int_least64_t 与 int_fast64_t 与 int64_t [英] int_least64_t vs int_fast64_t vs int64_t

问题描述

我正在尝试将我的代码移植到 64 位.

I'm trying to port my code to 64bit.

我发现 C++ 提供了 64 位整数类型，但我仍然对此感到困惑.

I found that C++ provides 64bit integer types, but I'm still confused about it.

首先，我找到了四种不同的 64bit ints:

First, I found four different 64bit ints:

int_least64_t
int_fast64_t
int64_t
intmax_t

和它们未签名的对应物.我使用 sizeof() 测试了它们，它们是 8 字节，所以它们是 64 位.

and their unsigned counterparts. I tested them using sizeof() and they are 8 byte so they are 64bit.

它们之间有什么不同?least 和 fast 类型的含义是什么?intmax_t 怎么样?

What's the different between them? What is the meaning of the least and fast types? What about intmax_t?

推荐答案

在您的平台上，它们都是相同基础数据类型的名称.在其他平台上，它们不是.

On your platform, they're all names for the same underlying data type. On other platforms, they aren't.

int64_t 必须为 64 位.在(例如)具有 9 位字节的体系结构上，它根本不可用.

int64_t is required to be EXACTLY 64 bits. On architectures with (for example) a 9-bit byte, it won't be available at all.

int_least64_t 是至少 64 位的最小数据类型.如果 int64_t 可用，它将被使用.但是(例如)对于 9 位字节的机器，这可能是 72 位.

int_least64_t is the smallest data type with at least 64 bits. If int64_t is available, it will be used. But (for example) with a 9-bit byte machine, this could be 72 bits.

int_fast64_t 是至少 64 位且算术性能最好的数据类型.它的存在主要是为了与 int_fast8_t 和 int_fast16_t 保持一致，它们在许多机器上将是 32 位，而不是 8 位或 16 位.再过几年，可能会有一个架构128 位数学比 64 位更快，但我认为今天不存在.

int_fast64_t is the data type with at least 64 bits and the best arithmetic performance. It's there mainly for consistency with int_fast8_t and int_fast16_t, which on many machines will be 32 bits, not 8 or 16. In a few more years, there might be an architecture where 128-bit math is faster than 64-bit, but I don't think any exists today.

如果您要移植算法，您可能希望使用 int_fast32_t，因为它会保存您的旧 32 位代码可以处理的任何值，但如果速度更快，它将是 64 位.如果您要将指针转换为整数(为什么?)，请使用 intptr_t.

If you're porting an algorithm, you probably want to be using int_fast32_t, since it will hold any value your old 32-bit code can handle, but will be 64-bit if that's faster. If you're converting pointers to integers (why?) then use intptr_t.

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