Why Are My PHP Floating-Point Calculations Inaccurate?

Floating-Point Imprecision in PHP

Encountering unexpected results when performing floating-point arithmetic in PHP? This issue arises due to the inherent nature of floating-point representation in computers.

Floating-point numbers are binary numbers with limited precision, leading to discrepancies between mathematical expectations and actual results. This means that, unlike real number arithmetic, floating-point arithmetic may encounter inaccuracies such as (a b)-b != a for certain values.

To illustrate, consider the PHP code:

$a = '35';
$b = '-34.99';
echo ($a + $b);

The output is 0.009999999999998, while one would expect 0.01. This deviation occurs because both 34.99 and 0.01 cannot be precisely represented in binary. Instead, approximations are used.

To mitigate this issue, several approaches can be employed:

• Round the result using round($result, 2) to achieve the desired number of decimal places.
• Utilize integers instead of floats. If working with currencies, store values in cents (e.g., $35.00 as 3500) and divide the result by 100.

While PHP lacks a decimal datatype, round function and integer manipulation techniques provide effective workarounds for handling floating-point imprecision.

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