Why 0.5+0.2+0.2+0.1 is not equal to 1 when PHP is doing addition calculation

$sum=(0.5+0.2+0.2+0.1);//var_dump   float(1)$sum2=1  //var_dump   int(1)$sum == $sum2  //var_dump  bool(false)

What's the matter, please?
In addition, the following tests are possible.
For example

（0.5+0.2+0.3+0.0)==1  //var_dump  bool(true)

Reply content:

$sum=(0.5+0.2+0.2+0.1);//var_dump   float(1)$sum2=1  //var_dump   int(1)$sum == $sum2  //var_dump  bool(false)

What's the matter, please?
In addition, the following tests are possible.
For example

（0.5+0.2+0.3+0.0)==1  //var_dump  bool(true)

When calculating numbers, use Bcmath (point me to point me)

phpvar_dump(bcadd(0.1+0.001));var_dump(0.1+0.001);

The method of binary representation of decimal in the computer results in inaccurate accuracy
All the languages are like this decimal is more commonly used
ABS (expression) < 1e-14 (or other than very small number)

One is a float point, one is an integer, as for the following to understand the PHP source code in depth

This is the problem of floating point accuracy, which exists in all languages and is explained in the PHP Documentation: link Address

The classic question depends on the explanation of the great God.
Http://www.laruence.com/2013/03/26/2884.html

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