Fast calculation of inverse square root with the use of magic constant – analytical approach

摘要

We present a mathematical analysis of transformations used in fast calculation of inverse square root for single-precision floating-point numbers. Optimal values of the so called magic constants are derived in a systematic way, minimizing either relative or absolute errors. We show that the value of the magic constant can depend on the number of Newton–Raphson iterations. We present results for one and two iterations.