masking : Java Glossary

You need skill with the various bit operators to pack several fields into a single int and then unpack them again. You do this work with >>>, <<, &, | and ~ . Rarely you might use the signed shift operator >>. For example to extract the low order three bits you mask with binary 00000111, e.g. z = x & 0x07 . To extract bits 4 and 5 you shift and mask, e.g. z = x >>> 4 & 0x03 . To put together a 2-bit x field in bits 4 and 5 and a 3-bit y field in bits 0, 1, 2 you use code like this: z = x << 4 | y . To zero out a the x field you would take the mask for bits 4 and 5, binary 110000, and invert it, and then mask with that, e.g. z &= ~0x30;

Simple Masking

Shift Masking

Combining Fields

// To put together a 2-bit x field in bits 4 and 5
// and a 3-bit y field in low order bits 0, 1, 2 you use code like this:
long z = ( x << 3 ) | y;

Creating Masks Dynamically

Bit Testing

IP Tricks

BitSet