[v2,08/26] ewah: implement `bitmap_is_empty()`

Commit Message

Taylor Blau Dec. 14, 2023, 10:23 p.m. UTC

In a future commit, we will want to check whether or not a bitmap has
any bits set in any of its words. The best way to do this (prior to the
existence of this patch) is to call `bitmap_popcount()` and check
whether the result is non-zero.

But this is semi-wasteful, since we do not need to know the exact number
of bits set, only whether or not there is at least one of them.

Implement a new helper function to check just that.

Suggested-by: Patrick Steinhardt <[e-mail]>
Signed-off-by: Taylor Blau <[e-mail]>
---
 ewah/bitmap.c | 9 +++++++++
 ewah/ewok.h   | 1 +
 2 files changed, 10 insertions(+)

Patch

diff --git a/ewah/bitmap.c b/ewah/bitmap.c
index 7b525b1ecd..ac7e0af622 100644
--- a/ewah/bitmap.c
+++ b/ewah/bitmap.c
@@ -169,6 +169,15 @@  size_t bitmap_popcount(struct bitmap *self)
 	return count;
 }
 
+int bitmap_is_empty(struct bitmap *self)
+{
+	size_t i;
+	for (i = 0; i < self->word_alloc; i++)
+		if (self->words[i])
+			return 0;
+	return 1;
+}
+
 int bitmap_equals(struct bitmap *self, struct bitmap *other)
 {
 	struct bitmap *big, *small;
diff --git a/ewah/ewok.h b/ewah/ewok.h
index 7eb8b9b630..c11d76c6f3 100644
--- a/ewah/ewok.h
+++ b/ewah/ewok.h
@@ -189,5 +189,6 @@  void bitmap_or_ewah(struct bitmap *self, struct ewah_bitmap *other);
 void bitmap_or(struct bitmap *self, const struct bitmap *other);
 
 size_t bitmap_popcount(struct bitmap *self);
+int bitmap_is_empty(struct bitmap *self);
 
 #endif