Just another update

Task/Pi/Pascal/pi.pascal

@@ -1,27 +1,40 @@
 Program Pi_Spigot;
-
 const
   n   = 1000;
   len = 10*n div 3;
 
 var
-  i, j, k, q, x, nines, predigit: integer;
-  a: array[1..len] of longint;
+  j, k, q, nines, predigit: integer;
+  a: array[0..len] of longint;
+
+function OneLoop(i:integer):integer;
+var
+  x: integer;
+begin
+  {Only calculate as far as needed }
+  {+16 for security digits ~5 decimals}
+  i := i*10 div 3+16;
+  IF i > len then
+    i := len;
+  result := 0;
+  repeat   {Work backwards}
+    x  := 10*a[i] + result*i;
+    result := x div (2*i - 1);
+    a[i]   := x - result*(2*i - 1);//x mod (2*i - 1)
+    dec(i);
+  until i<= 0 ;
+end;
 
 begin
+
   for j := 1 to len do
     a[j] := 2;                 {Start with 2s}
   nines := 0;
   predigit := 0;               {First predigit is a 0}
+
   for j := 1 to n do
   begin
-    q := 0;
-    for i := len downto 1 do   {Work backwards}
-    begin
-      x    := 10*a[i] + q*i;
-      a[i] := x mod (2*i - 1);
-      q    := x div (2*i - 1);
-    end;
+    q := OneLoop(n-j);
     a[1] := q mod 10;
     q := q div 10;
     if q = 9 then
@@ -29,22 +42,22 @@ begin
     else
       if q = 10 then
       begin
-	write(predigit+1);
-	for k := 1 to nines do
-	  write(0);            {zeros}
-	predigit := 0;
-	nines := 0
+        write(predigit+1);
+        for k := 1 to nines do
+          write(0);            {zeros}
+        predigit := 0;
+        nines := 0
       end
       else
       begin
-	write(predigit);
-	predigit := q;
-	if nines <> 0 then
-	begin
-	  for k := 1 to nines do
-	    write(9);
-	  nines := 0
-	end
+        write(predigit);
+        predigit := q;
+        if nines <> 0 then
+        begin
+          for k := 1 to nines do
+            write(9);
+          nines := 0
+        end
       end
   end;
   writeln(predigit);