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

From: Junio C Hamano <gitster@pobox.com>
Date: Jul 22, 2016, 16:22 UTC
Message-ID: <xmqqr3albq2s.fsf@gitster.mtv.corp.google.com>
In-Reply-To: <20160721210253.GA4604@sigill.intra.peff.net>

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