Solution to inaccurate floating point calculation comparison and rounding in PHP_PHP Tutorial

Solution to inaccurate floating point calculation comparison and rounding in PHP

Comparison of floating point calculation results
An example of floating point calculation is as follows:

The code is as follows:

$a = 0.2 0.7;
$b = 0.9;
var_dump($a == $b);

The printed result is: bool(false). In other words, the calculation result of 0.2 0.7 here is not equal to 0.9, which is obviously against our common sense.

Regarding this issue, the official PHP manual once stated: Apparently a simple decimal fraction such as 0.2 cannot be converted to an internal binary format without losing a little precision. This has to do with the fact that it is impossible to express certain decimal fractions exactly with a finite number of digits. For example, 1/3 in decimal becomes 0.3333333….

We print the above variables in double precision format:

The code is as follows:

$a = 0.2 0.7;
$b = 0.9;
printf("%0.20f", $a);
echo '
';
printf("%0.20f", $b);

The output results are as follows:

The code is as follows:

0.89999999999999991118
0.90000000000000002220

Obviously here, as floating-point data, part of its accuracy has been lost and cannot be completely accurate. So never trust that a floating-point number result is accurate to the last digit, and never compare two floating-point numbers for equality. It should be noted that this is not a problem with PHP, but a problem with the computer's internal processing of floating point numbers! The same problem will be encountered in languages ​​such as C and JAVA.

So to compare two floating point numbers, we need to control them within the precision range we need before comparing, so use the bcadd() function to add the floating point numbers and convert the precision (to a string):

The code is as follows:

var_dump(bcadd(0.2,0.7,1) == 0.9); // Output: bool(true)

Floating point number rounding

In the article "PHP rounding functions ceil and floor", there is an example:

The code is as follows:

echo ceil(2.1/0.7); // Output: 4
?>

After the above discussion on floating-point number calculations, we know that this is caused by the inaccurate floating-point number calculation results:

The code is as follows:

printf("%0.20f", (2.1/0.7)); // Output: 3.00000000000000044409
?>

After the above discussion on floating-point number calculations, we know that this is caused by the inaccurate floating-point number calculation results, so we can use the round() function to deal with it:

The code is as follows:

echo ceil( round((2.1/0.7),1) );
?>

Although the round() function rounds according to the specified precision, retaining one decimal place has no effect on our rounding result.

http://www.bkjia.com/PHPjc/971921.htmlwww.bkjia.comtruehttp: //www.bkjia.com/PHPjc/971921.htmlTechArticleComparison of floating point number calculations in PHP and solutions to inaccurate rounding The example is as follows: The code is as follows: $a = 0.2 0.7; $b = 0.9; var_dump($a == $...