# \[heapsort\] Protect against integer overflow · gitcafe/zig

[View on GitCafe](https://git.cafe/gitcafe/zig/commit/7d511d642845c860ec212b9ee39e371d3f70a68b)

Repository: [gitcafe/zig](https://git.cafe/gitcafe/zig)

Visibility: public

Requested revision: 7d511d642845c860ec212b9ee39e371d3f70a68b

Requested commit: 7d511d642845c860ec212b9ee39e371d3f70a68b

Commit: 7d511d642845c860ec212b9ee39e371d3f70a68b

Tree: e4e58d563eaff0c35b1b56a734914d0761b5e1d2

Author: Niles Salter

Committer: GitHub

## Message

```
[heapsort] Protect against integer overflow

(Firstly, I changed `n` to `b`, as that is less confusing. It's not a length, it's a right boundary.)

The invariant maintained is `cur < b`. In the worst case `2*cur + 1` results in a maximum of `2b`. Since `2b` is not guaranteed to be lower than `maxInt`, we have to add one overflow check to `siftDown` to make sure we avoid undefined behavior.

LLVM also seems to have a nicer time compiling this version of the function. It is about 2x faster in my tests (I think LLVM was stumped by the `child += @intFromBool` line), and adding/removing the overflow check has a negligible performance difference on my machine. Of course, we could check `2b <= maxInt` in the parent function, and dispatch to a version of the function without the overflow check in the common case, but that probably is not worth the code size just to eliminate a single instruction.
```

## Parents

- [c60896743d3b0776a44ac63582f51b6e64892528](https://git.cafe/gitcafe/zig/commit/c60896743d3b0776a44ac63582f51b6e64892528?format=markdown)

[Source at this commit](https://git.cafe/gitcafe/zig/tree/7d511d642845c860ec212b9ee39e371d3f70a68b?format=markdown)