The rust code for rounding down is given as let new_ptr = new_ptr & !(align - 1)... | Hacker News

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		asalahli on Sept 19, 2023 \| parent \| context \| favorite \| on: Always Bump Downwards (2019) The rust code for rounding down is given as `let new_ptr = new_ptr & !(align - 1);` But I don't see rdx decremented before being negated and AND'ed with rax, in the assembly. What am I missing?

conradludgate on Sept 20, 2023 [–]

It's being converted into `-align` which is equivalent under twos compliment

asalahli on Sept 20, 2023 | [–]

I don't follow. Are you saying `new_ptr & -align` is equivalent to `new_ptr & !(align - 1)`?

Edit: I get it now. My brain was interpreting NEG as NOT for some reason.

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