PHP floating point accuracy problem

Source: Internet
Author: User
Tags modulus square root

This period of time to maintain a similar group purchase system, the need to process orders, it will inevitably deal with the amount of PHP is a lot of the pit was my hard stepping on ~ ~

First we need to know the representation of floating-point numbers (IEEE 754):

In short, you bury a pit and wait for you to jump. For example, when handling floating-point addition and subtraction

<? PHP Echo (53.55-(3.67+49.88)); // -7.105427357601E-15?>

There is wood feel deeply malicious, but also PHP according to standard execution can only be circuitous forward;


Bcmath Arbitrary Precision Mathematics

    • BC Math Functions
      • Bcadd-add arbitrary precision numbers
      • Bccomp-compare arbitrary precision numbers
      • Bcdiv-divide arbitrary precision numbers
      • Bcmod-get modulus of an arbitrary precision number
      • bcmul-multiply arbitrary Precision Number
      • Bcpow-raise an arbitrary precision number to another
      • Bcpowmod-raise an arbitrary precision number to another, reduced by a specified modulus
      • Bcscale-set Default scale parameter for all BC math functions
      • Bcsqrt-get the square root of an arbitrary precision number
      • Bcsub-subtract one arbitrary precision number from another

It's also very simple to use, for example

<? PHP // Echo (53.55-(3.67+49.88)); Echo (floatval(bcsub(bcadd(3.67,49.88), 53.55));

Although-0 but also the effect of processing achieved,


PHP floating point accuracy problem

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