numbers in array arr
l = low(arr)
h = high(arr)
m = (l + h) div 2

while true:
  hm = (h + m) div 2
  if (arr[m] < arr[hm]) and (arr[hm] < arr[h]):
    h = m
    m = (l + m) div 2
  else:
    l = m
    m = hm
  if (l + 1 = m) and (m + 1 = h):
    pivot = m
    exit