Data update

Task/Long-multiplication/PascalABC.NET/long-multiplication.pas

@@ -0,0 +1,56 @@
+function longmulti(a, b: string): string;
+begin
+  var i := 0;
+  var j := 0;
+  var k := false;
+
+  // either is zero, return "0"
+  if (a = '0') or (b = '0') then
+  begin
+    result := '0';
+    exit;
+  end;
+
+  // see if either a or b is negative
+  if a[1] = '-' then
+  begin
+    i := 2;
+    k := not k;
+  end;
+  if b[1] = '-' then
+  begin
+    j := 2;
+    k := not k;
+  end;
+
+  // if yes, prepend minus sign if needed and skip the sign
+  if (i > 1) or (j > 1) then
+  begin
+    result := if k then '-' else '';
+    result += longmulti(a[i:a.Length + 1], b[j:b.Length + 1]);
+    exit;
+  end;
+
+  result := '0' * (a.length + b.length);
+
+  for var ii := a.length downto 1 do
+  begin
+    var carry := 0;
+    var kk := ii + b.length;
+    for var jj := b.length downto 1 do
+    begin
+      var n := a[ii].todigit * b[jj].todigit + result[kk].todigit + carry;
+      carry := n div 10;
+      result[kk] := chr(n mod 10 + ord('0'));
+      dec(kk);
+    end;
+    result[kk] := chr(ord(result[kk]) + carry);
+  end;
+
+  if result[1] = '0' then
+    result[1:result.length] := result[2:result.length + 1];
+end;
+
+begin
+  longmulti('-18446744073709551616', '-18446744073709551616').println;
+end.