Fast Inverse Square Root — A Quake III Algorithm

In this video we will take an in depth look at the fast inverse square root and see where the mysterious number 0x5f3759df comes from. This algorithm became famous after id Software open sourced the engine for Quake III. On the way we will also learn about floating point numbers and newton’s method. 0:00 Introduction 1:23 Why Care? 3:21 The Code 4:18 IEEE 754 9:38 Bits and Numbers 12:09 1st Step: Evil Bit Hack 14:46 2nd Step: WTF 17:34 3rd Step: Newton 19:46 Summary Picture of John Carmack is licensed under CC BY 2.0 from author Drew “Prognar“ Campbell. Source: