WHITEBITS
#define maskcolors (~(bit2mask(BLACKBIT, OLDBIT) | WHITEBITS))
#define white2gray(x) resetbits(gch(x)->marked, WHITEBITS)
g->currentwhite = WHITEBITS; /* this "white" makes all objects look dead */
(!testbits((x)->gch.marked, WHITEBITS | bitmask(BLACKBIT)))
#define otherwhite(g) (g->currentwhite ^ WHITEBITS)
#define isdeadm(ow,m) (!(((m) ^ WHITEBITS) & (ow)))
#define changewhite(x) ((x)->gch.marked ^= WHITEBITS)
#define luaC_white(g) cast(lu_byte, (g)->currentwhite & WHITEBITS)
#define iswhite(x) testbits((x)->gch.marked, WHITEBITS)