Am 08.06.19 um 16:42 schrieb Jeff Hostetler via GitGitGadget:
> From: Jeff Hostetler <jeffh...@microsoft.com>
>
> Teach register_rename_src() to see if new file pair
> can simply be appended to the rename_src[] array before
> performing the binary search to find the proper insertion
> point.
>
> This is a performance optimization. This routine is called
> during run_diff_files in status and the caller is iterating
> over the sorted index, so we should expect to be able to
> append in the normal case. The existing insert logic is
> preserved so we don't have to assume that, but simply take
> advantage of it if possible.
>
> Signed-off-by: Jeff Hostetler <jeffh...@microsoft.com>
> Signed-off-by: Johannes Schindelin <johannes.schinde...@gmx.de>
> ---
> diffcore-rename.c | 13 +++++++++++++
> 1 file changed, 13 insertions(+)
>
> diff --git a/diffcore-rename.c b/diffcore-rename.c
> index 07bd34b631..5bfc5f6c22 100644
> --- a/diffcore-rename.c
> +++ b/diffcore-rename.c
> @@ -82,6 +82,18 @@ static struct diff_rename_src *register_rename_src(struct
> diff_filepair *p)
>
> first = 0;
> last = rename_src_nr;
> +
> + if (last > 0) {
> + struct diff_rename_src *src = &(rename_src[last-1]);
> + int cmp = strcmp(one->path, src->p->one->path);
> + if (!cmp)
> + return src;
> + if (cmp > 0) {
> + first = last;
> + goto append_it;
The goto is not necessary from a logical point of view; the binary
search is skipped even without it because the loop condition below is
not met anymore.
> + }
You could decrement "last" at this point as a micro-optimization, to use
all three possible outcomes of the comparison to make some progress.
Not sure if any of that would have a _measurable_ impact, though, so I
don't mind the patch going in as is.
> + }
> +
> while (last > first) {
> int next = (last + first) >> 1;
Hmm, "last" and "first" are ints as well, so this will give weird results
when "last" > INT_MAX / 2. I thought 19716b21a4 ("cleanup: fix possible
overflow errors in binary search", 2017-10-08) got us rid of those, but
git grep -n '(.*+.*) >> 1' actually finds some more cases:
builtin/ls-files.c:376: int next = (last + first) >> 1;
diffcore-rename.c:26: int next = (last + first) >> 1;
diffcore-rename.c:86: int next = (last + first) >> 1;
dir.c:704: int cmp, next = (last + first) >> 1;
name-hash.c:349: int mid = (begin + end) >> 1;
read-cache.c:552: int next = (last + first) >> 1;
sh-i18n--envsubst.c:252: size_t j = (j1 + j2) >> 1;
(Not caused by this patch, of course, just noticed it in the context.)
> struct diff_rename_src *src = &(rename_src[next]);
> @@ -95,6 +107,7 @@ static struct diff_rename_src *register_rename_src(struct
> diff_filepair *p)
> first = next+1;
> }
>
> +append_it:
> /* insert to make it at "first" */
> ALLOC_GROW(rename_src, rename_src_nr + 1, rename_src_alloc);
> rename_src_nr++;
>
Anyway, this here should work as well (and fix the possible overflow),
but may be too terse and quirky:
diff --git a/diffcore-rename.c b/diffcore-rename.c
index 07bd34b631..f2a9007e08 100644
--- a/diffcore-rename.c
+++ b/diffcore-rename.c
@@ -76,14 +76,13 @@ static int rename_src_nr, rename_src_alloc;
static struct diff_rename_src *register_rename_src(struct diff_filepair *p)
{
- int first, last;
+ int first, last, next;
struct diff_filespec *one = p->one;
unsigned short score = p->score;
first = 0;
last = rename_src_nr;
- while (last > first) {
- int next = (last + first) >> 1;
+ for (next = last - 1; last > first; next = first + (last - first) / 2) {
struct diff_rename_src *src = &(rename_src[next]);
int cmp = strcmp(one->path, src->p->one->path);
if (!cmp)
