POV-Ray : Newsgroups : povray.binaries.scene-files : U equals zero - or not : Re: U equals zero - or not Server Time
18 Jun 2021 02:54:24 EDT (-0400)
  Re: U equals zero - or not  
From: clipka
Date: 15 Sep 2018 21:13:10
Message: <5b9dae26$1@news.povray.org>
Am 16.09.2018 um 02:36 schrieb Bald Eagle:

> I had added them all, to see why you somehow were able to have the comparison
> evaluate successfully, and have the code execute without error, and then I
> commented out two of them and cycled through, thus narrowing the problem down to
> why #local U = 0; "fixes" the issue.

Huh? I thought the problem was that some variation of "0*N <= 0" didn't
seem to work out; now you're saying that "U=0" wasn't holding?

But the output you posted from the `#debug concat ("Testing Y = ...`
statement clearly showed that at least the debug output accessed the
expected element of UArray, so why should the subsequent `#if` statement
access a different element of UArray, if they both access element [U]?

> This happens in 3.7.0.msvc10.win64, Mr. Balaska's current QTPOV-Ray version,
> (both on the same laptop, dual-boot) and the (IIRC) 32-bit 3.7.0 version on the
> tower at work.

I presume that comma after "3.7.0.msvc10.win64" stands for "and", not
further qualification; i.e. it happens in official POV-Ray for Windows
as well as in QtPOV-Ray.

That pretty much rules out the tenth level of floating point hell
hypothesis, because the official POV-Ray for Windows binaries use
"proper" floating point math.

It also means that we both /should/ get exactly the same results,
because official version 3.7.0.msvc10.win64 is precisely the versions
I've just verified my results with the code you posted prior to posting
my most recent replies.

So the `#if` clause MUST be entered in the first loop iteration (which
/should/ be, and /is/, U=0, with UArray[U]=<0,0,1.047something) -
because that's what is to be expected, and that's what I am absolutely
positively seeing here, double-checked and all, with the exact same
piece of software - unless your CPU is buggy, or some gremlin has pooped
on your RAM, or whatever.

> Attached are scene, includes, and a developmental model of the function for the
> CURVE section at the end of the main scene file.

Sounds like not a minimal scene.
Is it any more enlightening than the code you posted earlier?

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