Does anyone know of good tutorials or even a good book to master bit-level operations? I mean it's almost clear what every operation does (in Java for instance) or where to find the right documentation, but I'm very new to this topic and I wonder how things like:
// Find a power of 2 >= initialCapacity
int capacity = 1;
while (capacity < initialCapacity)
capacity <<= 1;
work (copied from HashMap). I can't imagine how Integers, Longs or whatever data type are affected by bit operations :-(
I mean I don't want to know every kind of operation, just what seems to be fundamental to high level programmers in Java or Scala like the example provided.
Another example would be:
/**
* Applies a supplemental hash function to a given hashCode, which
* defends against poor quality hash functions. This is critical
* because HashMap uses power-of-two length hash tables, that
* otherwise encounter collisions for hashCodes that do not differ
* in lower bits. Note: Null keys always map to hash 0, thus index 0.
*/
static int hash(int h) {
// This function ensures that hashCodes that differ only by
// constant multiples at each bit position have a bounded
// number of collisions (approximately 8 at default load factor).
h ^= (h >>> 20) ^ (h >>> 12);
return h ^ (h >>> 7) ^ (h >>> 4);
}
That just seems to be magic :(
To understand the basics, you need to understand how data is represented. This requires understanding binary and usually two's complement.
Once you understand the basics, a lot of useful hacks can be found at the ubiquitous Stanford source.