How to swap contents of two variables with one register (asm-simulator toy ISA)?

Question

I am new in assembly I tried to move variables in this link https://schweigi.github.io/assembler-simulator/ I tried to change the content of char1 and char3

JMP start
char1: db "A"  
char2: db "B"
char3: db "C"
start:
    MOV A, [char1]
    MOV B, [char3]
    MOV [char3],A
    MOV [char1],B

now I want to do it only with one register ( without B ) , it is possible to define another variable but i didn't understand how to move the content between 2 variables
Could you please advise ?

How I can do it with 4 variables ? how I can move content between variables ? — user1365697, Dec 04 '21 at 17:21
One way with a single register is to push `A` onto the stack. — Weather Vane, Dec 04 '21 at 17:34
Push all except one onto the stack. Transfer the last one. Pop and store the others. — Weather Vane, Dec 04 '21 at 17:38
Related: [How does XOR variable swapping work?](https://stackoverflow.com/questions/249423/how-does-xor-variable-swapping-work) — Weather Vane, Dec 04 '21 at 17:42
Do you have to use 1 register? We don't need any registers (modulo stack pointer): `push [char1]; push [char2]; pop [char2]; pop [char1]` — Erik Eidt, Dec 04 '21 at 19:13
@ErikEidt that's good, but the `pop address` isn't supported by the [instruction set](https://schweigi.github.io/assembler-simulator/instruction-set.html) (as in my answer). — Weather Vane, Dec 04 '21 at 19:33

score 2 · Answer 1 · answered Dec 04 '21 at 17:53

2

Here is the (not recommended) XOR method

MOV A, [char1]
XOR A, [char3]
XOR [char1], A
XOR [char3], A

A discussion of the XOR method is here:

How does XOR variable swapping work?

answered Dec 04 '21 at 17:53

Weather Vane

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Problem is, your simulator [instruction set](https://schweigi.github.io/assembler-simulator/instruction-set.html) doesn't have that addressing mode. – Weather Vane Dec 04 '21 at 18:08

score 0 · Accepted Answer · answered Dec 04 '21 at 17:50

0

Thanks to Vane

    JMP start
char1: db "D"  
char2: db "O"
char3: db "G"
start:
    MOV A, [char1]  
    PUSH A 
        MOV A, [char3]
    MOV [char1], A
    POP A
    MOV [char3], A

answered Dec 04 '21 at 17:50

user1365697

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How to swap contents of two variables with one register (asm-simulator toy ISA)?

2 Answers2