The Shl keyword performs a bitwise shift left of an Integer. The number is shifted Bits to the left.
If Bits is greater than the size of the number type, the Bits value is Mod'ed by the number type size before the shift.
myByte : Byte;
myByte := $2F; // $2F = 47 decimal
myByte := myByte Shl $24;
Gives the same result as Shl 4 = $F0.
Warning Only use Shl when a bit operation is required - do not use instead of a multiplication or division. First because it is unclear as to what is happening. Secondly, bits may be lost in the operation.
Example code : Shifting left and losing high bits before shifting back
before, after : Word;
begin // Set up out starting number before := $3C; // Hex 3C = 003C in the Word // Shift left by 12 will lose the top 12 bits of the Word
after := before Shl 12;
ShowMessageFmt('Before : %x',[before]);
ShowMessageFmt('After shift left : %x',[after]); // Shifting right by 12 will not recover the lost data
after := after Shr 12;
ShowMessageFmt('After shift right : %x',[after]);