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digitalmars.D.bugs - [Issue 8562] New: math.pow fails at compile-time

reply d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=8562

           Summary: math.pow fails at compile-time
           Product: D
           Version: D2
          Platform: x86_64
        OS/Version: Linux
            Status: NEW
          Severity: major
          Priority: P2
         Component: Phobos
        AssignedTo: nobody puremagic.com
        ReportedBy: iteronvexor gmail.com



template T(){
  enum a = pow(3.0, 6);
  enum b = pow(2, 4.0);
}

unittest
{
  alias T!() t;
}

compiling that I get:

/home/b/phobos/std/math.d(2369): Error: Cannot convert &real to ushort* at
compile time
/home/b/phobos/std/math.d(3292):        called from here: isNaN(y)
/home/b/phobos/std/math.d(3403):        called from here: impl(x,cast(real)y)
/home/b/phobos/std/math.d(3239):        called from here: pow(cast(real)x,y)
t.d(478):        called from here: pow(2,4)
t.d(485): Error: template instance units.T!() error instantiating


I guess technically it's math.isNaN() that's failing?

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next sibling parent d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=8562




yup, it's math.isNaN().

template T() {
  enum a = isNaN(1.3);
}

unittest
{
  alias T!() t;
}

/home/b/phobos/std/math.d(2369): Error: Cannot convert &real to ushort* at
compile time
t.d(474):        called from here: isNaN(1.3L)
t.d(479): Error: template instance units.T!() error instantiating


God please, will somebody fix this?

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Aug 19 2012
prev sibling next sibling parent d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=8562


Don <clugdbug yahoo.com.au> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |clugdbug yahoo.com.au



isNan(x) can be implemented at compile time by:

return (x != x);

It's not exactly the same at run time, because it sets the floating point
hardware exception flags, whereas isNaN does not. But there are no exception
flags at compile time.

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prev sibling next sibling parent d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=8562






 isNan(x) can be implemented at compile time by:
 
 return (x != x);
 
 It's not exactly the same at run time, because it sets the floating point
 hardware exception flags, whereas isNaN does not. But there are no exception
 flags at compile time.


To avoid the casting in isNaN() you would need to know when it's getting called
at compile-time and when it's getting called at run-time, correct?  There is no
way to know that, so we end up with two functions, isNaN() and staticIsNaN(),
correct?

bool staticIsNaN(R)(R x) if(isFloatingPoint!R)
{
  return x != x;
}

p.s.
why are exception flags being set in a nothrow?

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prev sibling next sibling parent d-bugmail puremagic.com writes:
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Jonathan M Davis <jmdavisProg gmx.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |jmdavisProg gmx.com



PDT ---

 To avoid the casting in isNaN() you would need to know when it's getting
called at compile-time and when it's getting called at run-time, correct? 
There is no way to know that, so we end up with two functions, isNaN() and
staticIsNaN(), correct?


Wrong. __ctfe is true during CTFE and not during runtime. So, you can do

if(__ctfe)
{
    //ctfe version
}
else
{
    //normal version
}

http://dlang.org/function.html#interpretation

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prev sibling next sibling parent d-bugmail puremagic.com writes:
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great, I didn't know about __ctfe.

Now isInfinity() is failing at compile time because of the same reasons as
isNaN().  How do you check to see if a floating point is infinity at compile?

return x == real.infinity

???

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prev sibling parent d-bugmail puremagic.com writes:
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ok, so pow() calls exp2(), which contains tons of asm statements, which means
pow() can't be executed at compile time.

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