Fast inverse square root, sometimes called Fast InvSqrt or referred to by its hexadecimal constant 0x5F3759DF, is an algorithm that estimates the reciprocal of the square root of a 32-bit floating-point number in IEEE 754 format. It is best known for its implementation in the 1999 game Quake III Arena, and it works by treating the bits of the input as an integer, performing a logical right shift, and subtracting the result from the constant to produce an initial guess that is then refined with one iteration of Newton's method.
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