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PHP floating point calculation problem
- 巴扎黑Original
- 2016-11-22 11:06:581577browse
If you use PHP's +-*/ to calculate floating point numbers, you may encounter some problems with incorrect calculation results. For example, echo intval(0.58*100); will print 57 instead of 58. This is actually due to the inability of the underlying binary system of the computer. A bug in accurately representing floating point numbers
is cross-language. I also encountered this problem using python. So basically most languages provide class libraries or function libraries for precise calculations. For example, PHP has a BC high-precision function library. Here are some commonly used BC high-precision functions.
php BC high-precision function library includes: addition, comparison, division, subtraction, remainder, multiplication, nth power, configure the default number of decimal points, and square. These functions are more useful when it comes to monetary calculations, such as e-commerce price calculations.
/**
* Compare two high-precision numbers
*
* @access global
* @param float $left
* @param float $right
* @param int $scale The number of decimal places to be accurate
*
* @return int $left==$right returns 0 | $left<$right returns -1 | $left>$right returns 1
*/
var_dump(bccomp($left=4.45, $right=5.54, 2));
// -1
/**
* Add two high-precision numbers
*
* @access global
* @param float $left
* @param float $right
* @param int $scale The number of decimal places to be accurate
*
* @return string
*/
var_dump(bcadd($left=1.0321456, $right=0.0243456, 2));
//1.04
/**
* Subtract two high-precision numbers
*
* @access global
* @param float $left
* @param float $right
* @param int $scale The number of decimal places to be accurate
*
* @return string
*/
var_dump(bcsub($left=1.0321456, $right=3.0123456, 2));
//-1.98
/**
* Divide two high-precision numbers
*
* @access global
* @param float $left
* @param float $right
* @param int $scale The number of decimal places to be accurate
*
* @return string
*/
var_dump(bcdiv($left=6, $right=5, 2));
/ /1.20
/**
* Multiply two high-precision numbers
*
* @access global
* @param float $left
* @param float $right
* @param int $scale The number of decimal places to be accurate
*
* @return string
*/
var_dump(bcmul($left=3.1415926, $right=2.4569874566, 2));
//7.71
/**
* Set the number of decimal points for the bc function
*
* @access global
* @param int $scale The number of decimal points to be accurate
*
* @return void
* /
bcscale(3);
var_dump(bcdiv('105', '6.55957'));
// 16.007
Note: Regarding the number of digits set, the excess is discarded, not Rounding