program FindMostSignificantBit;
{$mode objfpc}{$H+}
uses
SysUtils;
{
Returns the zero-based position of the most significant set bit (MSB)
in an unsigned 64-bit integer.
Examples:
Value = 1 -> 0
Value = 2 -> 1
Value = 8 -> 3
Value = 15 -> 3
Parameters:
Value - Unsigned integer to inspect.
Returns:
-1 if Value is 0 (no bits are set).
Otherwise, the zero-based index of the highest set bit.
}
function MsbPosition(const Value: QWord): Integer;
var
CurrentValue: QWord;
Position: Integer;
begin
if Value = 0 then
Exit(-1);
CurrentValue := Value;
Position := 0;
while CurrentValue > 1 do
begin
CurrentValue := CurrentValue shr 1;
Inc(Position);
end;
Result := Position;
end;
var
Value: QWord;
Position: Integer;
begin
{ Example value. In a real application, this may come from user input. }
Value := 4660; { $1234 }
Position := MsbPosition(Value);
if Position >= 0 then
WriteLn('MSB position of ', Value, ' is ', Position)
else
WriteLn('Value contains no set bits.');
{ Additional test cases }
WriteLn('MSB(1) = ', MsbPosition(1));
WriteLn('MSB(8) = ', MsbPosition(8));
WriteLn('MSB(15) = ', MsbPosition(15));
WriteLn('MSB(0) = ', MsbPosition(0));
end.
{
run:
MSB position of 4660 is 12
MSB(1) = 0
MSB(8) = 3
MSB(15) = 3
MSB(0) = -1
}
