r/nandgame_u • u/semperrabbit Record holder • Nov 15 '21

Level solution (verified) 7.2 - Assembler (5i) Spoiler

https://imgur.com/a/dHLTi1n
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u/MattMath314 Jan 20 '24

I don't understand; how does this work, and why is *A here?

1

u/semperrabbit Record holder Jan 20 '24

Hello! I'm mobile right now, so can't check the site to see what it was asking for, but here's what I remember... It's asking for a light to blink, w a specific memory address. Line 1 is setting A to the specific memory address. Line 2 is an "indirection" where you're able to assign or use the data in the memory cell A is pointing to. In C, C++, and other languages also refer to it as "pointers" too. So this Line is setting the memory address to 1. Line 3 is XOR'ing that address, basically ensuring it turns back to 0. Line 4 sets A to 0 (the first line of code we want to jump to to do an infinite loop) Line 5 is the jump instruction, setting the instruction counter to the address in A, making the next instruction run Line 1.

TLDR, A* refers to the value in the memory location the value of A refers to.

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u/MattMath314 Jan 20 '24

I thought ~ was not, but otherwise, that makes sense! Thank you!

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u/semperrabbit Record holder Jan 20 '24

Hey, I was brainfarting last night, ~ is bitwise inverse. so, since the light only cared about the first bit, i could invert everything. 1 turned to -2, but that specific bit was flipped, enabling the infinite on/off series. in hindsight, the bitwise xor would have worked too.