bitmap: implement bitmap_is_subset()

The bitmap_is_subset() function checks if the 'self' bitmap contains any
bitmaps that are not on in the 'other' bitmap. Up until this patch, it
had a declaration, but no implementation or callers. A subsequent patch
will want this function, so implement it here.

Helped-by: Junio C Hamano <gitster@pobox.com>
Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

ewah/bitmap.c

@@ -195,6 +195,27 @@ int bitmap_equals(struct bitmap *self, struct bitmap *other)
 	return 1;
 }
 
+int bitmap_is_subset(struct bitmap *self, struct bitmap *other)
+{
+	size_t common_size, i;
+
+	if (self->word_alloc < other->word_alloc)
+		common_size = self->word_alloc;
+	else {
+		common_size = other->word_alloc;
+		for (i = common_size; i < self->word_alloc; i++) {
+			if (self->words[i])
+				return 1;
+		}
+	}
+
+	for (i = 0; i < common_size; i++) {
+		if (self->words[i] & ~other->words[i])
+			return 1;
+	}
+	return 0;
+}
+
 void bitmap_reset(struct bitmap *bitmap)
 {
 	memset(bitmap->words, 0x0, bitmap->word_alloc * sizeof(eword_t));

ewah/ewok.h

@@ -180,7 +180,7 @@ int bitmap_get(struct bitmap *self, size_t pos);
 void bitmap_reset(struct bitmap *self);
 void bitmap_free(struct bitmap *self);
 int bitmap_equals(struct bitmap *self, struct bitmap *other);
-int bitmap_is_subset(struct bitmap *self, struct bitmap *super);
+int bitmap_is_subset(struct bitmap *self, struct bitmap *other);
 
 struct ewah_bitmap * bitmap_to_ewah(struct bitmap *bitmap);
 struct bitmap *ewah_to_bitmap(struct ewah_bitmap *ewah);