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PHP中浮点数精密度的警告

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Jun 13, 2016 am 10:55 AM

intphp

PHP中浮点数精度的警告

这个是PHP document中给出来的提示：

简单的十进制分数如同 0.1 或 0.7 不能在不丢失一点点精度的情况下转换为内部二进制的格式。

floor(( 0.1 + 0.7 ) * 10)? ?返回 7 而不是8，

(int)(( 0.1 + 0.7 ) * 10) ?返回7而不是8.

对这种现象的解释是“因为该结果内部的表示其实是类似 7.9”。

所以得到的结论是：

所以永远不要相信浮点数结果精确到了最后一位，也永远不要比较两个浮点数是否相等。

决不要将未知的分数强制转换为Int。

(int)round( 0.1 + 0.7 ) * 10) 这样似乎就安全了。

在有大量乘除或者是中间值为float类型时，为了数值精度还是使用BC math函数了。

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