使用PHP处理大量数字 [英] Working with large numbers in PHP

问题描述

要使用

To use modular exponentiation as you would require when using the Fermat Primality Test with large numbers (100,000+), it calls for some very large calculations.

当我将两个大数相乘(例如:62574和62574)时，PHP似乎将结果转换为浮点数.获取那个的模量值会返回奇怪的值.

When I multiply two large numbers (eg: 62574 and 62574) PHP seems to cast the result to a float. Getting the modulus value of that returns strange values.

$x = 62574 * 62574;
var_dump($x);          // float(3915505476) ... correct
var_dump($x % 104659); // int(-72945)  ... wtf.

有什么方法可以使PHP正确执行这些计算?另外，还有另一种方法可以找到适用于大数的模量值吗?

Is there any way to make PHP perform these calculations properly? Alternatively, is there another method for finding modulus values that would work for large numbers?

推荐答案

由于某种原因，PHP中有两个标准库可以处理任意长度/精度数字: GMP .我个人更喜欢GMP，因为它更新鲜且具有更丰富的API.

For some reason, there are two standard libraries in PHP handling the arbitrary length/precision numbers: BC Math and GMP. I personally prefer GMP, as it's fresher and has richer API.

基于GMP，我已经实现了 Decimal2类，用于存储和处理货币金额(例如100.25美元).那里的很多 mod计算没有任何问题.经过很多大量测试.

Based on GMP I've implemented Decimal2 class for storing and processing currency amounts (like USD 100.25). A lot of mod calculations there w/o any problems. Tested with very large numbers.

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