将双 精度浮 点值按指定的小数位数舍入。

Rounds a double - precision floating - point value to the specified number of fractional digits.

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用其他的话来讲，展开形式是一种方式，把数给分开，并且将它作为一个各数字（是单独的数位上的数字）值的和来表达它。

In other words, expanded form is the method of pulling a number apart and expressing it as a sum of the values of each digit.

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由于杂凑值将大量资料表示成较小的数值，因此杂凑值可用于数位签章。

Hash values represent large amounts of data as much smaller numeric values, so they are used with digital signatures.

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