• Acarion <asdfa asf .com> Oct 07 2007
• BCS <ao pathlink.com> Oct 07 2007
• Daniel Keep <daniel.keep.lists gmail.com> Oct 07 2007
• Nathan Reed <nathaniel.reed gmail.com> Oct 07 2007
• Sean Kelly <sean f4.ca> Oct 07 2007
• "Janice Caron" <caron800 googlemail.com> Oct 07 2007

Acarion <asdfa asf .com> writes:

I have this code:

float number=getFloat();
assert(number!=float.nan); //this passes
assert(to!(char[])(number)!="nan"); //this fails
writefln(string.toString(number)); //this outputs: "nan"
writefln( to!(char[])(to!(long)(number)) ); //this generates an error

What did I do wrong?

BCS <ao pathlink.com> writes:

Reply to acarion,

 I have this code:
 
 float number=getFloat();
 assert(number!=float.nan); //this passes


IIRC this will also pass:

assert(float.nan != float.nan);

this is because D used IEEE floating point semantics. Under IEEE a comparison 
with NaN will always be  not equal

If you want to test for nan use "testedValue !<>= 0"* or the isnan function

 assert(to!(char[])(number)!="nan"); //this fails
 writefln(string.toString(number)); //this outputs: "nan"
 writefln( to!(char[])(to!(long)(number)) ); //this generates an error
 What did I do wrong?
 


* this is the not grater than, less than, or equal to operator.

Daniel Keep <daniel.keep.lists gmail.com> writes:

BCS wrote:
 Reply to acarion,
 
 I have this code:

 float number=getFloat();
 assert(number!=float.nan); //this passes


 IIRC this will also pass:
 
 assert(float.nan != float.nan);
 
 this is because D used IEEE floating point semantics. Under IEEE a
 comparison with NaN will always be  not equal
 
 If you want to test for nan use "testedValue !<>= 0"* or the isnan function


You can also use (x!=x) to test to see if x is NaN, and (x==x) to make
sure it is not NaN.

	-- Daniel

Nathan Reed <nathaniel.reed gmail.com> writes:

Janice Caron wrote:
 On 10/7/07, BCS <ao pathlink.com> wrote:
 If you want to test for nan use "testedValue !<>= 0"


 Are we really sure about that?
 
 If testedValue is complex (with non-zero real part) then it will not
 be less than 0, it will not be greater than zero, and it will not be
 equal to zero. But it will also not be NaN.


I believe you'd get a type error in that case (real and creal can't be 
directly compared, etc.)  Haven't tried it though.

Thanks,
Nathan Reed

Sean Kelly <sean f4.ca> writes:

BCS wrote:
 Reply to acarion,
 
 I have this code:

 float number=getFloat();
 assert(number!=float.nan); //this passes


 IIRC this will also pass:
 
 assert(float.nan != float.nan);
 
 this is because D used IEEE floating point semantics. Under IEEE a 
 comparison with NaN will always be  not equal
 
 If you want to test for nan use "testedValue !<>= 0"* or the isnan function


I tend to use:

testedValue !<>= testedValue

Though I've occasionally wondered whether the 'is' identity operator 
should work for checking against nan:

testedValue is float.nan



Sean

"Janice Caron" <caron800 googlemail.com> writes:

On 10/7/07, BCS <ao pathlink.com> wrote:
 If you want to test for nan use "testedValue !<>= 0"


Are we really sure about that?

If testedValue is complex (with non-zero real part) then it will not
be less than 0, it will not be greater than zero, and it will not be
equal to zero. But it will also not be NaN.