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Christoffer Lernö
3 hours, 36 minutes ago
Last post about arithmetics I listed the following problems related to overflow and arithmetics:
  1. Overflow traps on unsigned integers makes the mixed signedness case very hard to get right.
  2. Overflow traps cause unexpected and hard-to-spot non commutative and associative behaviour in expressions that otherwise would have been fine.
  3. Wrapping behaviour enables buffer overflows and similar exploits.
  4. In most languages it doesn't matter if the left hand sign can contain the number, what matters are the types on the right hand side, which isn't always intuitive or desired.

Let's look at some attempts to fix these problems, starting with handling mixed ... Read More →


Christoffer Lernö
3 days, 6 hours ago
It is generally understood that overflowing an add or a multiplication is usually a bad thing. This seems to imply that the solution is to detect and trap (quit the program or throw an exception) on such errors. But as we will see, the answer isn't that clear cut.

Commutative and associative addition?


Typically when we work with integers, we prefer that the ordering of the operands doesn't matter. For example, if we see a + b + c we'd prefer that (a + b) + c is the same as a + (b + c).

Unfortunately, if we ... Read More →


Christoffer Lernö
3 days, 6 hours ago
The defer statement is going mainstream. Go has it's own special defer which only fires on function end, otherwise defer has consistent "execute at scope end" semantics. Swift, Zig, Jai, Nim and Odin all use defer in this manner.

The problems with implementing defer is similar to implementing destructors for stack allocated objects in C++, although the presence of virtual functions complicates things.

I couldn't find anyone describing how defer is done in other compilers so when working on a version of it for C2 I had to make it up as I went along.

For posterity's sake I ... Read More →