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Comment by kstrauser | Hacker News Reader

Ohhh, so it'd be kind of like the SQL

  (NULL < 0 || NULL == 0 || NULL > 0)

where even though it seems like one of those would have to be true, yet all 3 are individually unknown? Got it. Thanks for the explanation!

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My knowledge of SQL NULL is rusty, but I think NULL is just plain unordered with respect to other values, more akin to a NaN value in floating-point than an indeterminate value.

Yeah, the details are a little different, but I think the concept's similar. Is null < 0? Uh, not sure. Is it equal to zero? No clue. Is it greater than 0? Can't tell. So, are any of those true? No way of knowing.

  SQLite-3.54 in-memory-> select NULL < 0 or NULL == 0 or NULL > 0;
  ╭──────────────────────╮
  │ NULL < 0 or NULL ... │
  ╞══════════════════════╡
  │ NULL                 │
  ╰──────────────────────╯

It's not the same. Maybe `NaN != NaN` (I don't know SQL enough to tell if `NULL != NULL`), but it can't be true that you observe `NaN == NaN` and then `!(NaN == NaN)`. With LLVM's `undef` this is entirely possible.

Though all of this explanation is only in LLVM IR level. In C, this is just UB and it is also possible that this will erase your hard drive.

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