Judy is a C library that provides a state-of-the-art core technology
that implements a sparse dynamic array. Judy arrays are declared
simply with a null pointer. A Judy array consumes memory only when it
is populated, yet can grow to take advantage of all available memory
if desired. Judy's key benefits are scalability, high performance, and
memory efficiency. A Judy array is extensible and can scale up to a
very large number of elements, bounded only by machine memory. Since
Judy is designed as an unbounded array, the size of a Judy array is
not pre-allocated but grows and shrinks dynamically with the array
population.