On Tuesday, 23 January 2024 at 17:54:25 UTC, bachmeier wrote:
Here's a reduced version of one of the most bizarre bugs I've
dealt with in any language. The only reason I didn't move on to
another language was because I was too busy at the time.
The code allows for initial values if the index is less than 0,
otherwise it returns the element.
```
import std;
double value(T)(T index, double * x) {
if (index - 5 < 0) {
return 0.0;
} else {
return x[index-5];
}
}
void main() {
double[] v = [1.1, 2.2, 3.3];
// Works
writeln(value(3, v.ptr));
// Lucky: program segfaults
writeln(value(v.length, v.ptr));
}
```
I noticed this behavior only because the program crashes. Once
I figured out what was going on, I realized that the thousands
of lines of code I had already written needed to be checked and
possibly rewritten. If only I had a compiler to do that for me.
How did you make it correct?
Write 2 different versions for `signed` and `unsigned` types?
Or could you utilize `core.checkedint` somehow for checking
overflow?
```d
double value(T)(T index, double * x) {
bool overflow;
subu(index, 5, overflow);
if (overflow) {
return 0.0;
} else {
return x[index-5];
}
}
```
This is probably only correct for `unsigned` types.
