Origin of Quake3's Fast InvSqrt()

geo writes: "Beyond3D.com's Ryszard Sommefeldt dons his seersucker hunting jacket and meerschaum pipe to take on his secret identity as graphics code sleuth extraordinaire. In today's thrilling installment, the origins of one of the more famous snippets of graphics code in recent years is under the microscope — Quake3's Fast InvSqrt(), which has been known to cause strong geeks to go wobbly in the knees while contemplating its simple beauty and power. Enter the puzzle palace here."