bitset: add next_clear_bit() to find the next clear bit

include/bitset.h

@@ -7,3 +7,4 @@ int is_bit_set(uint8_t *set, size_t n);
 void set_bit(uint8_t *set, size_t n);
 void clear_bit(uint8_t *set, size_t n);
 size_t next_set_bit(uint8_t *set, size_t len);
+size_t next_clear_bit(uint8_t *set, size_t len);

source/bitset.c

@@ -42,3 +42,15 @@ size_t next_set_bit(uint8_t *set, size_t len)
 
 	return SIZE_MAX;
 }
+
+size_t next_clear_bit(uint8_t *set, size_t len)
+{
+	size_t n;
+
+	for (n = 0; n < len; ++n) {
+		if (!is_bit_set(set, n))
+			return n;
+	}
+
+	return SIZE_MAX;
+}