POV-Ray : Newsgroups : povray.advanced-users : Testing for NaNs Server Time
24 Nov 2024 21:46:37 EST (-0500)
  Testing for NaNs (Message 1 to 4 of 4)  
From: David Wallace
Subject: Testing for NaNs
Date: 10 Jan 2005 03:54:08
Message: <41e242b0@news.povray.org>
I've been running into errors with one of my supersurface tests:

<code>
// Parametric variable form

#declare uMin = 0; // Minimum u value
#declare uMax = radians(180); // Maximum u value
#declare uNum = 90; // Number of points in u direction
#declare uWrap = 0; // u wraps around if != 0
#declare uSeed = 2252; // Random number seed for u parameter

#declare vMin = 0; // Minimum v value
#declare vMax = radians(356); // Maximum v value
#declare vNum = 90; // Number of points in v direction
#declare vWrap = 1; // v wraps around if != 0
#declare vSeed = 7335; // Random number seed for v parameter

#declare IsRnd = false; // True if random number used
#declare IsUV = true; // True if uv-mapping used
#declare Smooth = 1; // Smooth flag

#declare Detail = "Partial"
/* Detail values
  Verbose = Line by line details
  Partial = Operations only
  Other = Filename only
*/

/* For all macro functions
 i = Current value of u parameter
 j = Current value of v parameter
 p = Current value of u variance (0...1)
 q = Current value of v variance (0...1)
*/

// Optional functions

#macro rd(a,b,m,n1,n2,n3,th)
 #local ra = abs(cos(m*th*0.25)/a);
 #local rb = abs(sin(m*th*0.25)/b);
 pow(pow(ra,n2)+pow(rb,n3),-1/n1)
#end

#macro pof(n,ex,of) pow((n+of)*(n+of),ex*.5)-of #end

#declare a1=pi+2;
#declare b1=pi-2;
#declare m1=5.5;
#declare n11=1.50;
#declare n21=1.75;
#declare n31=1.25;

#declare a2=phi(2);
#declare b2=phi(3);
#declare m2=1;
#declare n12=0.30;
#declare n22=-.25;
#declare n32=-.35;

// point function
#macro pnt(i, j, p, q)
 #local rdi = rd(a1,b1,m1,n11,n21,n31,i+1e-3); // altered
 #local rdj = rd(a2,b2,m2,n12,n22,n32,j+1e-3);
 #local si = sin(i);
 #local ci = cos(i);
 #local sj = sin(j);
 #local cj = cos(j);

  /*torus
  #local xp = sj*(rdj+rdi*si);
  #local yp = cj*(rdj+rdi*si);*/
  //sphere
  #local xp = rdj*cj*rdi*si;
  #local yp = rdj*sj*rdi*si;
  #local zp = rdi*ci;
  #local dz = pof(zp, 1.3, 4.5);
  <xp+.1*dz,zp,yp>
#end
</code>

Certain values of th, particularly 0, in the rd macro results in a NaN (Not
a Number) from dividing by 0 if n2 or n3 are negative.  A quick, dirty
workaround was the code marked "altered" which ensured that th never hit 0,
pi/2, pi, etc.

I use the code above to generate large mesh2 objects.  The errors were not
being caught until POV-Ray parsed the meshes, usually several minutes.  I
want to catch these errors more quickly and flag them with #error
directives, causing quick failure the instant one of these calculations goes
awry.

So, what is the fastest and easiest way to detect NaN floats and vectors?

-----------------------------
David Wallace
TenArbor Consulting
"Just In Time Cash"
www.tenarbor.com


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From: Warp
Subject: Re: Testing for NaNs
Date: 10 Jan 2005 05:40:24
Message: <41e25b98@news.povray.org>
David Wallace <dar### [at] earthlinknet> wrote:
> So, what is the fastest and easiest way to detect NaN floats and vectors?

  There isn't.

  What happens eg. with a division by 0 is completely system-dependant,
and even whether you get a 'NaN' value or something else is
system-dependant. (In fact, the 'NaN' value itself is system-dependant
because not all architectures implement the IEEE floating point numbers.)
  There's no portable way of testing "is this value a NaN?".

  The only way you can prevent it from happening is to test the
operands of the division prior to performing the division.

-- 
plane{-x+y,-1pigment{bozo color_map{[0rgb x][1rgb x+y]}turbulence 1}}
sphere{0,2pigment{rgbt 1}interior{media{emission 1density{spherical
density_map{[0rgb 0][.5rgb<1,.5>][1rgb 1]}turbulence.9}}}scale
<1,1,3>hollow}text{ttf"timrom""Warp".1,0translate<-1,-.1,2>}//  - Warp -


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From: ABX
Subject: Re: Testing for NaNs
Date: 10 Jan 2005 07:13:32
Message: <3vr4u093dc6ui3erqpalcp8931nn1lmggn@4ax.com>
On 10 Jan 2005 05:40:24 -0500, Warp <war### [at] tagpovrayorg> wrote:
> There's no portable way of testing "is this value a NaN?".

Hmm, IIRC there are already some assumptions about features of the compiler
for POV-Ray and isnan() is part of (C99) standard
http://www.opengroup.org/onlinepubs/009695399/functions/isnan.html

ABX


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From: Tor Olav Kristensen
Subject: Re: Testing for NaNs
Date: 10 Jan 2005 13:16:15
Message: <41e2c66f$1@news.povray.org>
Are you (btw.) aware that it is possible to declare user
defined functions in POV-Ray ?

I think your code can be improved by using some of those.

You can find some relevant source code for POV-Ray here:
http://astronomy.swin.edu.au/~pbourke/povray/supershape/

-- 
Tor Olav
http://subcube.net
http://subcube.com


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