function to remove blanks
  • · Replies 1 ·
Replies
1
Views
10K
Solving MIPS Programming: Enter 5 Ints & Reverse Order
  • · Replies 1 ·
Replies
1
Views
3K