uintset: add l_uintset_subtract

This subtracts set_b from set_a, and returns the new set.

3 files changed, 41 insertions, 0 deletions

diff --git a/ell/ell.sym b/ell/ell.sym
index 8f4e59d7..f4549219 100644
--- a/ell/ell.sym
+++ b/ell/ell.sym
@@ -537,6 +537,7 @@ global:
 	l_uintset_foreach;
 	l_uintset_clone;
 	l_uintset_intersect;
+	l_uintset_subtract;
 	l_uintset_isempty;
 	l_uintset_size;
 	/* uuid */
diff --git a/ell/uintset.c b/ell/uintset.c
index 863bc560..4837bcf0 100644
--- a/ell/uintset.c
+++ b/ell/uintset.c
@@ -533,6 +533,43 @@ LIB_EXPORT struct l_uintset *l_uintset_intersect(const struct l_uintset *set_a,
 }
 
 /**
+ * l_uintset_subtract:
+ * @set_a: The set of numbers
+ * @set_b: The set of numbers to subtract from set_a
+ *
+ * Subtracts two sets of numbers of an equal base, e.g.:
+ * l_uintset_get_min(set_a) must be equal to l_uintset_get_min(set_b) and
+ * l_uintset_get_max(set_a) must be equal to l_uintset_get_max(set_b)
+ *
+ * Returns: A newly allocated l_uintset containing set_a - set_b
+ */
+LIB_EXPORT struct l_uintset *l_uintset_subtract(const struct l_uintset *set_a,
+						const struct l_uintset *set_b)
+{
+	struct l_uintset *subtraction;
+	uint32_t offset;
+	uint32_t offset_max;
+
+	if (unlikely(!set_a || !set_b))
+		return NULL;
+
+	if (unlikely(set_a->min != set_b->min || set_a->max != set_b->max))
+		return NULL;
+
+	subtraction = l_uintset_new_from_range(set_a->min, set_a->max);
+
+	offset_max = (set_a->size + BITS_PER_LONG - 1) / BITS_PER_LONG;
+
+	/* Subtract by: set_a & ~set_b */
+	for (offset = 0; offset < offset_max; offset++) {
+		subtraction->bits[offset] =
+				set_a->bits[offset] & ~(set_b->bits[offset]);
+	}
+
+	return subtraction;
+}
+
+/**
  * l_uintset_isempty
  * @set: The set of numbers
  *
diff --git a/ell/uintset.h b/ell/uintset.h
index aa9de48d..86ce8f7b 100644
--- a/ell/uintset.h
+++ b/ell/uintset.h
@@ -60,6 +60,9 @@ void l_uintset_foreach(const struct l_uintset *set,
 struct l_uintset *l_uintset_clone(const struct l_uintset *original);
 struct l_uintset *l_uintset_intersect(const struct l_uintset *set_a,
 						const struct l_uintset *set_b);
+struct l_uintset *l_uintset_subtract(const struct l_uintset *set_a,
+						const struct l_uintset *set_b);
+
 bool l_uintset_isempty(const struct l_uintset *set);
 uint32_t l_uintset_size(const struct l_uintset *set);