Fast face normals
Post: #17Quote:Originally posted by kainsinWell put.
Math rules.
"He who breaks a thing to find out what it is, has left the path of wisdom."
- Gandalf the Gray-Hat
Bring Alistair Cooke's America to DVD!
Post: #18
BTW, a friend of mine realized this just now:
(1/sqrt(x))*x = sqrt(x)
DOY!
so to summarize:
(1/sqrt(x))*x = sqrt(x)
DOY!
so to summarize:
Code:
static const float gOneHalf = 0.5;
// calculate 1/sqrt(x) with pretty good accuacy
// x is double to prevent frsp generation before call
// return type is float to prevent frsp generation after call
float asm fastSqrtRecip(register double x) {
frsqrte fp2,x; // inv = 1/sqrt(x)
lfs fp3,gOneHalf(RTOC);
fmuls x,x,fp2; // f*inv
fres x,x; // 1/(f*inv)
fadds x,x,fp2; // 1/(f*inv)+inv
fmuls x,x,fp3; // .5*(1/(f*inv)+inv)
blr;
}
// calculate sqrt(x) with pretty good accuacy
// x is double to prevent frsp generation before call
// return type is float to prevent frsp generation after call
float asm fastSqrt(register double x) {
frsqrte fp2,x; // inv = 1/sqrt(x) // inv = 1/sqrt(x)
lfs fp3,gOneHalf(RTOC); // load 0.5
fmuls x,x,fp2; // f*inv
fres fp2,fp2; // 1/inv
fadds x,x,fp2; // 1/inv+f*inv
fmuls x,x,fp3; // .5*(1/inv+f*inv)
blr;
}"He who breaks a thing to find out what it is, has left the path of wisdom."
- Gandalf the Gray-Hat
Bring Alistair Cooke's America to DVD!
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