/** This is an new timing test to see how well Frink's updated routines
    parse large integers more rapidly than Java currently
    does with its BigInteger(String) constructor, which is O(n^2) in the
    number of digits.

    See:
    https://stackoverflow.com/questions/14757086/new-bigintegerstring-performance-complexity?rq=1

    This algorithm is a recursive divide-and-conquer algorithm that is
    extremely simple.  It recursively the string into two approximate halves
    (the halves don't have to be exact,) and calls itself on each half of the
    result.  The result is calculated as:

    parseRecursive[left] * radix^length[right] + parseRecursive[right]

    NOTE:  This currently only handles positive numbers.
*/
parseRecursive[str] :=
{
   len = length[str]

   if len <= 1280             // TODO:  Tune this threshold
      return parseInt[str]   // Bottom case, use non-recursive built-in routine
   
   halfLen = len div 2
   left =   left[str, -halfLen]  // Whatever's left after taking halfLen chars
                                 // from the right
   right = right[str,  halfLen]  // Take exactly halfLen chars from the right

   return parseRecursive[left] * 10^halfLen + parseRecursive[right]
}


// Parse recursively and test the result.  This returns the time taken
// by the parseRecursive call.  It does not include the (possibly much greater)
// time taken by the old parseInt[str] call that it's testing against.
parseRecursiveTest[str, iterations=1] :=
{
   start = now[]
   result = -1
   for i = 1 to iterations
      result = parseRecursive[str]
   end = now[]
   if result != parseInt[str]
      println["Error:\n in:  $str\n out: $result"]
   return end-start
}

// Parse recursively and time the result, returning the time taken.
parseRecursiveTime[str, iterations] :=
{
   start = now[]
   for i = 1 to iterations
      result = parseInt[str]   // Frink native call
   end = now[]
   return end-start
}

// Timing test
lastTime = undef

for k = 1 to 2
for i=1 to 7
{
   n = 10^(10^i) - 1
   str = toString[n]

   iterations = 10^max[7-i, 0]
   time = parseRecursiveTime[str, iterations]
   
   print["Time to parse " + length[str] + " digits ($iterations iterations):\t" + format[time, "ms", 0]]
   
   if lastTime != undef  && lastTime > 0 s && time > 0 s
   {
      time = time/iterations
      order = log[time/lastTime] / log[10]
      println["\tO(n^" + format[order, 1, 3] + ")"]
   } else
      println[]

   lastTime = time
}