multiplication and division with marie

Question

where is the mistake here , exactly in the the division , it returns the value of input x not return the result of the division

ORG 100 
Input
store x
input
store y
/ Summation 
Load x
Add y 
Store sum
/Output of the Summation
Load sum
Output
/ Subtraction
Load x
Subt y
Store sub
/Output of the subtraction
Load sub
Output
/ Multiplication
multloop, Load x
Add multi
Store multi
Load y
Subt one
Store y
Skipcond 400
Jump multloop
/Output of the multiplication
Load multi
Output
/ Division
Load zero 
Store quotient
divloop, Load x
Subt y
Skipcond 800
Jump Adding
Jump output
Adding, Store x
Load quotient
Add one
Store quotient
Jump divloop
/Output of Division
output, Load x
Store quotient
Load quotient
Output
Halt 
/ Variable Declarations
x, dec 0
y, dec 0
one, dec 1
remainder, dec 0
quotient, dec 0
sum, dec 0
sub, dec 0
multi, dec 0
zero, dec 0

• Jester: output, Load x; Store quotient of course it prints x (also note you decrement x in the loop, so it's actually the remainder) Skipcond 800 should be Skipcond 000, you want to skip looping if the result is negative.
• Jester: Furthermore the multiplication loop already decrements y to zero so your division will not work.
• Erik Eidt: Assembly programmers, especially beginners, need know how to use a debugger to see what's going on inside during the execution of their programs. If you don't know how to use a debugger, now is a good time to learn.

Answer 1

There are a few issues:

• The multiplication part:

  • does not account for the case where the the input y is 0. In that scenario the exit condition will be false for the next 65535 iterations of the loop! You should check the loop-exit condition before making any updates.

  • does not reset multi back to 0 before starting. This is important when the program is reset back to the top after it has already executed code. In that case the variables maintain their values. So do like you did for the division section and set multi to zero before the loop starts

  • modifies y. This is problematic as the next section of your program (division) needs the original value of y. So make sure not to modify it anywhere in your program. Instead of decrementing y, first copy its value to another variable (like count) and decrement that variable instead.

• The division part:

  • modifies x. See previous point. Here it is less of a problem, as the division part is the last section in your program, but it would make sense to apply the same rule here: don't modify the input variables, but instead use another variable. You already defined remainder, but you didn't use it. It can serve this purpose.

  • Skipcond 800 is the wrong condition. You need Skipcond 000 here, or else swap the Jump statements that follow it.

Other remarks

Not problematic, but:

• your program has no good use for the variables sum and sub. The value that is written to sum is immediately read back from it, which is a useless operation when you have no other purpose for it. Same for sub

• Many seem to add ORG 100 at the front of their code. It really is not needed.

• If the second input is 0, and the first not, the division loop will get into an infinite loop. This is not wrong, as division by 0 is undefined, but you could add a check for this condition and output some specific value, like 0.

Here is a version of your code with the above points taken into account:

 Input
 Store x
 Input
 Store y
 / Summation 
 Add x 
 Output
 / Subtraction
 Load x
 Subt y
 Output
 / Multiplication
 Load zero
 Store multi / Initialise
 Load y
 Store count / Don't modify y! Use different variable
multloop, Load count / First test the loop condition before any update
 Skipcond 800
 Jump multout
 Subt one
 Store count
 Load x
 Add multi
 Store multi
 Jump multloop
 
 / Output of the multiplication
multout, Load multi
 Output
 / Division
 Load zero
 Store quotient
 Load x
 Store remainder / Don't update x! Use different variable
 Load y / Check for division by 0
 Skipcond 400
 Jump divloop
 Jump output
divloop, Load remainder
 Subt y
 Skipcond 000 / Fix
 Jump Adding
 Jump output
Adding, Store remainder
 Load quotient
 Add one
 Store quotient
 Jump divloop
 / Output of Division
output, Load quotient
 Output
 Halt 
/ Constant Declarations
zero, Dec 0
one, Dec 1
/ Variable Declarations
x, Dec 0
y, Dec 0
remainder,Dec 0
quotient, Dec 0
multi, Dec 0
count, Dec 0

Run it on MARIE.org