javascript - 获取号码18437736874454810627

Question

ECMAScript Number 类型正好有 18437736874454810627 个值。

他们为什么会得出这个数字(18437736874454810627)？换句话说，因为计算机通常基于二进制系统，所以几乎所有数字(如位、字节、int16、int32 等)都基于 2。但我看不出我们如何从 18437736874454810627 到 2。

Answer 1

因为 floating point number JavaScript 使用的位数固定，如 ECMA standard 中所述使用(PDF 的第 41 页，或页脚中所写的第 29 页)。

The Number type has exactly 18437736874454810627 (that is, 2^64 - 2^53 + 3) values, representing the double-precision 64-bit format IEEE 754 values as specified in the IEEE Standard for Binary Floating-Point Arithmetic, except that the 9007199254740990 (that is, 2^53 - 2) distinct "Not-a-Number" values of the IEEE Standard are represented in ECMAScript as a single special NaN value.