RE: [SDK]Double to long in c++ ?

["Kim Aldis" <XSI(at)kim-aldis.co.uk>]

You sure?

 

(long)t*3*nPoints casts t then multiplies by 3 then nbPoints.

(long)(t*3*nPoints) is ambiguous because the compiler has to work out what you want – t int or 3/nPoints float).

 

I’d take the former, it’s completely un-ambiguous.

 

From: owner-xsi(at)Softimage.COM [mailto:owner-xsi(at)Softimage.COM] On Behalf Of Mathieu Leclaire
Sent: 07 June 2007 18:49
To: XSI(at)Softimage.COM
Subject: RE: [SDK]Double to long in c++ ?

 

Wow, my emails really don’t seam to pass through. I’ve been trying to send this reply since yesterday. Let me try one more time…

 

Here’s what I believe is happening:

 

You have a space between (long) and t. So I believe doing long id = (long) t * 3 * nbPoints; is the equivalent of doing long id = (long)(t * 3 * nbPoints); I think this way it converts the result of the entire equation so if t = 1.99, then you get something like 23.88 and then cast it to a long so it'll only keep the 23. But if you remove the space it’ll do the equivalent of long id = (long)(t) * 3 * nbPoints; but if you have 1.99 and cast it to a long, it'll only keep the value 1 which will screw up the result even more. So you can use round(t) and that'll convert a 1.5 to a 2 and a 1.49 to 1. 

 

But I still find it weird that when you log it, it only shows the value 2 even if the real value would be 1.99. But try those and let me know if it helps.

 

I think round is in Math.h so you might need to include that library.

 

 

Mathieu Leclaire

R&D Programmer

Hybride Technologies

 

"Yesterday is history, tomorrow is a mystery, today is a gift and that is why it's called the present"

 

-----Original Message-----
From: Luc-Eric Rousseau [mailto:lucer(at)Softimage.COM]
Sent: Thursday, June 07, 2007 1:14 PM
To: XSI(at)Softimage.COM
Subject: RE: [SDK]Double to long in c++ ?

 

I perfer to use 0.25, because if you're rendering in fields in XSI the time will be 1.0, 1.5, 2.0,

2.5.  but in fact any small espilon number is fine

 

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From: owner-xsi(at)Softimage.COM [mailto:owner-xsi(at)Softimage.COM] On Behalf Of Kim Aldis
Posted At: Thursday, June 07, 2007 1:07 PM
Posted To: xsi
Conversation: [SDK]Double to long in c++ ?
Subject: RE: [SDK]Double to long in c++ ?

Shouldn’t that be 0.5, not 0.25?

 

From: owner-xsi(at)Softimage.COM [mailto:owner-xsi(at)Softimage.COM] On Behalf Of Luc-Eric Rousseau
Sent: 07 June 2007 02:10
To: XSI(at)Softimage.COM
Subject: RE: [SDK]Double to long in c++ ?

 

these additionnal casts are not necessary because the entire _expression_ is being promoted to 'double' already, and you do need my +0.25 epsilon to control the truncation that hapens with the cast to 'long'

 

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From: owner-xsi(at)Softimage.COM [mailto:owner-xsi(at)Softimage.COM] On Behalf Of Wessam Al-Bahnasi
Posted At: Thursday, June 07, 2007 12:03 AM
Posted To: xsi
Conversation: [SDK]Double to long in c++ ?
Subject: RE: [SDK]Double to long in c++ ?

Or better yet:

 

double t = (double)T + (double)oOffset;
long id = (long)(t * 3.0 * (double)nbPoints);

 

Wessam Bahnassi

Microsoft DirectX MVP,

Programmer

Electronic Arts

--

'Talk is cheap because supply exceeds demand'

 

From: owner-xsi(at)Softimage.COM [mailto:owner-xsi(at)Softimage.COM] On Behalf Of Luc-Eric Rousseau
Sent: Wednesday, June 06, 2007 3:31 PM
To: XSI(at)Softimage.COM
Subject: RE: [SDK]Double to long in c++ ?

 

I don't really know the answer to your question, so I appologize if this is wrong, but the cast operator has higher precedence than the multiply. so it's going to take that 't', cast it to a long, and do the rest in longs.

I think you wanted to have another set of parenthesis like (long)(t*3*nbPoints)

 

in any case,

casting a double to long just like that is not a good idea, you should add an epsilon to compensate for any numerical innacuracies.

For example  :  long id = (long)(t*3*nbPoints + 0.25);

 

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From: owner-xsi(at)Softimage.COM [mailto:owner-xsi(at)Softimage.COM] On Behalf Of Ahmidou Lyazidi
Posted At: Wednesday, June 06, 2007 3:20 PM
Posted To: xsi
Conversation: [SDK]Double to long in c++ ?
Subject: [SDK]Double to long in c++ ?

Hi
In an Operator,we are trying to convert the datas passed by OperatorContex.GetTime to a long.The thing that is strange is when I log the value
it seems good, but when I mutiply it with a fixed value it seems to round it and give me 2 equal values for 2 differant frame
here is the code and the log:

long oOffset = oOp.GetParameterValue(L"TimeOffset");

CTime T = ctxt.GetTime();
Application().LogMessage(L"Current operator Time " + T.GetAsText());

double t = double(T) + oOffset;
long id = (long) t * 3 * nbPoints;