import random

import unittest

from unittest import TestCase

from gf256 import _gfmul

from gf256 import *

class TestGF256(TestCase):

	def test_gfmul(self):

		self.assertEqual(_gfmul(0,0), 0)

		self.assertEqual(_gfmul(1,1), 1)

		self.assertEqual(_gfmul(2,2), 4)

		self.assertEqual(_gfmul(0,21), 0)

		self.assertEqual(_gfmul(0x53,0xca), 0x01)

		self.assertEqual(_gfmul(0xff,0xff), 0x13)

	def testGfmul(self):

		for a in range(256):

			for b in range(256):

				self.assertEqual(_gfmul(a,b), gfmul(a,b))

	def testEvaluate(self):

		for x in range(256):

			(a0,a1,a2,a3)=(x,x>>1,x>>2,x>>3)

			self.assertEqual(evaluate([17],x), 17) # constant polynomial

			self.assertEqual(evaluate([a0,a1,a2,a3],0), x) # any polynomial at 0

			self.assertEqual(evaluate([a0,a1,a2,a3],1), a0^a1^a2^a3) # polynomial at 1 == sum of coefficients

	def testGetConstantCoef(self):

		self.assertEqual(getConstantCoef((1,1),(2,2),(3,3)), 0)

		random.seed(17)

		randomMatches=0

		for i in range(10):

			k=random.randint(2,255)

			# exact

			res=self.checkCoefsMatch(k,k)

			self.assertEqual(res[0], res[1])

			# overdetermined

			res=self.checkCoefsMatch(k,256)

			self.assertEqual(res[0], res[1])

			# underdetermined => random

			res=self.checkCoefsMatch(k,k-1)

			if res[0]==res[1]:

				randomMatches+=1

		self.assertLess(randomMatches, 2) # with a chance (255/256)**10=0.96 there should be no match

	def checkCoefsMatch(self,k,m):

		coefs=[random.randint(0,255) for i in range(k)]

		points=[(j, evaluate(coefs,j)) for j in range(1,256)]

		random.shuffle(points)

		return (getConstantCoef(*points[:m]), coefs[0])

if __name__ == '__main__':

	unittest.main()