fmod不正确吗?

本文介绍了fmod不正确吗?的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！ 问题描述

给出以下双打， fmod 返回正确的值吗?

Given the following doubles, does fmod return the correct value?

double x = .090; double y = .003; double r = fmod(x, y); // r = 0.0029999999999999949

为什么r = 0?

推荐答案

由于与大多数小数部分一样，这些数字不能用二进制浮点格式精确表示.要查看实际使用的值:

Because, like most decimal fractions, these numbers can't be represented exactly by a binary floating point format. To see what values are actually being used:

#include <cstdio> int main() { printf("%.20f %.20f\n", .090, .003); } Output: 0.08999999999999999667 0.00300000000000000006

这些小的舍入误差意味着第一个值略小于第二个值的精确倍数，因此您可以看到结果.

These small rounding errors mean that the first value is slightly less than an exact multiple of the second, hence the result you see.

您可能希望允许较小的错误容忍度:

You may want to allow a small tolerance for error:

if (r > y - some_small_value) { r = 0; }