diff mbox series

[v3,3/9] ewah/bitmap: introduce bitmap_word_alloc()

Message ID 20191115141541.11149-4-chriscool@tuxfamily.org (mailing list archive)
State New, archived
Headers show
Series Rewrite packfile reuse code | expand

Commit Message

Christian Couder Nov. 15, 2019, 2:15 p.m. UTC 
From: Jeff King <peff@peff.net>

In a following commit we will need to allocate a variable
number of bitmap words, instead of always 32, so let's add
bitmap_word_alloc() for this purpose.

Helped-by: Jonathan Tan <jonathantanmy@google.com>
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Christian Couder <chriscool@tuxfamily.org>
---
 ewah/bitmap.c | 13 +++++++++----
 ewah/ewok.h   |  1 +
 2 files changed, 10 insertions(+), 4 deletions(-)

Comments

Jeff King Dec. 9, 2019, 6:28 a.m. UTC | #1 
On Fri, Nov 15, 2019 at 03:15:35PM +0100, Christian Couder wrote:

> In a following commit we will need to allocate a variable
> number of bitmap words, instead of always 32, so let's add
> bitmap_word_alloc() for this purpose.

This name is much better than the horrible "bitmap_new2()" it was called
in the original. ;)

I wonder if "new_with_world_alloc" or "new_with_size" would make it more
obvious that this is also a constructor, though.

>  void bitmap_set(struct bitmap *self, size_t pos)
>  {
>  	size_t block = EWAH_BLOCK(pos);
>  
>  	if (block >= self->word_alloc) {
>  		size_t old_size = self->word_alloc;
> -		self->word_alloc = block * 2;
> +		self->word_alloc = block ? block * 2 : 1;

Since this hunk caused so much confusion, maybe worth calling it out in
the commit message. Something like:

  Note that we have to adjust the block growth in bitmap_set(), since
  a caller could now use an initial size of "0" (we don't plan to do
  that, but it doesn't hurt to be defensive).

-Peff
Christian Couder Dec. 11, 2019, 1:50 p.m. UTC | #2 
On Mon, Dec 9, 2019 at 7:28 AM Jeff King <peff@peff.net> wrote:
>
> On Fri, Nov 15, 2019 at 03:15:35PM +0100, Christian Couder wrote:
>
> > In a following commit we will need to allocate a variable
> > number of bitmap words, instead of always 32, so let's add
> > bitmap_word_alloc() for this purpose.
>
> This name is much better than the horrible "bitmap_new2()" it was called
> in the original. ;)
>
> I wonder if "new_with_world_alloc" or "new_with_size" would make it more
> obvious that this is also a constructor, though.

bitmap_new_with_word_alloc() feels a bit verbose to me for such a
short function, so for now I kept bitmap_word_alloc().

I think that if we really want to use "new" for constructors then a
better solution would be something like renaming bitmap_new(void) to
bitmap_new_default(void) and bitmap_word_alloc(size_t word_alloc) to
bitmap_new(size_t word_alloc).

> >  void bitmap_set(struct bitmap *self, size_t pos)
> >  {
> >       size_t block = EWAH_BLOCK(pos);
> >
> >       if (block >= self->word_alloc) {
> >               size_t old_size = self->word_alloc;
> > -             self->word_alloc = block * 2;
> > +             self->word_alloc = block ? block * 2 : 1;
>
> Since this hunk caused so much confusion, maybe worth calling it out in
> the commit message. Something like:
>
>   Note that we have to adjust the block growth in bitmap_set(), since
>   a caller could now use an initial size of "0" (we don't plan to do
>   that, but it doesn't hurt to be defensive).

Ok, I added the above as a commit message note in my current version.
Jeff King Dec. 12, 2019, 5:45 a.m. UTC | #3 
On Wed, Dec 11, 2019 at 02:50:40PM +0100, Christian Couder wrote:

> > I wonder if "new_with_world_alloc" or "new_with_size" would make it more
> > obvious that this is also a constructor, though.
> 
> bitmap_new_with_word_alloc() feels a bit verbose to me for such a
> short function, so for now I kept bitmap_word_alloc().

OK, that's fine with me...

> I think that if we really want to use "new" for constructors then a
> better solution would be something like renaming bitmap_new(void) to
> bitmap_new_default(void) and bitmap_word_alloc(size_t word_alloc) to
> bitmap_new(size_t word_alloc).

...but that also would be fine with me.

-Peff
diff mbox series

Patch

diff --git a/ewah/bitmap.c b/ewah/bitmap.c
index 52f1178db4..b5fed9621f 100644
--- a/ewah/bitmap.c
+++ b/ewah/bitmap.c
@@ -22,21 +22,26 @@ 
 #define EWAH_MASK(x) ((eword_t)1 << (x % BITS_IN_EWORD))
 #define EWAH_BLOCK(x) (x / BITS_IN_EWORD)
 
-struct bitmap *bitmap_new(void)
+struct bitmap *bitmap_word_alloc(size_t word_alloc)
 {
 	struct bitmap *bitmap = xmalloc(sizeof(struct bitmap));
-	bitmap->words = xcalloc(32, sizeof(eword_t));
-	bitmap->word_alloc = 32;
+	bitmap->words = xcalloc(word_alloc, sizeof(eword_t));
+	bitmap->word_alloc = word_alloc;
 	return bitmap;
 }
 
+struct bitmap *bitmap_new(void)
+{
+	return bitmap_word_alloc(32);
+}
+
 void bitmap_set(struct bitmap *self, size_t pos)
 {
 	size_t block = EWAH_BLOCK(pos);
 
 	if (block >= self->word_alloc) {
 		size_t old_size = self->word_alloc;
-		self->word_alloc = block * 2;
+		self->word_alloc = block ? block * 2 : 1;
 		REALLOC_ARRAY(self->words, self->word_alloc);
 		memset(self->words + old_size, 0x0,
 			(self->word_alloc - old_size) * sizeof(eword_t));
diff --git a/ewah/ewok.h b/ewah/ewok.h
index 84b2a29faa..1b98b57c8b 100644
--- a/ewah/ewok.h
+++ b/ewah/ewok.h
@@ -172,6 +172,7 @@  struct bitmap {
 };
 
 struct bitmap *bitmap_new(void);
+struct bitmap *bitmap_word_alloc(size_t word_alloc);
 void bitmap_set(struct bitmap *self, size_t pos);
 int bitmap_get(struct bitmap *self, size_t pos);
 void bitmap_reset(struct bitmap *self);