Mega Code Archive
Endian swap for numeric types
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Title: Endian swap for numeric types
Question: Convert WORD and DWORD sized variables to/from little-endian and big-endian format numbers. Useful when loading files using big-endian numeric format.
Answer:
If you need to load and manipulate files created on non-intel
based applications, chances are that the numeric types are stored
in big-endian format. This procedure basically reverses the byte ordering of numbers stored in big-endian format to the intel native little-endian format. Big/Little endian format applies to floating point and integer types that are 2 or 4 bytes in length. I use it for loading LightWave3D objects. LightWave was originally written for legacy Amiga computers which were motorola 68000 based.
I hope you find it useful.
(******************* EndianSwap *************************
Purpose: Reverses byte ordering for numeric types
"Big-Endian" "Little-Endian" conversion
Input: ValueIn: Pointer
The address a WORD or DWORD sized numeric variable
on which to perform the byte swap.
Size: integer;
The length in bytes of the numeric type.
Note: Requires a 486+ for execution of BSWAP
******************* EndianSwap *************************)
procedure EndianSwap(ValueIn: Pointer; Size: integer);
var
l: LongWord;
w: Word;
begin
case Size of
2: begin
{ ValueIn is WORD-sized }
w := PWord(ValueIn)^;
asm
mov ax,w; { move w into ax register }
xchg al,ah; { swap lo and hi byte of word }
mov w,ax; { move "swapped" ax back to w }
end;
PWord(ValueIn)^ := w;
end;
4: begin
{ ValueIn is DWORD-sized }
l := PLongWord(ValueIn)^;
asm
mov eax,l; { move l into eax register }
BSWAP eax; { reverse the order of bytes in eax }
mov l,eax; { move "swapped" eax back to 1 }
end;
PLongWord(ValueIn)^ := l;
end;
end;
end;
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