[PATCH 1/2] include: sbi_bitmap: add bitmap_empty() function

[Yu-Chien Peter Lin]

Add bitmap_empty() to check if bitmap has no bits set.

Unlike bitmap_weight() which calls sbi_popcount() on every word,
bitmap_empty() uses simple non-zero comparisons with early exit.

Signed-off-by: Yu-Chien Peter Lin <peter.lin at sifive.com>
---
 include/sbi/sbi_bitmap.h | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/include/sbi/sbi_bitmap.h b/include/sbi/sbi_bitmap.h
index 596bcc7d..80d3fe3b 100644
--- a/include/sbi/sbi_bitmap.h
+++ b/include/sbi/sbi_bitmap.h
@@ -143,4 +143,20 @@ static inline int bitmap_weight(const unsigned long *src, int nbits)
 	return res;
 }
 
+static inline bool bitmap_empty(const unsigned long *src, int nbits)
+{
+	if (nbits == 0)
+		return true;
+
+	if (small_const_nbits(nbits))
+		return !(*src & BITMAP_LAST_WORD_MASK(nbits));
+	else {
+		size_t i, len = BITS_TO_LONGS(nbits);
+		for (i = 0; i < len - 1; i++)
+			if (src[i])
+				return false;
+		return !(src[len - 1] & BITMAP_LAST_WORD_MASK(nbits));
+	}
+}
+
 #endif
-- 
2.53.0