Precautions and tips for comparing PHP floating point numbers

As a commonly used server-side scripting language, PHP often involves comparison operations of floating point numbers. However, due to the precision of floating point numbers, improper use can easily lead to unexpected comparison results. In this article, we will discuss the precautions and techniques for PHP floating point number comparison, and provide specific code examples for readers' reference.

First of all, it is worth noting that floating point numbers are represented in binary within the computer and are not exact decimal numbers. This results in errors that may occur when comparing floating point numbers. The following are some common precautions and techniques:

Notes:

1. Do not directly compare whether floating point numbers are equal

Due to the accuracy of floating point numbers, directly use " ==" to compare two floating point numbers for equality is unreliable. A smaller error margin should be used to judge whether they are close enough.

2. Avoid performing multiple floating-point number operations

Every time you perform a floating-point number operation, errors will accumulate, so the number of multiple floating-point number operations should be minimized.

3. Try to avoid using floating point numbers for loop calculations

Due to accuracy issues, using floating point numbers for loop calculations may lead to inaccurate results.

Tips:

1. Use the bcadd() function to perform floating-point addition operations

The bcadd function is a function provided in PHP for high-precision calculations, which can reduce Floating point arithmetic errors.

$num1 = '1.1';
$num2 = '2.2';
$sum = bcadd($num1, $num2, 1);
echo $sum; // 输出3.3

2. Use the bcmul() function to perform floating-point number multiplication

The bcmul function is also one of the functions used for high-precision calculations, which can reduce floating-point calculation errors.

$num1 = '0.1';
$num2 = '0.2';
$product = bcmul($num1, $num2, 1);
echo $product; // 输出0.02

3. Convert floating point numbers to integers for comparison

Multiply the floating point numbers by a large enough integer multiple, and then convert the results to integers for comparison, which can reduce the number of floating point number comparisons. error.

$num1 = 1.1;
$num2 = 1.2;
$multiplier = 1000;
if ((int)($num1 * $multiplier) == (int)($num2 * $multiplier)) {
    echo "相等";
} else {
    echo "不相等";
}

In summary, although there are certain difficulties in floating-point number comparison in PHP, by observing the precautions and applying skills, we can effectively reduce the errors caused by floating-point number comparison and improve comparison. accuracy. When we need to compare floating point numbers when developing PHP programs, we must pay attention to the above precautions and techniques to avoid errors caused by accuracy issues.

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