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()