Comment by AlotOfReading

5 days ago

I'm pretty sure it's not faster, but it was fun to write:

    float asin(float x) {
      float x2 = 1.0f-fabs(x);
      u32 i = bitcast(x2);
      i = 0x5f3759df - (i>>1);
      float inv = bitcast(i);
      return copysign(pi/2-pi/2*(x2*inv),x);
    }

Courtesy of evil floating point bithacks.

8 comments

AlotOfReading

Reply
teo_zero  5 days ago

The bad thing about this method is that it's slower than native CPU instructions. The good thing is that the result is very precise for at least 2 values of x, namely 1.0 and -1.0

JK

  • AlotOfReading  4 days ago

    Yeah, it's an interesting approximation. It follows the shape of the curve pretty well except around 0, much better than low degree polynomials. Polynomial approximations have much better relative error bounds though.