value = coefficient * 10exponent
是以 10 為底。
0 與 NaN 是特別處理：
There are 255 possible representations of zero. They are all considered to be equal.
There is a special value called nan that has a coefficient of 0 and an exponent of -128. The result of division by zero is nan. nan is also the result of operations that produce results that are too large to be represented. nan is equal to itself.
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