# Re: [PATCH] use DIV_ROUND_UP

*Date*: Sun, 9 Jul 2017 16:01:39 +0200
*From*: René Scharfe <l.s.r@xxxxxx>
*Subject*: Re: [PATCH] use DIV_ROUND_UP

Am 09.07.2017 um 15:25 schrieb Martin Ågren:
> On 8 July 2017 at 12:35, René Scharfe <l.s.r@xxxxxx> wrote:
>> Convert code that divides and rounds up to use DIV_ROUND_UP to make the
>> intent clearer and reduce the number of magic constants.
> ...
>> diff --git a/sha1_name.c b/sha1_name.c
>> index e7f7b12ceb..8c513dbff6 100644
>> --- a/sha1_name.c
>> +++ b/sha1_name.c
>> @@ -492,7 +492,7 @@ int find_unique_abbrev_r(char *hex, const unsigned char *sha1, int len)
>> * together we need to divide by 2; but we also want to round
>> * odd numbers up, hence adding one before dividing.
>> */
>> - len = (len + 1) / 2;
>> + len = DIV_ROUND_UP(len, 2);
>
> Since the addition is now an implementation detail of DIV_ROUND_UP,
> should the comment be adjusted, maybe simply by removing ", hence
> adding one before dividing"?
>
> Or perhaps even better, "... divide by 2; but since len might be odd,
> we need to make sure we round up as we divide". My thinking being,
> we're not actually rounding odd numbers up (presumably to even
> numbers), but we're rounding the result of the division up (to the
> smallest larger integer).
Good point; perhaps just squash this in?
---
sha1_name.c | 3 +--
1 file changed, 1 insertion(+), 2 deletions(-)
diff --git a/sha1_name.c b/sha1_name.c
index 8c513dbff6..74fcb6d788 100644
--- a/sha1_name.c
+++ b/sha1_name.c
@@ -489,8 +489,7 @@ int find_unique_abbrev_r(char *hex, const unsigned char *sha1, int len)
* We now know we have on the order of 2^len objects, which
* expects a collision at 2^(len/2). But we also care about hex
* chars, not bits, and there are 4 bits per hex. So all
- * together we need to divide by 2; but we also want to round
- * odd numbers up, hence adding one before dividing.
+ * together we need to divide by 2 and round up.
*/
len = DIV_ROUND_UP(len, 2);
/*
--
2.13.2