去班次太大了(Go shift count too large)

去班次太大了(Go shift count too large)

在Go的常量规范中 ，提到：

数字常量表示任意精度的精确值，不会溢出。

所以我试过了

const VeryVeryBigNumber = 1 << 200

它的工作原理。 但是，我可以尝试的最大移位数是511，使用512会抛出：

shift count too large: 512 。

512代表什么？ 我无意使用它，我只是想知道为什么它在我的机器中限制为511（我使用ubuntu 64位并且去1.9.2）？

谢谢

In Go's constant specification, it is mentioned that:

Numeric constants represent exact values of arbitrary precision and do not overflow.

So I tried

const VeryVeryBigNumber = 1 << 200

and it works. However, the biggest shift count I could try is 511 and using 512 will throw:

shift count too large: 512.

What does 512 represents? I have no intention to use it, I just want to know why is it limited to 511 in my machine (I'm using ubuntu 64 bit and go 1.9.2)?

Thanks

最满意答案

512是任意限制。 规范唯一说的是：

实现限制：虽然数字常量在语言中具有任意精度，但编译器可以使用精度有限的内部表示来实现它们。 也就是说，每个实施必须：

表示至少256位的整数常量。

不幸的是， 围绕限制的评论并没有给出理由。

在某些时候，必须使用限制。 我建议坚持要求的256。

512 is kind of an arbitrary limit. The only thing the spec says is:

Implementation restriction: Although numeric constants have arbitrary precision in the language, a compiler may implement them using an internal representation with limited precision. That said, every implementation must:

Represent integer constants with at least 256 bits.

Unfortunately, the comments around the limits don't give a reason.

At some point, a limit has to be used. I would recommend sticking to the required 256.