sagemath: compared to r.quantile, what is a faster way to find boundaries for a boxplot?

The following (crude) code is at least 50 times faster than r.quantile:

def findFences (orderedList, outlierC = 1.5, farOutlierC = 3.0):
   """findFences: an ordered list of ints or floats -> tuple of 9 floats
   (aMin, outerLoFence, innerLoFence, Q1, Q2, Q3, innerHiFence, outerHiFence, aMax)
   keys: float for outlier constant [outlierC] and far outlier constant [farOutlierC]"""

   lenMod4, half, quarter = len(orderedList) % 4, int(len(orderedList)/2), int(len(orderedList)/4)

   aMin, aMax = orderedList[0], orderedList[-1]

   # find quartiles
   if not lenMod4: Q1, Q2, Q3 = (orderedList[half-quarter] + orderedList[half-quarter-1])/2.0, (orderedList[half] + orderedList[half-1])/2.0, (orderedList[half+quarter] + orderedList[half+quarter-1])/2.0
   elif lenMod4 == 1: Q1, Q2, Q3 = float(orderedList[half-quarter]), float(orderedList[half]), float(orderedList[half+quarter])
   elif lenMod4 == 2: Q1, Q2, Q3 = float(orderedList[half-quarter-1]), (orderedList[half] + orderedList[half-1])/2.0, float(orderedList[half+quarter])
   else: Q1, Q2, Q3 = (orderedList[half-quarter] + orderedList[half-quarter-1])/2.0, float(orderedList[half]), (orderedList[half+quarter] + orderedList[half+quarter+1])/2.0

   IQR = Q3 - Q1
   outDist = IQR * outlierC 
   farOutDist = IQR * farOutlierC
   innerLoFence, innerHiFence = Q1 - outDist, Q3 + outDist
   outerLoFence, outerHiFence = Q1 - farOutDist, Q3 + farOutDist

   return aMin, outerLoFence, innerLoFence, Q1, Q2, Q3, innerHiFence, outerHiFence, aMax