NaN() and if compare problem

[mk-soft]

ASM and C-backend test ...

Code: Select all

Define.d Number, Number2 = 1.2

; ASM OK, C-Backend Bug?
Number = Sqr(-1)
If Number = NaN()
  Debug "If / Ok: Number = NaN()"
Else
  Debug "Else / Bug: Number = NaN()"
EndIf

; ASM OK, C-backend Ok
Number = Sqr(-1)
If IsNAN(Number)
  Debug "If / Ok: IsNaN(Number)"
Else
  Debug "Else / Bug: IsNaN(Number)"
EndIf

; ASM Bug, C-Backend Bug
Number2 = 1.2
If Number = Number2
  Debug "If / Bug: Number = Number2"
Else
  Debug "Else / Ok: Number = Number2"
EndIf

[Little John]

Code: Select all

; ASM OK, C-Backend Bug?
Number = Sqr(-1)
If Number = NaN()
[...]

Wrong code. In order to check for NaN, only use PB's IsNaN() function.

NaN is a special value. Testing for it should not be done using normal comparisons because there are actually many different values for NaN and whether or not NaN is considered equal with itself in comparisons depends on the hardware.

[juergenkulow]

Wiki: NaN=x false

[DarkDragon]

The inequality of NaN against NaN is the early version of the IsNaN check. So if x <> x it is NaN. But it should be the same on all backends.