Let’s talk about common problems in floating point number conversion in PHP

Floating point numbers play a very important role in programming, including economic calculations, data recording, physical simulation and other fields. However, some problems may arise when it comes to floating-point calculations due to the computer's storage and processing mechanisms. This article will introduce floating point number conversion, precision issues, solutions and best practices in PHP.

1. Representation of floating-point numbers

In computers, floating-point numbers are composed of a decimal and an exponent, and are usually represented by scientific notation.

For example: 1.234e 4 means 1.234 times 10 raised to the fourth power. This number is divided into two parts:

• Coefficient: 1.234
• Exponent: 4

In PHP, floating point numbers It is expressed in 64-bit format IEEE-754 and has the following components:

1. Sign bit: The first bit represents positive and negative, 0 is a positive number, and 1 is a negative number.
2. Exponent bit: The middle 11 bits represent the exponent, using the exponent code representation method. The value range is -1022 ~ 1023, which is offset by 1023, so the value in the encoding is the actual value 1023.
3. Mantissa bits: The remaining 52 bits represent the mantissa, using binary decimal notation.

2. Floating point number conversion problem in PHP

1. An error occurs when performing simple floating point operations

In PHP, there is no problem in performing simple addition, subtraction, multiplication, and division operations on floating point numbers, but when performing complex calculations, errors can easily occur.

For example:

$a = 0.1;
$b = 0.2;
$c = $a + $b;
echo $c; //0.3
if ($c == 0.3) {
    echo 'true';
} else {
    echo 'false';
}

When executing this code, the result output is false. This is because the way floating point numbers are stored in the computer is different from the decimal representation, and there is an accuracy problem.

2. Failure to convert floating point number to string

When converting floating point number to string, conversion failure may also occur.

For example:

$val = 0.0000005;
$str = (string)$val;
echo $str; //5.0E-7

This string is obviously not converted in the way we expected. This is because floating point numbers use scientific notation, so they are also expressed in scientific notation when converted to strings.

3. Floating point conversion solutions and best practices in PHP

1. Use comparison operators for comparison

In When comparing floating point numbers, we should not use the equality operator (==) directly, but can use the following solution:

$a = 0.1;
$b = 0.2;
$c = $a + $b;
$epsilon = 0.00001;//可以酌情调整
if(abs($c - 0.3) < $epsilon) {
    echo 'true';
} else {
    echo 'false';
}

Here we set an error range $epsilon, when the absolute value of the calculated result is the expected When the difference between the results is less than $epsilon, the two numbers are judged to be equal.

2. Use sprintf function to format output

When we need to convert floating point numbers into strings, we can use sprintf function to format output.

For example:

$val = 0.0000005;
$str = sprintf("%.10f", $val);
echo $str; //0.0000005000

%.10f in the sprintf function means outputting 10 digits after the decimal point. The original meaning of %f is "floating point number", plus the number 10 following the decimal point. , indicates the number of decimal points to be retained in floating point numbers.

3. Use the BC math function library

If you need high-precision calculations, you can use the BC math function library. This library provides functions that support high-precision data operations, which can avoid precision errors in floating-point calculations.

For example:

$a = '0.1';
$b = '0.2';
$c = bcadd($a, $b, 3);
echo $c; //0.300

This method requires the BC math function library to be explicitly introduced in the code, and it also needs to be called according to the specifications of the library function when used.

4. Summary

Through this article, we have learned about the common problems and solutions that may occur when converting floating point numbers in PHP. Although there are accuracy problems in PHP's underlying floating-point calculations, we can solve these problems through some techniques and library functions to provide more reliable numerical calculation support for project implementation.

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