ewah: implement `bitmap_is_empty()`

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 <ps@pks.im>
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/ewah/bitmap.c b/ewah/bitmap.c
index 7b525b1ecd896e02dfa71cdf3aab75496d998fac..ac7e0af622a8fc74b678b57f464698d1bc9a45e7 100644 (file)
--- 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 7eb8b9b63013daa70c91687108307d38a9eb1e09..c11d76c6f336930e0ea540a5b40c594bdb9f5be2 100644 (file)
--- 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