/* A simple garbage-collected object memory.
 *
 * An object consists of a header word, zero to 255 pointer words, and
 * zero to 255 non-pointer data words, in that order.  Words are 32
 * bits.  The header word consists of a 16-bit class ID, an 8-bit
 * pointer count, and an 8-bit data word count.  The pointers are
 * counted in words relative to the beginning of the object memory,
 * and can thus address up to 16 gigabytes of objects, similar to
 * HotSpot “compressed oops”.  The first word of the object memory is
 * reserved for a special null object, so zero pointers never point to
 * any other object.
 *
 * This structure is designed to make a Cheney-style garbage collector
 * as simple as possible; the collector can merely keep track of which
 * object in tospace is being scanned and what pointer index it’s at.
 * It gives up considerable efficiency by not segregating objects by
 * size and type and by not being generational.
 *
 */