threads / patch / 42880

patchuse strbuf_addbuf() for appending a strbuf to another

Subject: [PATCH] use strbuf_addbuf() for appending a strbuf to another

## tl;dr

5 messages between Jul 19, 2016 and Jul 22, 2016. Diffs are folded; open one to read it.

replies: 4people: 3as markdown or json

René Scharfe· Jul 19, 2016, 18:36 UTC · lore
Use strbuf_addbuf() where possible; it's shorter and more efficient.
Signed-off-by: Rene Scharfe <l.s.r@web.de>
---
 dir.c       | 2 +-
 path.c      | 2 +-
 wt-status.c | 2 +-
 3 files changed, 3 insertions(+), 3 deletions(-)
Show changes to 3 files +3 −3

dir.c, path.c, wt-status.c

diff --git a/dir.c b/dir.c
index 6172b34..0ea235f 100644
--- a/dir.c
+++ b/dir.c
@@ -2364,7 +2364,7 @@ void write_untracked_extension(struct strbuf *out, struct untracked_cache *untra
 
 	varint_len = encode_varint(untracked->ident.len, varbuf);
 	strbuf_add(out, varbuf, varint_len);
-	strbuf_add(out, untracked->ident.buf, untracked->ident.len);
+	strbuf_addbuf(out, &untracked->ident);
 
 	strbuf_add(out, ouc, ouc_size(len));
 	free(ouc);
diff --git a/path.c b/path.c
index 259aeed..17551c4 100644
--- a/path.c
+++ b/path.c
@@ -483,7 +483,7 @@ static void do_submodule_path(struct strbuf *buf, const char *path,
 		strbuf_addstr(buf, git_dir);
 	}
 	strbuf_addch(buf, '/');
-	strbuf_addstr(&git_submodule_dir, buf->buf);
+	strbuf_addbuf(&git_submodule_dir, buf);
 
 	strbuf_vaddf(buf, fmt, args);
 
diff --git a/wt-status.c b/wt-status.c
index c19b52c..dbdb543 100644
--- a/wt-status.c
+++ b/wt-status.c
@@ -1062,7 +1062,7 @@ static void abbrev_sha1_in_line(struct strbuf *line)
 			strbuf_addf(split[1], "%s ", abbrev);
 			strbuf_reset(line);
 			for (i = 0; split[i]; i++)
-				strbuf_addf(line, "%s", split[i]->buf);
+				strbuf_addbuf(line, split[i]);
 		}
 	}
 	strbuf_list_free(split);

-- 
2.9.2
Jeff King· Jul 20, 2016, 13:20 UTC · re: René Scharfe · lore

Re: [PATCH] use strbuf_addbuf() for appending a strbuf to another

On Tue, Jul 19, 2016 at 08:36:29PM +0200, René Scharfe wrote:
> Use strbuf_addbuf() where possible; it's shorter and more efficient.
After seeing "efficient", I was momentarily surprised by the first hunk:
Show 10 quoted lines
> diff --git a/dir.c b/dir.c
> index 6172b34..0ea235f 100644
> --- a/dir.c
> +++ b/dir.c
> @@ -2364,7 +2364,7 @@ void write_untracked_extension(struct strbuf *out, struct untracked_cache *untra
>  
>  	varint_len = encode_varint(untracked->ident.len, varbuf);
>  	strbuf_add(out, varbuf, varint_len);
> -	strbuf_add(out, untracked->ident.buf, untracked->ident.len);
> +	strbuf_addbuf(out, &untracked->ident);

This is actually slightly _less_ efficient, because we already are using the precomputed len, and the new code will call an extra strbuf_grow() to cover the case where the two arguments are the same. See 81d2cae (strbuf_addbuf(): allow passing the same buf to dst and src, 2010-01-12).

But it almost certainly doesn't matter, and it definitely _is_ an improvement for the other "addstr" cases, which are doing an unncessary strlen().

And anyway the readability improvement trumps all of that in my mind. So I think overall it is a nice cleanup; I'm mostly just commenting for the sake of other reviewers.

-Peff
René Scharfe· Jul 21, 2016, 16:46 UTC · re: Jeff King · lore

Re: [PATCH] use strbuf_addbuf() for appending a strbuf to another

Am 20.07.2016 um 15:20 schrieb Jeff King:
Show 22 quoted lines
> On Tue, Jul 19, 2016 at 08:36:29PM +0200, René Scharfe wrote:
> 
>> Use strbuf_addbuf() where possible; it's shorter and more efficient.
> 
> After seeing "efficient", I was momentarily surprised by the first hunk:
> 
>> diff --git a/dir.c b/dir.c
>> index 6172b34..0ea235f 100644
>> --- a/dir.c
>> +++ b/dir.c
>> @@ -2364,7 +2364,7 @@ void write_untracked_extension(struct strbuf *out, struct untracked_cache *untra
>>   
>>   	varint_len = encode_varint(untracked->ident.len, varbuf);
>>   	strbuf_add(out, varbuf, varint_len);
>> -	strbuf_add(out, untracked->ident.buf, untracked->ident.len);
>> +	strbuf_addbuf(out, &untracked->ident);
> 
> This is actually slightly _less_ efficient, because we already are using
> the precomputed len, and the new code will call an extra strbuf_grow()
> to cover the case where the two arguments are the same.  See 81d2cae
> (strbuf_addbuf(): allow passing the same buf to dst and src,
> 2010-01-12).

Ah, I wasn't aware of that. Calling strbuf_grow() twice shouldn't be thaaat bad. However, I wonder where we duplicate strbufs, or why we would ever want to do so. Anyway, here's a patch for that:

-- >8 --
Subject: strbuf: avoid calling strbuf_grow() twice in strbuf_addbuf()

Implement strbuf_addbuf() as a normal function in order to avoid calling strbuf_grow() twice, with the second callinside strbud_add() being a no-op. This is slightly faster and also reduces the text size a bit.

Signed-off-by: Rene Scharfe <l.s.r@web.de>
---
 strbuf.c | 7 +++++++
 strbuf.h | 6 +-----
 2 files changed, 8 insertions(+), 5 deletions(-)
Show changes to 2 files +8 −5

strbuf.c, strbuf.h

diff --git a/strbuf.c b/strbuf.c
index 1ba600b..f3bd571 100644
--- a/strbuf.c
+++ b/strbuf.c
@@ -197,6 +197,13 @@ void strbuf_add(struct strbuf *sb, const void *data, size_t len)
 	strbuf_setlen(sb, sb->len + len);
 }
 
+void strbuf_addbuf(struct strbuf *sb, const struct strbuf *sb2)
+{
+	strbuf_grow(sb, sb2->len);
+	memcpy(sb->buf + sb->len, sb2->buf, sb2->len);
+	strbuf_setlen(sb, sb->len + sb2->len);
+}
+
 void strbuf_adddup(struct strbuf *sb, size_t pos, size_t len)
 {
 	strbuf_grow(sb, len);
diff --git a/strbuf.h b/strbuf.h
index 83c5c98..ba8d5f1 100644
--- a/strbuf.h
+++ b/strbuf.h
@@ -263,11 +263,7 @@ static inline void strbuf_addstr(struct strbuf *sb, const char *s)
 /**
  * Copy the contents of another buffer at the end of the current one.
  */
-static inline void strbuf_addbuf(struct strbuf *sb, const struct strbuf *sb2)
-{
-	strbuf_grow(sb, sb2->len);
-	strbuf_add(sb, sb2->buf, sb2->len);
-}
+extern void strbuf_addbuf(struct strbuf *sb, const struct strbuf *sb2);
 
 /**
  * Copy part of the buffer from a given position till a given length to the

-- 
2.9.2
Jeff King· Jul 21, 2016, 21:02 UTC · re: René Scharfe · lore

Re: [PATCH] use strbuf_addbuf() for appending a strbuf to another

On Thu, Jul 21, 2016 at 06:46:44PM +0200, René Scharfe wrote:
Show 12 quoted lines
> >> -	strbuf_add(out, untracked->ident.buf, untracked->ident.len);
> >> +	strbuf_addbuf(out, &untracked->ident);
> > 
> > This is actually slightly _less_ efficient, because we already are using
> > the precomputed len, and the new code will call an extra strbuf_grow()
> > to cover the case where the two arguments are the same.  See 81d2cae
> > (strbuf_addbuf(): allow passing the same buf to dst and src,
> > 2010-01-12).
> 
> Ah, I wasn't aware of that.  Calling strbuf_grow() twice shouldn't be
> thaaat bad.  However, I wonder where we duplicate strbufs, or why we
> would ever want to do so.  Anyway, here's a patch for that:
I don't think we do. Going back to the original discussion:
  http://thread.gmane.org/gmane.comp.version-control.git/136141/focus=136774

it was mostly just "hey, this would fail really confusingly if we ever did, so let's make it safe".

The second strbuf_grow() is by definition a noop (which is why 81d2cae works at all), but we do pay the size-computation cost.

Show 6 quoted lines
> -- >8 --
> Subject: strbuf: avoid calling strbuf_grow() twice in strbuf_addbuf()
> 
> Implement strbuf_addbuf() as a normal function in order to avoid calling
> strbuf_grow() twice, with the second callinside strbud_add() being a
> no-op.  This is slightly faster and also reduces the text size a bit.

Seems reasonable. IMHO the main advantage is that one does not have to reason about the double strbuf_grow() (i.e., that the strbuf_add() is safe because we know its grow is a noop).

-Peff
Junio C Hamano· Jul 22, 2016, 16:22 UTC · re: Jeff King · lore

Re: [PATCH] use strbuf_addbuf() for appending a strbuf to another

Jeff King <peff@peff.net> writes:
Show 9 quoted lines
> I don't think we do. Going back to the original discussion:
>
>   http://thread.gmane.org/gmane.comp.version-control.git/136141/focus=136774
>
> it was mostly just "hey, this would fail really confusingly if we ever
> did, so let's make it safe".
>
> The second strbuf_grow() is by definition a noop (which is why 81d2cae
> works at all), but we do pay the size-computation cost.

Both true. If the second one is not a noop, nothing is fixed by 81d2cae at all, but it is subtle.

René's update makes it far easier to understand what is going on.
Show 12 quoted lines
>> -- >8 --
>> Subject: strbuf: avoid calling strbuf_grow() twice in strbuf_addbuf()
>> 
>> Implement strbuf_addbuf() as a normal function in order to avoid calling
>> strbuf_grow() twice, with the second callinside strbud_add() being a
>> no-op.  This is slightly faster and also reduces the text size a bit.
>
> Seems reasonable.  IMHO the main advantage is that one does not have to
> reason about the double strbuf_grow() (i.e., that the strbuf_add() is
> safe because we know its grow is a noop).
>
> -Peff

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