ARB_FREEIDX
ARB_FREEIDX(ctd32tree) == ARB_SELFIDX(ctd32tree, ctd32) :
ARB_FREEIDX(ctd64tree) == ARB_SELFIDX(ctd64tree, ctd64)),
ARB_NEXTFREEIDX(elm, field) = ARB_FREEIDX(head); \
ARB_FREEIDX(head) = ARB_SELFIDX(head, elm); \
if (ARB_FREEIDX(head) == ARB_NULLIDX && !ARB_FULL(head)) { \
_elm = _prevelm = ARB_NODE(head, ARB_FREEIDX(head)); \
ARB_FREEIDX(head) = \