Reasons for PHP floating point calculation errors

Example: (Recommended learning: PHP video tutorial)

echo intval(0.58*100);//结果为57
echo intval((0.1 + 0.7) * 10);//结果为7

The reason for this is that the computer Some floating-point numbers cannot be accurately represented internally in binary, just like we cannot accurately represent 10/3 in decimal.

The internal representation of floating-point numbers in the computer: IEEE 754. If you don’t understand, look it up yourself Information

You can also refer to this article by Bird Brother: http://www.laruence.com/2013/03/26/2884.html

<?php
echo intval(0.58*100);//57,注意啦
echo &#39;<br/>&#39;;
echo intval(bcmul(0.58, 100));//58
echo &#39;<br/>&#39;;
echo floor(strval(0.58*100));//58
echo &#39;<br/>&#39;;
echo (int)(0.58 * 1000/10);//58
echo &#39;<br/>&#39;;
echo intval((0.1 + 0.7) * 10);//7,注意啦
echo &#39;<br/>&#39;;
echo intval(bcadd("0.1", "0.7",1) * 10);  //8
?>

Let’s look at another example

<?php
if((0.1 + 0.7) == 0.8){
	echo &#39;相等&#39;; 
}else{
	echo &#39;不相等&#39;; //这里输出
}
echo &#39;<br />&#39;;
$a = 0.1 + 0.7;
echo $a; //0.8
echo &#39;<br/>&#39;;
if($a == 0.8){ 
	echo &#39;一天一小步&#39;;
}else{
	echo &#39;一年一大步&#39;; //这里输出
}
echo &#39;<br/>&#39;;
if(strval($a) == 0.8){
	echo &#39;一天一小步&#39;; //这里输出
}else{
	echo &#39;一年一大步&#39;; 
}
echo &#39;<br/>&#39;;
if(bcadd(0.1, 0.7,1) == 0.8){
	echo &#39;一天一小步&#39;; //这里输出
}else{
	echo &#39;一年一大步&#39;;
}
/*
结果:
不相等
0.8
一年一大步
一天一小步
一天一小步
*/
?>

$a = 0.00...00(n zeros)1 0.7; When using strval to obtain the value of $a, the result of whether $a and 0.8 are equal will be caused by the different number of n zeros. Different

The bcadd function will add 2 numbers, depending on how many decimals you choose to keep and discard the following decimals

Look at a division example:

<?php
echo 160500643816367088/10;//1.6050064381637E+16
echo &#39;<br/>&#39;;
echo intval(160500643816367088/10);//16050064381636710
echo &#39;<br/>&#39;;
echo bcdiv(160500643816367088,10);//16050064381636708
?>

So for sensitive data such as floating point numbers to calculate amounts, it is recommended to use PHP's BC function

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