为什么在JS中将5726718050568503296截断 [英] Why is 5726718050568503296 truncated in JS

问题描述

根据标准 ES将数字实现为IEEE754加倍.

As per the standard ES implements numbers as IEEE754 doubles.

并且根据 https://www.binaryconvert.com/result_double.html?decimal=053055050054055049056048053048053054056053048051050057054 和其他编程语言 https://play.golang.org/p/5QyT7iPHNim看起来 5726718050568503296 值可以精确地表示而不会损失精度.

And per https://www.binaryconvert.com/result_double.html?decimal=053055050054055049056048053048053054056053048051050057054 and other programming languages https://play.golang.org/p/5QyT7iPHNim it looks like the 5726718050568503296 value can be represented exactly without losing precision.

为什么它在JS中丢失3个有效数字(最新稳定的Google chrome和firefox中转载了此内容)

Why it loses 3 significant digits in JS (reproduced in latest stable google chrome and firefox)

此问题最初是从在golang中复制javascript不安全数字触发的

该值绝对可以在双IEEE754中表示，请参阅如何在Go中将裸比特转换为float64: https://play.golang.org/p/zMspidoIh2w

The value is definitely representible in double IEEE754, see how naked bits are converted to a float64 in Go: https://play.golang.org/p/zMspidoIh2w

推荐答案

转换 Number <时JavaScript的默认规则/code>值转换为十进制数字是使用足够的数字来区分 Number 值.具体来说，这是根据链接的答案来自ECMAScript 2017语言规范第7.1.12.1节中的第5步产生的.(2020年版本为6.1.6.1.20.)

The default rule for JavaScript when converting a Number value to a decimal numeral is to use just enough digits to distinguish the Number value. Specifically, this arises from step 5 in clause 7.1.12.1 of the ECMAScript 2017 Language Specification, per the linked answer. (It is 6.1.6.1.20 in the 2020 version.)

因此，虽然可以表示5,726,718,050,568,503,296，但打印时会产生"5726718050568503000"，因为足以将其与相邻的可表示值(5,726,718,050,568,502,272和5,726,718,050,568,504,320)区分开来.

So while 5,726,718,050,568,503,296 is representable, printing it yields "5726718050568503000" because that suffices to distinguish it from the neighboring representable values, 5,726,718,050,568,502,272 and 5,726,718,050,568,504,320.

与 x.toPrecision(21)中一样，您可以请求使用 .toPrecision 转换为字符串时更精确.

You can request more precision in the conversion to string with .toPrecision, as in x.toPrecision(21).

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