from __future__ import generators
import random


def firstn(g, n):
	for i in range(n):
		yield g.next()

def signal():
		while 1:
			yield random.randrange(-5, 5)

def cross_detect(a, b):
	if ((a > 0) and (b < 0)): return -1
	elif ((a < 0) and (b > 0)): return 1
	else: return 0

def zerocross(g):
	a = g.next()
	b = g.next()
	while 1:
		yield cross_detect(a, b)
		a, b = b, g.next()
		
def smooth(g):
	a = g.next()
	b = g.next()
	while 1:
		yield (a+b)/2.0
		a, b = b, g.next()