Question

感谢堆栈，我了解了浮点不精确，所以我去了bc函数。

这对于“普通”浮动效果很好，但是对于非常小的浮点数，比如10^-10类型，bcadd总是给出0。

有人能告诉我我做错了什么才能让这些小花车精确添加？

非常感谢提前！

PHP

$numerator = 1;
$denominator = 1000000000;
$quotientOne = $numerator / $denominator;

$numerator = 1;
$denominator = 1000000000000000;
$quotientTwo = $numerator / $denominator;

$smallSum = bcadd($quotientOne, $quotientTwo, 100);

echo $quotientOne . "<br>";
echo $quotientTwo . "<br>";
echo $smallSum . "<br>";

给出

1.0E-9
1.0E-15
0.0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000

Answer 1

The / operator返回浮点数或整数。它干扰了您正确使用bcadd（）的尝试。在bcadd（）有机会展示其内容之前，浮点运算的局限性将会持续。

echo gettype($numerator / $denominator);
double

请改用bcdiv()。请注意，bc *（）函数将字符串作为参数，并且它们也返回一个字符串。

$ cat code/php/test.php
<?php
$num_1 = 1;
$denom_1 = 1000000000;

# Cast values to string type to be crystal clear about what you're doing.
$q_1 = bcdiv((string)$num_1, (string)$denom_1, strlen($denom_1));
printf("q_1: %s\n", $q_1);

$num_2 = 1;
$denom_2 = 1000000000000000;

# php will do an implicit conversion to string anyway, though.
$q_2 = bcdiv($num_2, $denom_2, strlen($denom_2));
printf("q_2: %s\n", $q_2);

printf("sum: %s\n", bcadd($q_1, $q_2, strlen($denom_2)));
?>

$ php code/php/test.php
q_1: 0.0000000010
q_2: 0.0000000000000010
sum: 0.0000000010000010

任意精度算术本质上比浮点算术慢。这是您为数十，数百或数千个精度数字支付的价格。

bcadding非常小的花车给出0

1 个答案: