x64 中的枚举集大小 [英] Enumeration set size in x64

问题描述

我发现 32 位和 64 位的 SizeOf(set) i 不同，下面的示例显示 32 位的 5 个字节和 64 位的 8 个字节.但是我没有发现有关 64 位 SizeOf(sets) 变化的信息.是否有任何关于它的 Embarcadero 文档或编译器指令可以在 32 位和 64 位上获得类似的结果.

I found that a SizeOf(set) i different in 32-bit and 64-bit, the example below shows 5 byte for 32-bit and 8 for 64-bit. But i found nothing information about changes in SizeOf(sets) for 64-bit. Is there any Embarcadero documentation about it or compiler directive to get a similar results on 32 and 64-bit.

program Project1;

{$APPTYPE CONSOLE}
{$R *.res}

uses System.SysUtils;

type
{ Enumeration of properties}
TProperty1 = (p1, p2, p3, p4, p5, p6, p7, p8, p9, p10, p11, p12, p13, p14,
  p15, p16, p17, p18, p19, p20, p21, p22, p23, p24, p25, p26, p27, p28,
  p29, p30, p31, p32, p33, p34, p35, p36, p37);

TProperties1 = set of TProperty1;

begin
WriteLn(SizeOf(TProperties1));
ReadLn;
end.

推荐答案

回答您的问题.我在 Embarcadero 网站上找不到任何关于差异或编译器指令来改变行为的信息.我的研究表明:

To answer your question. I couldn't find anything on the Embarcadero site regarding the differences or a compiler directive to change the behavior. My research indicates the following:

集合在 32 位中具有以下大小(以字节为单位):

Sets have the following sizes in bytes in 32 bit:

• 最多 8 个元素 - 1 个字节
• 9 到 16 个元素 - 2 个字节
• 17 到 32 个元素 - 4 个字节

从这一点开始，它会根据需要添加字节，一次一个.所以33到40个元素使用5个字节，41到48个元素使用6个字节.

From this point onwards it adds adds bytes as needed, one at a time. So 33 to 40 elements uses 5 bytes and 41 to 48 elements uses 6 bytes.

在 64 位模式下，情况略有不同:

In 64 bit mode, things are slightly different:

• 最多 8 个元素 - 1 个字节
• 9 到 16 个元素 - 2 个字节
• 17 到 32 个元素 - 4 个字节
• 33 到 64 个元素 - 8 字节

从这一点开始，它会根据需要添加字节，一次一个.所以65到72个元素使用9个字节，73到80个元素使用10个字节.

From this point onwards it adds adds bytes as needed, one at a time. So 65 to 72 elements uses 9 bytes and 73 to 80 elements uses 10 bytes.

为了解决这个问题，你需要在 TWriter.WriteProperty 和 TReader.ReadSet 中使用类似 WriteSet 的东西，或者你可以做这样的事情:

To get around this you are going to need to either use something like WriteSet in TWriter.WriteProperty and TReader.ReadSet or you can do something like this:

procedure SaveSetToStream(aStream: TStream; const aSet: TProperties1);
var
  streamData: array[0..7] of byte;
begin
  Assert(SizeOf(aSet) <= SizeOf(streamData), 'Set is too large to save. Increase the array length.');
  FillChar(streamData, SizeOf(streamData), 0);
  Move(aSet, streamData, SizeOf(aSet));
  aStream.Write(streamData, SizeOf(streamData));
end;

function ReadFromStream(aStream: TStream): TProperties1;
var
  streamData: array[0..7] of byte;
begin
  Assert(SizeOf(Result) <= SizeOf(streamData), 'Set is too large to load. Increase the array length.');
  aStream.Read(streamData, SizeOf(streamData));
  Move(streamData, Result, SizeOf(Result));
end;

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