issue 7006 - std.math.pow (integral, integral) crashes on negative exponents

[Timon Gehr]

On 15.12.19 19:22, berni44 wrote:
> A few hours ago I closed issue 7006 [1] as a WONTFIX. Now 
> timon.gehr at gmx.ch opened it again, without any explanation.

You didn't provide an explanation for closing the issue, so I assumed it 
was an accident. -1^^-1 leading to "division by zero" instead of the 
correct answer of -1 makes no sense at all.

> As I don't 
> wont to start an edit war, I prefere to get some other opinions from the 
> community.
> 
> It's about the integer overload of pow() in std.math and the issue askes 
> for adding support for negative exponents. IMHO there are two 
> possibilites and non of them makes sense to me:
> 
> a) Result type integral: There is no usecase,

Nonsense, e.g., (-1)^^i.

> because in almost all 
> cases the result is a fraction which cannot be expressed as an integral 
> type. Even when looking at this as a division with reminder, the value 
> would always almost be 0. Again not very useful.
> 
> b) Result type floating: This would be a breaking change. If the user 
> wishes this behaviour he could convert the base to a floating type first 
> and then call pow. Additionally it occasionally would produce wrong 
> results as I pointed out in my closing message.
> ...

This is not an option.

> What do you think about this?
> 
> [1] https://issues.dlang.org/show_bug.cgi?id=7006

A negative exponent should behave like a negative exponent. I.e., a^^-1 
= 1/a. There's no good reason to do anything else.