Instead of using glRotate() for a camera I was thinking of constructing sin and cos tables and using that.
I was looking at old gaming making tutorials and they say such tables speed up the code. Does that still hold today? Or is it that it doesnt matter with todays faster CPUs?
do your table
I suggest you go for the functions, not look up tables. CPU's are fast enough.
Anyways, if performance matters, this is one of the last places you should care about. Algorithmic optimization (choose the right way instead of doing the wrong way as fast as possible) is WAY more efficient
>>I was looking at old gaming making tutorials<<
the key word here is 'old' since the pentium even the 486 this is not an isse in fact it will be slower when youre using them with glRotatef(..)
the only place where they would improve performance is if youre calculating 1000's of sin/cos in a very tight inner loop.
but even with this ild still go with cos/sin + not the tables ie the next cpu might do sos/cos's in 1 cycle
I acutally tried that. I had some kind of coarse sine/cosine lookup table (128 entries) and did a linear interpolation between two entries. I though something like "Hey, that's only one kilobyte, should be nice on the caches. There's no way FSINCOS can be faster.". Of course FSINCOS was faster than this 'optimization'. And more precise to boot.
(On my old system, Athlon 'Classic' 600, 100MHz el cheapo SDRAM).
Just out of interest - can someone tell me what is wrong with the following item?
Cheers!
inline void sincos ( float Ang, float& Sin, float &Cos )
{
__asm {
fld Ang
fsincos
fstp Cos
fstp Sin
}
}
Zed,
The only thing wrong with you logic, is that I do not see any CPU in the next few decades making a sine or cosine call run in 1 cycle. The faster the CPU just runs the same number of cycles faster nothing more. If a CPU could spit out an answer for sine or cosine in 1 cycle that would imply that the CPU circuitry would have sine and cosine logic added on the chip itself. However, if that happens it may take several cycles due to sine and cosine are too complicated functions. As far as I know, multiplication is not even directly encoded on the chip. It is just a bunch of additions... that is why adding is faster than multiplying.
I cannot tell you why there is a problem but I can verify that there is a problem with it ...Originally posted by Robbo:
Just out of interest - can someone tell me what is wrong with the following item?
Cheers!
inline void sincos ( float Ang, float& Sin, float &Cos )
{
__asm {
fld Ang
fsincos
fstp Cos
fstp Sin
}
}
And the output is ...Code :#include <iostream> using namespace std; inline void sincos ( float Ang, float& Sin, float &Cos ) { __asm { fld Ang fsincos fstp Cos fstp Sin } } #define PI 3.141592654 #define DEG_TO_RAD PI/180.0f void main() { float dAng,fAng; float fSin,fCos; for (dAng=0.0f; dAng<360.0f; dAng += 5.0f) { fAng = dAng*DEG_TO_RAD; sincos(fAng,fSin,fCos); cerr << dAng << ", " << fSin << ", " << fCos << endl; } }
Code :0, 5.88346e-039, 5.88387e-039 5, 5.88346e-039, 5.88387e-039 10, 5.88346e-039, 5.88387e-039 15, 5.88346e-039, 5.88387e-039 20, 5.88346e-039, 5.88387e-039 25, 5.88346e-039, 5.88387e-039 30, 5.88346e-039, 5.88387e-039 35, 5.88346e-039, 5.88387e-039 40, 5.88346e-039, 5.88387e-039 45, 5.88346e-039, 5.88387e-039 50, 5.88346e-039, 5.88387e-039 55, 5.88346e-039, 5.88387e-039 60, 5.88346e-039, 5.88387e-039 65, 5.88346e-039, 5.88387e-039 70, 5.88346e-039, 5.88387e-039 75, 5.88346e-039, 5.88387e-039 80, 5.88346e-039, 5.88387e-039 85, 5.88346e-039, 5.88387e-039 90, 5.88346e-039, 5.88387e-039 95, 5.88346e-039, 5.88387e-039 100, 5.88346e-039, 5.88387e-039 105, 5.88346e-039, 5.88387e-039 110, 5.88346e-039, 5.88387e-039 115, 5.88346e-039, 5.88387e-039 120, 5.88346e-039, 5.88387e-039 125, 5.88346e-039, 5.88387e-039 130, 5.88346e-039, 5.88387e-039 135, 5.88346e-039, 5.88387e-039 140, 5.88346e-039, 5.88387e-039 145, 5.88346e-039, 5.88387e-039 150, 5.88346e-039, 5.88387e-039 155, 5.88346e-039, 5.88387e-039 160, 5.88346e-039, 5.88387e-039 165, 5.88346e-039, 5.88387e-039 170, 5.88346e-039, 5.88387e-039 175, 5.88346e-039, 5.88387e-039 180, 5.88346e-039, 5.88387e-039 185, 5.88346e-039, 5.88387e-039 190, 5.88346e-039, 5.88387e-039 195, 5.88346e-039, 5.88387e-039 200, 5.88346e-039, 5.88387e-039 205, 5.88346e-039, 5.88387e-039 210, 5.88346e-039, 5.88387e-039 215, 5.88346e-039, 5.88387e-039 220, 5.88346e-039, 5.88387e-039 225, 5.88346e-039, 5.88387e-039 230, 5.88346e-039, 5.88387e-039 235, 5.88346e-039, 5.88387e-039 240, 5.88346e-039, 5.88387e-039 245, 5.88346e-039, 5.88387e-039 250, 5.88346e-039, 5.88387e-039 255, 5.88346e-039, 5.88387e-039 260, 5.88346e-039, 5.88387e-039 265, 5.88346e-039, 5.88387e-039 270, 5.88346e-039, 5.88387e-039 275, 5.88346e-039, 5.88387e-039 280, 5.88346e-039, 5.88387e-039 285, 5.88346e-039, 5.88387e-039 290, 5.88346e-039, 5.88387e-039 295, 5.88346e-039, 5.88387e-039 300, 5.88346e-039, 5.88387e-039 305, 5.88346e-039, 5.88387e-039 310, 5.88346e-039, 5.88387e-039 315, 5.88346e-039, 5.88387e-039 320, 5.88346e-039, 5.88387e-039 325, 5.88346e-039, 5.88387e-039 330, 5.88346e-039, 5.88387e-039 335, 5.88346e-039, 5.88387e-039 340, 5.88346e-039, 5.88387e-039 345, 5.88346e-039, 5.88387e-039 350, 5.88346e-039, 5.88387e-039 355, 5.88346e-039, 5.88387e-039
Obsessive - A word used by the lazy to describe the motivated.
Cos and Sin in this function are pointers. You need some dereferencing.Originally posted by Robbo:
Just out of interest - can someone tell me what is wrong with the following item?
Cheers!
inline void sincos ( float Ang, float& Sin, float &Cos )
{
__asm {
fld Ang
fsincos
fstp Cos
fstp Sin
}
}
Do something likeCheers.Code :fld Ang fsincos MOV ESI,Cos MOV EDI,Sin fstp [ESI] fstp [EDI]
Bear in mind that FSINCOS expects the angle in radians not in degrees.
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