找到一个给定数量的使用按位运算的平方根 [英] Finding the square root of a given number using bitwise operations

问题描述

有一个算法使用位运算找到一个定数的平方根？

Is there an algorithm to find the square root of a given number using bitwise operations?

推荐答案

有这个著名的一块$的C $Ç魔术的，计算的逆的平方根有一些非常聪明的位操作。它错误地归功于约翰·卡马克 - 这里有一个更深层次的挖掘到它的起源。也许这就是你问的？

There is this famous piece of code magic that computes inverse square root with a some very clever bit twiddling. It is wrongfully attributed to John Carmack - here's a deeper dig into its origin. Maybe that's what you're asking about?

我不建议使用它，但。在现代的CPU是不能战胜专用超然的说明。你通常的C ++内在的sqrt（）很可能会战胜它手了。

I wouldn't suggest using it, though. On modern CPU's it cannot beat dedicated transcendental instructions. Your usual c++ intrinsic sqrt() would probably beat it hands down.

所引用的文章描述了一个通用的推导方法，这种快速的逼近，并明确指出推导的sqrt（x）的类似的方法作为其最终线一门功课的问题。所以，你应该能够直接跟踪其推理和制定一个类似的方法开方（不倒数）。

The cited article describes a general derivation method for such fast approximations, and explicitly states 'Derive a similar method for sqrt(x)' as a homework problem at its final lines. So you should be able to track its reasoning and devise a similar method for sqrt (without the reciprocal) directly.

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