Posted by francisco.j.garau on Feb 22, 2008; 1:14pm
URL: https://forum.world.st/vwnc-Floats-and-NaNs-tp1410164.html

Hi,

On a windows image runnig VW 7.5, trying to print a NaN causes infinite
recursion, and eventually crashes the image.

bytes := #[ 255 255 255 255].
nanFloat := Float basicNew.
bytes doWithIndex: [:b :i | nanFloat basicAt: i put: b].

nanFloat printString
=> causes infinite recursion as #printOn:digits: calls #negated which in
turn tries to do an arithmetic operation on a NaN. As the primitive fails,
the double dispatch takes on and #abs is called on the NaN which in turns
calls #negated again.

Debug It
Float>>differenceFromFloat:
Float>>-
Float(ArithmeticValue)>>negated
Float(ArithmeticValue)>>abs
Float>>differenceFromFloat:
Float>>-
Float(ArithmeticValue)>>negated
Float(LimitedPrecisionReal)>>printOn:digits:
Float(LimitedPrecisionReal)>>printOn:
Float(Object)>>printString

My proposed fix is as follows:

Number >> isNaN
        ^false

Float >> isNaN
        ^self exponent = 128

Double >> isNaN
        ^self exponent = 1024

LimitedPrecissionReal >> printOn: aStream digits: digits
        self > 0.0 ifTrue:
                [^self absPrintOn: aStream digits: digits].
        self = 0.0 ifTrue:
                [aStream nextPutAll: '0.0'.
                ^self class == Float ifFalse: [aStream nextPut: self class
exponentCharacter]].
        self isNaN ifTrue:
                [^aStream nextPutAll: 'NaN'].
        self < 0.0 ifTrue:
                [aStream nextPutAll: '-'.
                ^self negated absPrintOn: aStream digits: digits].
        self error: 'mysterious number'





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