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Comment by umanwizard

5 hours ago

Signed overflow being UB (while unsigned is defined to wrap) is a quirk of C and C++ specifically, not some fundamental property of computing.

5 comments

umanwizard

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xigoi  4 hours ago

Nim (the original one, not Nimony) compiles to C, so making basic types work differently from C would involve major performance costs.

  • ratmice  4 hours ago

    Presumably unsigned want to return errors too?

    Edit: I guess they could get rid of a few numbers... Anyhow it isn't a philosophy that is going to get me to consider nimony for anything.

  • umanwizard  4 hours ago

    > making basic types work differently from C would involve major performance costs.

    Not if you compile with optimizations on. This C code:

      int wrapping_add_ints(int x, int y) {
      return (int)((unsigned)x + (unsigned)y);
  }

    Compiles to this x86-64 assembly (with clang -O2):

      wrapping_add_ints:
          lea     eax, [rdi + rsi]
          ret

    Which, for those who aren't familiar with x86 assembly, is just the normal instruction for adding two numbers with wrapping semantics.

Symmetry  4 hours ago

Specifically, C comes form a world where allowing for machines that didn't use 2's compliment (or 8 bit bytes) was an active concern.

  • aw1621107  3 hours ago

    Interestingly, C23 and C++20 standardized 2's complement representation for signed integers but kept UB on signed overflow.