IEEE754浮点值的便携式系列化 [英] Portable serialisation of IEEE754 floating-point values

问题描述

我最近一直在努力，需要存储和加载大量数据，包括单precision浮点值的系统上。我决定在网络字节顺序标准化整数，并决定将储存浮点值big-endian格式，即：

I've recently been working on a system that needs to store and load large quantities of data, including single-precision floating-point values. I decided to standardise on network byte order for integers, and also decided to store floating point values in big-endian format, i.e.:

  |-- Byte 0 --| |-- Byte 1 -|  Byte 2   Byte 3
  #      ####### #     ####### ######## ########
Sign     Exponent          Mantissa
 1b    8b, MSB first    23b, MSB first

在理想情况下，我想提供像 htonl函数（）和 ntohl（），因为我已经使用这些用于擦拭整数，我也希望有尽可能多的平台无关性越好（而假设浮动类型对应IEEE754 32的方式来实现这一位浮点值）。有没有一些方法，可能使用 ieee754.h ，要做到这一点？

Ideally, I want to provide functions like htonl() and ntohl(), since I have already been using these for swabbing integers, and I also want to implement this in a way that has as much platform-independence as possible (while assuming that the float type corresponds to IEEE754 32-bit floating point values). Is there some way, possibly using ieee754.h, to do this?

我有一个答案似乎的工作，我会发布它下面，但它似乎pretty慢，效率低，我想AP preciate如何使任何建议它更快和/或更可靠。

I have one answer that seems to work, and I will post it below, but it seems pretty slow and inefficient and I would appreciate any suggestions about how to make it faster and/or more reliable.

推荐答案

简单得多，并且根据同样的假设和你（其是浮点和整数类型具有相同的字节顺序，并且是几乎普遍有效的 - 现实的你永远不会遇到一个系统，这是不正确的）：

Much simpler, and depending on the same assumption as yours (which is that float and integer types have the same byte order, and is almost universally valid -- realistically you'll never encounter a system where it isn't true):

#include <string.h>

float htonf(float val) {
    uint32_t rep;
    memcpy(&rep, &val, sizeof rep);
    rep = htonl(rep);
    memcpy(&val, &rep, sizeof rep);
    return val;
}

任何相当不错的编译器将优化掉两个的memcpy 通话;他们是present击败过于急切严格别名优化，所以这最终是为 htonl 高效加一个函数调用的开销。

Any reasonably good compiler will optimize away the two memcpy calls; they are present to defeat over-eager strict aliasing optimizations, so this ends up being as efficient as htonl plus the overhead of a single function call.

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