java - Determine if a number is power of 4, logNum % logBase == 0 vs (logNum / logBase) % 1 == 0 -

problem: check if number power of 4.

my solution in java:

public static boolean ispoweroffour(int num) {     return (math.log(num) % math.log(4) == 0); } 

but seems off in cases, example when num 64.

i found out if change code little bit, works well.

public static boolean ispoweroffour(int num) {     return (math.log(num) / math.log(4) %1 == 0); } 

i think both solutions same thing, check if remaining of lognum/logbase 0. why first solution doesn't work? because solution incorrect or relative low level jvm stuff? thanks.

building on @dasblinkenlight's answer, can combine both conditions (first, power of 2, power of 4 among possible powers of 2) simple mask:

public static boolean ispoweroffour(int num) {   return ((( num & ( num - 1 )) == 0 )    // check whether num power of 2       &&  (( num & 0xaaaaaaaa ) == 0 ));  // make sure it's power of 2 } 

no loop, no conversion float.