filters.py

from sys import argv
from math import pi, log10, floor

res = [10, 11, 12, 13, 15, 16, 18, 20, 22, 24, 27, 30, 33, 36, 39, 43, 47, 51, 56, 62, 68, 75, 82, 91]
cap = [res[x] for x in range(len(res)) if x % 2 == 0]

pre = {
	'cheb': [[1.231],[1.842],[.597,1.031],[1.582,2.660]],
	'bessel': [[1.272],[1.268],[1.432,1.606],[1.084,1.759]]
}

class SkipValue:
	def __init__(self, arr, index = 0, mult = 0):
		self.index = 0
		self.mult = mult
		self.arr = arr

	def up(self):
		self.index += 1
		if self.index == len(self.arr):
			self.index = 0
			self.mult += 1
		return self.value()

	def down(self):
		self.index -= 1
		if self.index < 0:
			self.index = len(self.arr)-1
			self.mult -= 1
		return self.value()

	def value(self):
		return self.arr[self.index] * 10 ** self.mult

	def toTuple(self):
		return (self.arr[self.index], self.mult, self.value())

def calcGain(k):
	if k <= 0: return None
	best = (1e100, None, None)
	r1 = SkipValue(res, mult = 4)
	while r1.value() >= 1e3:
		r2 = approx(r1.value() * k, res)
		if r2.value() < 1e3 or r2.value() > 1e5:
			r1.down()
			continue
		dist = abs(r2.value() / r1.value() - k)
		if dist < best[0]:
			best = (dist, r1.toTuple(), r2.toTuple())
		r1.down()
	return best

def calcRC(value):
	r = SkipValue(res, mult = 4)
	best = (1e100, None, None)
	while r.value() >= 1e3:
		c = approx(value / r.value(), cap)
		if c.mult < -11 or c.mult > -6:
			r.down()
			continue
		dist = abs(r.value() * c.value() - value)
		if dist < best[0]:
			best = (dist, r.toTuple(), c.toTuple())
		r.down()
	return best

def approx(value, arr):
	valueLog = log10(value)
	base = floor(valueLog)
	index = (valueLog - base) * len(arr)
	up = SkipValue(arr, index = index, mult = base)
	down = SkipValue(arr, index = index, mult = base)
	best = abs(up.value() - value)
	while abs(up.up() - value) < best:
		best = abs(up.value() - value)
	up.down()
	while abs(down.down() - value) < best:
		best = abs(down.value() - value)
	down.up()
	if abs(up.value() - value) < abs(down.value() - value):
		return up
	else:
		return down

poles = int(argv[1])
fc = int(argv[2])
if argv[3] in pre:
	fns = pre[argv[3]][poles-2]
	ks = pre[argv[3]][poles-1]
else:
	fns = list(map(lambda x: float(x), argv[3:3+poles//2]))
	ks = list(map(lambda x: float(x), argv[3+poles//2:4+poles]))

des = 1/(2 * pi * fc)

gains = []
lowpass = []
highpass =[]

for stage in range(poles//2):
	print("Stage",stage)
	fn = fns[stage]
	k = ks[stage]
	print("Fn",fn,"Gain",k)
	gains.append(calcGain(k-1))
	lowpass.append(calcRC(des / fn))
	highpass.append(calcRC(des * fn))

print('G',gains)
print('L',lowpass)
print('H',highpass)