OpenEuphoria

RE: Uninitialized Variables

• Posted by Andy Serpa <renegade at earthling.net> Mar 23, 2002
• 426 views

If this message comes through twice, I'm sorry -- the web interface is 
very slow today:

Ok, here's the test so we don't get tricked by the optimizer:
equal(anything,copy of anything) will always be true -- you have to make 
a nan that isn't just a copy of your definition.

-------------------
atom x,y,nan,inf, z, unknown
inf = 1e300 * 1e300
nan = -(inf / inf) -- ( inf / inf = -nan )

x = 10         -- not a nan
y = -tan(inf)  -- a nan
z = nan        -- a different nan
----------------------------

Now, assume you don't know what x,y, & z are.  Show me a way to identify 
the nans & non-nans, AND continues to work when translated to C (except 
with Borland -- all of these big number things crash Borland).

THIS works in all cases I know of:
------------------------------------
unknown = x

if unknown and compare(unknown/unknown,1) then
	puts(1,"NAN!\n")
else
	puts(1,"non-NAN!\n")
end if

unknown = y

if unknown and compare(unknown/unknown,1) then
	puts(1,"NAN!\n")
else
	puts(1,"non-NAN!\n")
end if

unknown = z

if unknown and compare(unknown/unknown,1) then
	puts(1,"NAN!\n")
else
	puts(1,"non-NAN!\n")
end if


---------------

This works in the interpreter, but not when compiled:

unknown = x

if unknown = 1 and unknown = 2 then
	puts(1,"NAN!\n")
else
	puts(1,"non-NAN!\n")
end if
-----------------


As I said, using atom_to_float32() also would work it seems, but you 
have to account for nan & -nan.


So one way involves two comparisons & a division; the other involves 
converting to a sequence & then up to two comparisions.  Isn't there a 
cheaper way?