如何将大端数字转换为本地数字delphi [英] how to convert big-endian numbers to native numbers delphi

问题描述

我想知道如何在Delphi中将大端数字转换为本地数字。我在移植一些C ++代码时碰到了这样的问题：

I want to know how to convert big-endian numbers to native numbers in Delphi. I am porting some C++ code in that I came across:

unsigned long blockLength  = *blockLengthPtr++ << 24;
blockLength |= *blockLengthPtr++ << 16;
blockLength |= *blockLengthPtr++ << 8;
blockLength |= *blockLengthPtr;

unsigned long dataLength  = *dataLengthPtr++ << 24;
dataLength |= *dataLengthPtr++ << 16;
dataLength |= *dataLengthPtr++ << 8;
dataLength |= *dataLengthPtr;

我对C ++不熟悉，所以我不理解这些运算符的作用。

I am not familiar with C++, so I don't understand what those operators do.

推荐答案

安德烈亚斯（Andreas）的回答是一个很好的例子，说明如何以纯Pascal进行操作，但是它仍然有点尴尬，就像C ++代码一样。实际上，这可以在单个汇编指令中完成，尽管取决于您使用的是32位还是16位整数：

Andreas's answer is a pretty good example of how to do it in pure pascal, but it still looks kinda awkward, just like the C++ code. This can actually be done in a single assembly instruction, though which one depends on whether you're using 32-bit or 16-bit integers:

function SwapEndian32(Value: integer): integer; register;
asm
  bswap eax
end;

function SwapEndian16(Value: smallint): smallint; register;
asm
  rol   ax, 8
end;

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