Question

I’m having problems with left bit shifts in Java returning incorrect values…

Take 108 << 60 for instance. The answer should be*:

124515522497539473408

Java is returning this value

-4611686018427387904

for this statement:

System.out.println(108L << 60L);

Why??? Both values are forced longs… so I see no reason why any bit values should be truncated. What am I missing here?

*Citation: Wolfram Alpha

Answer 1

You are shifting beyond the length of a long (64 bits). 108 occupies seven bits, so 108L << 60L requires 67 bits to represent it correctly. Actually, since it’s a signed type, you’d need 68 bits to avoid having it interpreted as a negative number.