alt Hacker NewsReally? It's been done plenty and I thought was quite common knowledge. Some of the <stdbit.h> provided functions are basically for this purpose.
stdc_bit_ceil(len) gets the smallest power of 2 not less than len, which is our capacity. This is usually implemented with a clz instruction.
stdc_has_single_bit(len) determines if it's a power of 2 - typically implemented with a popcount instruction (popcount(len)==1).
The approach isn't used in older (90s and earlier) texts because hardware support for popcount/clz wasn't commonplace and the cost to do it in software wasn't worth it, but it is mentioned in some texts.
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Everyone knows about bit-fiddling functions, what the poster was referring to is using this trick to not have to store the capacity for a dynamic vector. Which is genuinely very clever and rare, I don’t think I’ve ever seen it done quite like this either. I think that’s probably because it’s not really that good of an idea, if the vector can shrink, you really should store the capacity.
I think it was sarcasm. I have about as much experience as them in low-level C programming, and I was wondering why this is on front page. I've also discovered again a few things too, so I won't look down on OP. It's certainly better than vibe coding.