Created: 22 November 2007 | Watched by: 2 people | Comments: 0 comments

• Add to my
  bookmarks

  Add comment

  1 group
  2 people
  

  CodeMaestro » Magical Square Root Implementation In Quake III 

  http://www.codemaestro.com/reviews/9

  Any 3D engine draws it’s power and speed from the mathematical models and implementations within, and trust John Carmack of ID software for using really good hacks. As it turns out, a very interesting ... hack is used in Quake III to calculate an inverse square root. Preface ID software has recently released the source code of Quake III engine with a GPL license. In this article we’ll see Carmack work his black magic to calculate the square root of a floating point number blazingly fast. Carmack’s Unusual Inverse Square Root A fast glance at the file game/code/q_math.c reveals many interesting performance hacks. The first thing that pops out is the use of the number 0×5f3759df in the function Q_rsqrt, which calculates the inverse square root of a float and why does this function actually work? Observe the original function from q_math.c : float Q_rsqrt( float number ) { long i; float x2, y; const float threehalfs = 1.5F; x2 = number * 0.5F; y = number; i = * ( long * ) &y; // evil flo   [More...] [Less...]

  First added: 22 November 2007, by: David Wiblin  [Report as spam]

  Average rating (2 ratings):

  1 2 3 4 5

  Tags:  software, accuracy, approximation, performance, root , speed up, sqrt, square root   [More...] [Less...]