I do like teaching with chalk. I don’t like this so much.
Stephen Checkoway
@stevecheckoway.bsky.social
479 followers 455 following 856 posts
Associate Professor of Computer Science at Oberlin College. No kings, no nazis, no war.
Associate Professor of Computer Science at Oberlin College. No kings, no nazis, no war.
![Screenshot of bsky’s Chat settings page. It reads,
We’re sorry, you cannot access this screen at this time.
Due to laws in your region [which apply to porn sites and not to social media], certain features on Bluesky are currently restricted until you’re able to verify you’re an adult.](https://cdn.bsky.app/img/feed_thumbnail/plain/did:plc:4e3pymuwv3j5ni7oryqk2t2k/bafkreiekrvttfr5xvkdl3rqxnffcludvm2367ldadgzhrfolufxq2jmvly)
![Screenshot of a slide: Integer overflow checking in C is difficult
On the left, a C function int safe_add(int a, int b) checks if a > 0 && b > 0 and if so, then if a + b <= 0, abort(). Otherwise, if a < 0 && b < 0, then if a + b >= 0, abort(). Otherwise return a + b.
On the right, the x86-64 assembly code produced by gcc. It's two instructions long:
safe_add:
lea eax, [rdi + rsi]
ret
It is adding a and b and returning the result.
The overflow checks have been optimized away. You know, for efficiency. The compiler produced no indication that it had done this.](https://cdn.bsky.app/img/feed_thumbnail/plain/did:plc:4e3pymuwv3j5ni7oryqk2t2k/bafkreih6ox5kp7bkqz3qeohw4knzuef7kg5eyxdohcca5ymlgayfatkb74)