function [ num_zc ] = count_zerocrosses( data )
%COUNT_ZEROCROSSES Sums the number of times data entries go from 1 to -1,
%   -1 to 1, 1 00000 -1,  1 0000 1, and -1 0000 -1.
len = length(data);
num_zc = sum(0.5*abs(sign(data(2:len))-sign(data(1:len-1))));