Dubious diff using --diff-algorithm=histogram
- From
- Alejandro Colomar <alx.manpages@gmail.com>
- Date
- Apr 4, 2023, 19:51 UTC
- Message-ID
- <a0b6d751-25fd-a132-f8a5-9844e5d9b8a6@gmail.com>
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
---
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..92bdfb1f 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: - if (nxt_slow_path(end - p < 10)) { - 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..92bdfb1f 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; } alx@asus5775:~/src/nginx/unit/space$ git diff --diff-algorithm=myers diff --git a/src/nxt_http_parse.c b/src/nxt_http_parse.c index 8646a6ce..92bdfb1f 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: - if (nxt_slow_path(end - p < 10)) { - p++; + if (nxt_slow_path(end - p < 10)) { + if (p == end) { return NXT_AGAIN; } alx@asus5775:~/src/nginx/unit/space$ git diff --diff-algorithm=minimal diff --git a/src/nxt_http_parse.c b/src/nxt_http_parse.c index 8646a6ce..92bdfb1f 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: - if (nxt_slow_path(end - p < 10)) { - p++; + if (nxt_slow_path(end - p < 10)) { + if (p == end) { return NXT_AGAIN; }
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