F#-如何比较浮点数 [英] F# - How to compare floats

问题描述

在F#中.如何有效地比较浮点数是否相等?它也应该适用于非常大和非常小的值.我正在考虑先比较指数，然后比较有效位数(Mantissa)，而忽略其52位中的最后4位.那是一个好方法吗?如何获得浮点数的指数和有效位数?

In F#. How to efficiently compare floats for equality that are almost equal? It should work for very large and very small values too. I am thinking of first comparing the Exponent and then the Significand (Mantissa) while ignoring the last 4 bits of the its 52 bits. Is that a good approach? How can I get the Exponent and Significand of a float?

推荐答案

F#float只是System.Double的简写.在这种情况下，您可以使用 BitConverter.DoubleToInt64Bits 有效(和安全！)将F#float值投射"到int64的方法；如John在其评论中所述，这很有用，因为它避免分配byte[].您可以使用一些简单的按位运算从int64中获取指数和有效数.

An F# float is just a shorthand for System.Double. That being the case, you can use the BitConverter.DoubleToInt64Bits method to efficiently (and safely!) "cast" an F# float value to int64; this is useful because it avoids allocating a byte[], as John mentioned in his comment. You can get the exponent and significand from that int64 using some simple bitwise operations.

如John所说，简单检查相对精度可能会更好.对于许多用例，它可能是最快的解决方案，并且足够接近"(例如，检查迭代求解器是否已收敛于解决方案).如果您需要特定于 的精度，请查看NUnit的代码-它具有一些不错的API，可以断言值在期望值的一定百分比或数量之内.

As John said though, you're probably better off with a simple check for relative accuracy. It's likely to be the fastest solution and "close enough" for many use cases (e.g., checking to see if an iterative solver has converged on a solution). If you need a specific amount of accuracy, take a look at NUnit's code -- it has some nice APIs for asserting that values are within a certain percentage or number of ulps of an expected value.

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