Re: Dubious diff using --diff-algorithm=histogram
On 4/4/23 21:51, Alejandro Colomar wrote:
Show 17 quoted lines
> Hi,
>
> I've met some strange diff with the histogram algorithm. I know this
> has a lot of magic in it, and it's probably not so trivial to improve,
> and maybe my code base is so weird that it makes the histogram do crazy
> stuff, but I wanted to show it to you in case there's anything that can
> be improved.
>
> So, patience is showing a better diff than histogram, which shouldn't
> happen usually, and less in this case, where p++ is such a common thing
> to do (although maybe this nxt_slow_path() macro is called a lot in the
> file and confuses the histogram?).
>
> Code base: <https://github.com/nginx/unit.git>
>
> Cheers,
> Alex
Now this has surprised me even more:
alx@asus5775:~/src/nginx/unit/space$ git diff --diff-algorithm=histogram
diff --git a/src/nxt_http_parse.c b/src/nxt_http_parse.c
index 8646a6ce..3559f2e2 100644
--- a/src/nxt_http_parse.c
+++ b/src/nxt_http_parse.c
@@ -340,9 +340,9 @@ nxt_http_parse_request_line(nxt_http_request_parse_t *rp, u_char **pos,
space_after_target:
- if (nxt_slow_path(end - p < 10)) {
+ p++;
- p++;
+ if (nxt_slow_path(end - p < 10)) {
if (p == end) {
return NXT_AGAIN;
alx@asus5775:~/src/nginx/unit/space$ git diff --diff-algorithm=patience
diff --git a/src/nxt_http_parse.c b/src/nxt_http_parse.c
index 8646a6ce..3559f2e2 100644
--- a/src/nxt_http_parse.c
+++ b/src/nxt_http_parse.c
@@ -340,10 +340,10 @@ nxt_http_parse_request_line(nxt_http_request_parse_t *rp, u_char **pos,
space_after_target:
+ p++;
+
if (nxt_slow_path(end - p < 10)) {
- p++;
-
if (p == end) {
return NXT_AGAIN;
}
--
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