PHP十进制计算 [英] PHP Decimal calculations

问题描述

我读到你必须小心使用PHP进行浮点比较和计算。我不是PHP专家，所以我想问问社区什么是在PHP中进行精确的小数计算的最佳方法。

我正在开发一个计时卡应用程序在哪里计算每周输入的所有时间。超过40小时的任何事情都被视为加班。然后，我想根据进入总时间的百分比，将这个加班时间分配给每个时间条目。

示例：

星期一= 10小时

总时间= 50小时

加班时间= 10小时

总时间百分比（0.2）=星期一（10小时）/总时间（50小时）

加班时间分配到星期一（2小时）=总加班时间（10小时）*总时间百分比（0.2）

$ b $ $ p $ b星期一（8小时）=星期一 - 加班时间分配到星期一（2小时）

星期一加班= 2小时

使用整数作为原始条目似乎并不糟糕，但是当我开始使用浮点数并每天有多个时间条目时会发生什么？每次输入将会有一部分时间分配给它，但是我需要确保不要再分配更多的加班时间，然后我也需要确保每天和整个计时卡的总时间与原来的一样进入。我读过比较浮动php是不安全的。我该如何计算呢？此外，最后输入的数字必须舍入到2个小数点（。##）。

解决方案

阅读浮点指南了解为什么您必须小心混合浮点数和小数点的概念（这与PHP完全无关）。

它也有一个用于PHP的作弊表。

I was reading that you have to be careful with floating point comparisons and calculations in PHP. I'm not an expert at PHP so I thought I would ask the community what is the best way to do accurate decimal calculations in PHP.

I'm developing a timecard application where it calculates all the time entered for the week. Anything over 40 hours is considered overtime. I then want to distribute that overtime back across each time entry based on the percentage that entry is of the total time.

Example:

Monday = 10 hours
Total Time = 50 hours
Total Overtime = 10 hours

Percent of Total time (0.2) = Monday (10 hours) / Total Time (50 hours)
Overtime to Allocate to Monday (2 hours) = Total Overtime (10 hours) * Percent of Total Time (0.2)

Now make a new entry for Monday with 2 hours of overtime and subtract 2 hours from original entry.

New Entries:
Monday (8 hours) = Monday - Overtime to Allocate to Monday (2 hours)
Monday Overtime = 2 hours

Things don't seem to bad when using integers as your original entries but what will happen when I start using floats and have multiple time entries per day? Each time entry will have part of the total overtime allocated to it but I need to make sure not to allocate more overtime then is available and I also need to make sure the total time for each day and for the whole timecard is the same as originally entered. I read comparing floats in php are not safe. How should I do the calculation. Also, the final entered numbers have to be rounded to 2 decimal points (.##)

解决方案

Read The Floating-Point Guide to understand why exactly you have to be careful with mixing floating-point numbers and the concept of "decimals" (which has absolutely nothing to do with PHP specifically).

It also has a cheat-sheet for PHP.

这篇关于PHP十进制计算的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！