+#define BITMAP_HEADWORDS(_nbits) \
+ ((_nbits) / BITMAP_WORD_BITS)
+#define BITMAP_HEADBYTES(_nbits) \
+ (BITMAP_HEADWORDS(_nbits) * sizeof(bitmap_word))
+
+#define BITMAP_TAILWORD(_bm, _nbits) \
+ ((_bm)[BITMAP_HEADWORDS(_nbits)].w)
+#define BITMAP_HASTAIL(_nbits) (((_nbits) % BITMAP_WORD_BITS) != 0)
+#define BITMAP_TAILBITS(_nbits) \
+ (bitmap_bswap(~(-1UL >> ((_nbits) % BITMAP_WORD_BITS))))
+#define BITMAP_TAIL(_bm, _nbits) \
+ (BITMAP_TAILWORD(_bm, _nbits) & BITMAP_TAILBITS(_nbits))