Warnings about the precision of floating-point numbers in PHP

Source: Internet
Author: User
Warning for floating point accuracy in PHP

This is a hint from PHP document:

A simple decimal score like 0.1 or 0.7 cannot be converted to an internal binary format without losing a little bit of precision.

Floor ((0.1 + 0.7) *)? return 7 instead of 8,

(int) ((0.1 + 0.7) * 10)? Returns 7 instead of 8.


The explanation for this phenomenon is "because the internal representation of the result is actually similar to 7.9".


So the result is:

So never believe that the floating-point number is accurate to the last one, and never compare two floating-point numbers for equality.

Never cast an unknown fraction to an int.


(int) Round (0.1 + 0.7) * 10) This seems to be safe.

The BC math function is used for numerical accuracy when there is a large number of multiplication or if the median value is float type.


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