program CopyBitsPascal;
{
Handles edge cases:
- Validates i and j
- Prevents undefined behavior from shifting by ≥ 64 bits
- Masks M so only the required bits are copied
}
{ Convert unsigned 64‑bit integer to binary string without leading zeros }
function ToBinary(x: QWord): string;
var
s: string;
begin
if x = 0 then
begin
ToBinary := '0';
Exit;
end;
s := '';
while x > 0 do
begin
if (x and 1) = 1 then
s := '1' + s
else
s := '0' + s;
x := x shr 1;
end;
ToBinary := s;
end;
{ Copy bits from M into N between bit positions [i, j] }
function CopyBits(N, M: QWord; i, j: Integer): QWord;
var
length: Integer;
mask: QWord;
N_cleared: QWord;
M_shifted: QWord;
begin
if (i < 0) or (j < 0) or (i > j) or (j >= 63) then
begin
Writeln('Error: Invalid bit range');
Halt(1);
end;
length := j - i + 1;
{ Mask for bits i..j }
mask := ((QWord(1) shl length) - 1) shl i;
{ Clear bits i..j in N }
N_cleared := N and (not mask);
{ Take only the needed bits from M and shift into place }
M_shifted := (M and ((QWord(1) shl length) - 1)) shl i;
CopyBits := N_cleared or M_shifted;
end;
var
N, M, R: QWord;
begin
{
N: 100 011111 00
M: 110011
Result: 100 110011 00
}
N := %10001111100; { Pascal binary literal }
M := %110011;
R := CopyBits(N, M, 2, 7);
Writeln('N: ', ToBinary(N));
Writeln('M: ', ToBinary(M));
Writeln('Result: ', ToBinary(R));
end.
{
OUTPUT:
N: 10001111100
M: 110011
Result: 10011001100
}
