Incorrect result of Fibonacci Number

[studyeveryday7]

Describe the bug

In the Fibonacci Number module, when input a negative number like -6, the output is incorrect.

Expected behavior

I expected the result should be not negative. Maybe change the input negative number to positive number can solve it, and add a dialog to show the reason.

To reproduce

1. Open NCalc+ (Which is build from latest source code)
2. Go to Fibonacci Number module
3. Input -6
4. Click the evaluate bottom
5. Incorrect result has been displayed

Configuration

• Android version 9
• device MI 8 Lite

Screenshots

[danger-ahead]

Hi can you please assign me? I can fix it

[studyeveryday7]

Hi can you please assign me? I can fix it

sure！thank you

[danger-ahead]

@axkr I have created a pull request with the fix.
Thanks!

[axkr]

Sorry for not looking earlier, but I think the negative result is OK:

• https://www.wolframalpha.com/input/?i=fibonnaci%28-6%29

[hakanai]

-8 is indeed the correct answer, assuming the standard positioning of the sequence with Fib(0) = 0:

• Fib(-6) = -8
• Fib(-5) = 5
• Fib(-4) = -3
• Fib(-3) = 2
• Fib(-2) = -1
• Fib(-1) = 1
• Fib(0) = 0
• Fib(1) = 1
• Fib(2) = 1
• Fib(3) = 2
• Fib(4) = 3

The reporter possibly was off by one or something as every second value is indeed not negative.