Nim：如何检查一个浮点数是 nan 还是 inf？

Question

如何检查浮点变量是 NaN 还是 inf。在标准库中搜索 isNaN 或 isInf 不会显示任何内容。有一个 blog post 建议使用

proc cIsNaN(x: float): int {.importc: "isnan", header: "<math.h>".}

但是标准库中真的什么都没有吗？

Answer 1

标准库确实提供了对NaN/inf的检查，但是在classify的广义概念下，这也是容易漏掉的原因。举例说明：

import math

# Inf and NaN literals are defined in system.nim as
# Inf* {.magic: "Inf".} = 1.0 / 0.0
# NaN* {.magic: "NaN".} = 0.0 / 0.0

let floatsToTest = [0.0, Inf, NaN]
for x in floatsToTest:
  echo x, " is NaN ", x.classify == fcNaN
  echo x, " is inf ", x.classify == fcInf

输出：

0.0 is NaN false
0.0 is inf false
inf is NaN false
inf is inf true
nan is NaN true
nan is inf false

classify 还可以测试其他属性，例如 fcSubnormal、fcNegZero 或 fcNegInf（参见 FloatClass）。

Answer 2

您可以添加自己的功能

import std/math

func is_number*(n: float): bool =
  let ntype = n.classify
  ntype == fc_normal or ntype == fc_zero or ntype == fc_neg_zero

Nim：如何检查一个浮点数是 nan 还是 inf？

Nim: How to check if a float is nan or inf?

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