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I am required to write a factorial function in ARM assembly language that takes an integer $ n $ as input and returns the value of $ n! $. However, I can only use the $ 4 $ basic arithmetic operations $ + - * / $ (so no if-else or loop or recursion). Can anyone suggest a hint to do that? I can only do if I am allowed to use if-else or recursion.

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    $\begingroup$ Any other available operations? Read, write, compare etc.? $\endgroup$ – Evil Oct 10 '16 at 4:30
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    $\begingroup$ Think about how you would define the factorial function recursively as a mathematical function, then implement that. But "How do I code X in language Y?" is off-topic at Computer Science. $\endgroup$ – David Richerby Oct 10 '16 at 7:54
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we were required to do something similar. We were given a number to calculate, which was 7!.r0 will hold the final value. I ended up doing the following:

MOV r1, #7 MOV r1, #6 MOV r1, #5 MOV r1, #4 MOV r1, #3 MOV r1, #2 MOV r1, #1

MUL r0, r1, r2 MUL r0, r0, r3 MUL r0, r0, r4 MUL r0, r0, r5 MUL r0, r0, r6 MUL r0, r0, r7

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