This article was originally posted to delphi3000.com
Sometimes it is nessescary to turn the bytes of an integer. This is known as the big-endian/little-endian problem, and occurs when you receive data from a machine with another byte order:
Some machines arranges bytes from left to right.
Other arranges them from right to left.
Delphi has implemented a function called swap() that can turn integers. But here are some examples on how to do it yourself.
// Turning a smallint (16 bit signed)
function i16( i : smallint ) : smallint;
var
x1 : smallint;
x2 : array[0..1] of byte absolute x1;
x3 : array[0..1] of byte absolute i;
begin
x2[0] := x3[1];
x2[1] := x3[0];
result := x1;
end;
// Turning a word (16 bit unsigned)
function r16( i : word) : word;
var
x1 : word;
x2 : array[0..1] of byte absolute x1;
x3 : array[0..1] of byte absolute i;
begin
x2[0] := x3[1];
x2[1] := x3[0];
result := x1;
end;
// Turning a longint (32 bit signed)
function r32( i : longint) : longint;
var
x1 : longint;
x2 : array[1..4] of byte absolute x1;
x3 : array[1..4] of byte absolute i;
begin
x2[1] := x3[4];
x2[2] := x3[3];
x2[3] := x3[2];
x2[4] := x3[1];
result := x1;
end;
Do you see the pattern?