htmldoc/html/log2_m_8m_source.html

 function log2M = log2M(M)

 if ~isscalar(M) || ~isreal(M) || M<1 || ~isfinite(M)
     error('M must be a positive real finitie scalar.');
 end
 log2M = log2(M);
 if ~iswhole(log2M) || log2M<1
     error('M must be a number 2^k, where k is a positive integer.');
 end
iswhole
function iswhole(in x, in tol)
Determine whether or not input is a whole number.