alt Hacker NewsIs there a specific reason to store the key + value as an `uint64_t` instead of just using a struct like this?
struct slot {
uint32_t key;
uint32_t value;
}Replies
zimpenfish • yesterday at 4:48 PM
Maybe trying to avoid struct padding? Although having done a quick test on {arm64, amd64} {gcc, clang}, they all give the same `sizeof` for a struct with 2x`uint32_t`, a struct with a single `uint64_t`, or a bare `uint64_t`.
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loeg • yesterday at 7:26 PM
No real reason. Slightly terser to compare with zero to find an empty slot.
mwkaufma • yesterday at 10:09 PM
Or better, just store keys and values in separate arrays, so you can have compact cache lines of just keys when probing.
The alignment constraint is different, which they use to be able to load both as a 64-bit integer and compare to 0 (the empty slot).
You could work around that with a union or casts with explicit alignment constraints, but this is the shortest way to express that.