• Adam S (7/7) Feb 14 2014 I seem to be having some difficulty with the nan and init
• Adam D. Ruppe (5/6) Feb 14 2014 nan never equals nan, this is in the floating point spec used by
• bearophile (5/6) Feb 14 2014 Additionally, the init NaN doesn't have the same bitpattern as
• Jonathan M Davis (9/14) Feb 15 2014 To be more precise, NaN is never equal to _anything_ - not even itself. ...

"Adam S" <longestpants gmail.com> writes:

I seem to be having some difficulty with the nan and init 
properties of floating point types. Can anyone explain why the 
following assertions all fail:

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

Thanks.

"Adam D. Ruppe" <destructionator gmail.com> writes:

On Saturday, 15 February 2014 at 05:18:51 UTC, Adam S wrote:
 assert(float.init == float.nan);

nan never equals nan, this is in the floating point spec used by 
D, C and others.

Use this instead:
http://dlang.org/phobos/std_math.html#isNaN

"bearophile" <bearophileHUGS lycos.com> writes:

Adam D. Ruppe:

 nan never equals nan,

Additionally, the init NaN doesn't have the same bitpattern as 
the other. There are many NaNs.

Bye,
bearophile

Jonathan M Davis <jmdavisProg gmx.com> writes:

On Saturday, February 15, 2014 05:28:05 Adam D. Ruppe wrote:
 On Saturday, 15 February 2014 at 05:18:51 UTC, Adam S wrote:
 assert(float.init == float.nan);

 
 nan never equals nan, this is in the floating point spec used by
 D, C and others.

To be more precise, NaN is never equal to _anything_ - not even itself. Any 
comparison with NaN as one of the operands results in false - just like any 
floating point arithmetic with NaN in it results in NaN. The idea is that that 
way the error which introduced NaN in the first place will propagate and 
therefore be found rather than being hidden. Sometimes, this is very useful, 
and sometimes it's a bit annoying, but it's way the IEEE floating point spec 
says that it's supposed to be.

- Jonathan M Davis