sin() / cos() speed

Strayfire · 2004-05-30T02:32:33

I'm reading Tricks of the 3D Game Programming Gurus at the moment, and LaMothe writes that the trig functions are very slow and that the best thing to do when comuting sin and cos in a game is to use pre-built lookup tables. This is obviously faster, but in this book he creates a function that calculates sin and cos for non-integer values. I performed a small speed test and it turns out that calculating these values from the lookup table was actually *slower*! For your game engines, do you guys just use the sin() and cos() functions, or is there a better way? By the way, the code from the book is something like this: float Sin(float theta) { theta = fmodf(theta,360); if(theta < 0) theta += 360; int iThetaInt = (int)theta; float fThetaFrac = theta - iThetaInt; return(fSin[iThetaInt] + fThetaFrac * (fSin[iThetaInt + 1] - fSin[iThetaInt])); } Turns out that the fmodf() function seems to take twice as long as just calling sin()! [edited by - Strayfire on May 29, 2004 12:27:27 AM]

For Beginners

Started by Strayfire May 29, 2004 11:26 PM

10 comments, last by Strayfire 19 years, 10 months ago

Strayfire

162

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May 30, 2004 02:26 AM

Well, the last few functions on changing the precision haven''t worked for me (fatal errors) but the inline Sin() function is working fine for me. Can''t say I really understand what''s going in the precision code. I know a fair bit of assembly language, but not much when it comes to floating point numbers. I ordered and received the intel IA-32 manuals and AMD64 manuals about 4 months ago, but still haven''t gotten around to reading them. Thanks a bunch for the code and reminding me that I still had those manuals lying around

-----------My Counter-Strike is broken!

temp_ie_cant_thinkof_name

100

May 30, 2004 02:32 AM

Glad to help. Which functions weren''t working? The ones in my last post, the macros? B/c they should work... I may not have the syntax down though. Anyway, I just thought it would be nice to know that the FPU was working with single precision instead of extended-double, which is 2x slower (guesstamating). I don''t know if VC++ sets the Precision Control field in the FPU Control Word or not, so that''s why i''m curious.

"I study differential and integral calculus in my spare time." -- Karl Marx

sin() / cos() speed

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sin() / cos() speed

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