Byte Manipulation

[flywire]

How do I rewrite this delphi code for lazurus using lo:

buffer[1]:=LoByte(LoWord(TOCfilesCount));
...
buffer[4]:=HiByte(HiWord(TOCfilesCount));

Where buffer is a byte array and TOCfilesCount is a LongInt.

[engkin]

Code: [Select]

  PLongInt(@buffer[1])^ := TOCfilesCount;


[balazsszekely]

If you are on windows just add windows to the uses clauses and you're good to go.

Code: [Select]

uses windows;
//...
   buffer[1]:=LoByte(LoWord(TOCfilesCount));           
   buffer[4]:=HiByte(HiWord(TOCfilesCount));
//...


[engkin]

The OP wants buffer[2] and buffer[3] as well.

[Awkward]

as alternative:

type
  tTempRecord = record
    case boolean of
      true: (a:longint);
      false: (b:array [0..3] of byte);
  end;

and in code:
  buffer[1]:=tTempRecord(TOCfilesCount).b[0];

as example. no?

[engkin]

Yes, sure!

I wonder if the OP is trying to implement BEtoN.

[marcov]

Code: [Select]

  PLongInt(@buffer[1])^ := TOCfilesCount;


Note that this is not entirely equivalent, for some architectures throw exceptions when you access 32-bits values that are not aligned. In such case the former works.

Putting

Code: [Select]

unaligned(  PLongInt(@buffer[1])^) := TOCfilesCount;

Might work too

http://www.freepascal.org/docs-html/ref/refse73.html

[engkin]

I'm not familiar with unaligned, it makes perfect sense. Thanks!

[marcov]

I'm not familiar with unaligned, it makes perfect sense. Thanks!

I know you are a more intermediate user who gives a lot of support, so I just thought I mention it so you have at least heard of it once. I also mostly know it exists, and am not doing it routinely correct myself.

That can be easily seen because my use (written from memory) is different from the manual, the doc seem to indicate that you need to put unaligned over the pointer (the @ expression). At least according to docs.

In general even large parts of packages/ are not ready for this.

[flywire]

If you are on windows just add windows to the uses clauses and you're good to go.

Thanks all ... we have a winner! [Where is the emoticon for remove hat and take a bow?]

[BeniBela]

On which platforms does this matter?

ARM?

[marcov]

On which platforms does this matter?

ARM?

Older ARMs, and some of the more embedded ARMs inherit this.

[Nitorami]

Is there a specific reason why we would not take over over the code directly, just replacing "LoByte" etc. by Lo and Hi ?

Code: [Select]

 
  buffer[1] := Lo(Lo(TOCFilesCount));
  buffer[2] := Lo(Hi(TOCFilesCount));
  buffer[3] := Hi(Lo(TOCFilesCount));
  buffer[4] := Hi(Hi(TOCFilesCount));


[marcov]

IIRC some of those are overloaded, which makes it easy to make errors. I avoid them for that reason.

iword and loword etc are Windows API macros. Both FPC and Delphi probably have them in unit Windows.

[flywire]

If you are on windows just add windows to the uses clauses and you're good to go.

Code: [Select]

uses windows;
//...
   buffer[1]:=LoByte(LoWord(TOCfilesCount));           
   buffer[4]:=HiByte(HiWord(TOCfilesCount));
//...


There seems to be a bug with the Delphi conversion tool. The original Delphi code (too large to load) has 'windows' in the uses clauses but when I convert it the 'windows' clause is removed leading to an error when I compile it. When I reenter it then the code compiles without error. One for the development team?