Mega Code Archive
Shl - shift an integer value left by a number of bits
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Number Shl bits
Description
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.
For example;
var
myByte : Byte;
begin
myByte := $2F; // $2F = 47 decimal
myByte := myByte Shl $24;
end;
Gives the same result as Shl 4 = $F0.
Notes
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.
Related commands
Hi Returns the hi-order byte of a (2 byte) Integer
Lo Returns the low-order byte of a (2 byte) Integer
Shr Shift an integer value right by a number of bits
Example code : Shifting left and losing high bits before shifting back
var
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]);
end;
Show full unit code
Before : 3C
After shift left : C000
After shift right : C
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