26 ms·

Even for fixnums, integer overflows and underflows of any kind should ideally result in an exception by default. I think it's a pity that C(++) doesn't have sup

Even for fixnums, integer overflows and underflows of any kind should ideally result in an exception by default. I think it's a pity that C(++) doesn't have support for this. A lot of bugs and weaknesses could have been prevented (for example, CWE 680 http://cwe.mitre.org/data/definitions/680.html http://cwe.mitre.org/data/definitions/680.html). I know this decision (to simply wrap around in the case of an over/underflow) was probably performance-driven, but on the other hand, if the common languages had required it, CPUs would have better support for it... Edit: Some googling shows that Microsoft has a SafeInt class in common use that reports under/overflow: http://safeint.codeplex.com/ http://safeint.codeplex.com/ . Still it feels like a kludge for this to be not part of the main language.

JoachimSchipper 15y ago
(Hint: gcc has a -ftrapv option, which traps on signed integer overflow. Unsigned overflow is defined, so trapping on that would break working code.)
- wladimir 15y ago
  I don't think I'd necessarily want to trap on all (signed) integer overflows. As you say, it might break working code. There's just too much C/C++ code around to change that retroactively. And for modular arithmetic and such it is desirable for integers to wrap around. But a "trap on overflow" signed and unsigned int type would be nice.
  - JoachimSchipper 15y ago
    Recent gcc versions use the fact that signed overflow is undefined to do some unexpected optimizations (in particular, a + b < a will never be true if a, b are ints.) I don't think -ftrapv is going to cause many additional errors, but I haven't actually tried it. (Also, http://embed.cs.utah.edu/ioc/ http://embed.cs.utah.edu/ioc/ looks interesting.)
    - Natsu 15y ago
      > (in particular, a + b < a will never be true if a, b are ints.) Code of exactly that form in the patch for this bug made me do a double take. Fortunately, they'd also changed the a & b from plain ints to size_t, so it was ok.

JoachimSchipper 15y ago

(Hint: gcc has a -ftrapv option, which traps on signed integer overflow. Unsigned overflow is defined, so trapping on that would break working code.)

wladimir 15y ago
I don't think I'd necessarily want to trap on all (signed) integer overflows. As you say, it might break working code. There's just too much C/C++ code around to change that retroactively. And for modular arithmetic and such it is desirable for integers to wrap around. But a "trap on overflow" signed and unsigned int type would be nice.
- JoachimSchipper 15y ago
  Recent gcc versions use the fact that signed overflow is undefined to do some unexpected optimizations (in particular, a + b < a will never be true if a, b are ints.) I don't think -ftrapv is going to cause many additional errors, but I haven't actually tried it. (Also, http://embed.cs.utah.edu/ioc/ http://embed.cs.utah.edu/ioc/ looks interesting.)
  - Natsu 15y ago
    > (in particular, a + b < a will never be true if a, b are ints.) Code of exactly that form in the patch for this bug made me do a double take. Fortunately, they'd also changed the a & b from plain ints to size_t, so it was ok.