mod of a range

mod_range.py

# given a number in the range [amin, amax] (inclusive)
# what are the min and max of that number after modding it by b?

# c style modulus
def modn(a, b): return -((-a)%b) if a < 0 else a%b

# aka a fast version of
def slow_modrange(amin, amax, b):
  values = [modn(rv, b) for rv in range(amin, amax+1)]
  return min(values), max(values)

# ...long answer relegated to history...

# or, if you like short. with help from the tinygrad discord:
def fast_modrange(amin, amax, b):
  if amin < 0 and amax >= 0: return (max(-b+1, amin), min(amax, b-1))
  m1, m2 = modn(amin, b), modn(amax, b)
  if amax - amin >= b or (m1 >= m2 and amin != amax): return (0, b-1) if amin >= 0 else (-b+1, 0)
  return m1, m2