Editing Quake III Arena (section)

===Fast inverse square root===
{{Main|Fast inverse square root}}
Fast inverse square root, sometimes referred to as Fast InvSqrt() or by the [[hexadecimal]] constant 0x5F3759DF, is an algorithm that estimates <math>\frac{1}{\sqrt{x}}</math>, the [[Multiplicative inverse|reciprocal]] (or multiplicative inverse) of the [[square root]] of a 32-bit [[floating-point]] number <math>x</math> in [[Single-precision floating-point format#IEEE 754 single-precision binary floating-point format: binary32|IEEE 754 floating-point format]]{{Broken anchor|date=2024-12-28|bot=User:Cewbot/log/20201008/configuration|target_link=Single-precision floating-point format#IEEE 754 single-precision binary floating-point format: binary32|reason= The anchor (IEEE 754 single-precision binary floating-point format: binary32) [[Special:Diff/1079572738|has been deleted]].}}. The algorithm is best known for its implementation in the source code of ''Quake III Arena.''

At the time, it was generally [[computationally expensive]] to compute the reciprocal of a floating-point number, especially on a large scale. However, the fast inverse square root bypassed this step.

Around 2002, initial speculation pointed to John Carmack as the probable author of the code, but he demurred and suggested it was written by Terje Mathisen, an accomplished assembly programmer who had previously helped id Software with ''Quake'' optimization. Mathisen had written an implementation of a similar bit of code in the late 1990s, but the original authors proved to be much further back in the history of 3D computer graphics with Gary Tarolli's implementation for the [[SGI Indigo]] as a possible earliest known use.