Question

我有两个数字应该等于返回差异，我没有意义......

能够在这里重现此问题的唯一方法是我必须对我的数组进行base64_encode，

这是脚本：

基本上脚本会将“1 234,5”之类的数字修改为“1234.5”并进行计算，但最终返回

            First Number: 4784.47
            Second Number: 4784.47
            Difference: 9.0949470177293E-13

我只是不明白?????????

            $aa = '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';

            $tt = 'YTozOntzOjE2OiJTdW1tYXJ5SXRlbU5ldHRvIjtzOjg6IjMgODI3LDU4IjtzOjE0OiJTdW1tYXJ5SXRlbVZBVCI7czo2OiI5NTYsODkiO3M6MTc6IlN1bW1hcnlJdGVtQnJ1dHRvIjtzOjg6IjQgNzg0LDQ3Ijt9';

            $a = unserialize(base64_decode($aa));
            $t = unserialize(base64_decode($tt));


            function calculate_call_fees($a,$t){

                $or_item = 0;

                foreach($a as $k => $r) {
                    $or_item += fix_num($r['GrossAmount']); 
                }        

                $br =  fix_num($t['SummaryItemBrutto']);   

                if($br>$or_item){
                    $diff = $br-$or_item;
                } else {
                    $diff = 0;
                }

                echo 'First Number: ' . $br.'<br/>';
                echo 'Second Number: ' . $or_item.'<br />';
                echo 'Difference: ' . $diff.'<br />';

                echo '<hr />';
                echo '<pre>';
                print_r($a);
                echo '</pre>';
                echo '<hr />';
                echo '<pre>';
                print_r($t);
                echo '</pre>';    

            }

            function fix_num($n){
                return floatval(str_replace(Array(" ",","),array("","."),$n));
            }

            calculate_call_fees($a,$t);

Answer 1

使用“等于”与浮点数进行比较是危险的，因为浮点数限制精度 - 由于涉及舍入，您可能会得到很小的差异。

相反，如果您想查看两个浮点数是否“相同”，只需看看它们的差异是否低于某个阈值：

if( abs($a - $b) < 0.00000001) {
    // a and b are "equal"
}

Answer 2

这不仅仅是PHP。存在表示计算机中的分数的一般问题。它受各种类型的溢出，下溢，精度问题等的影响。 PHP's manual阐明了这个话题。

一般规则 - 如果要求两个'似乎相等'的数字保证相等 - 不要使用浮点数据类型（浮点数，双精度数），而是使用固定点数（十进制数字）

Answer 3

看来这是“机器epsilon”问题： http://en.wikipedia.org/wiki/Machine_epsilon

尝试将它们之间的差异与0.000001进行比较，而不是直接比较它们。

如何在PHP中两个相等的数字不相等

3 个答案: