Re: [PATCH 3/2] Avoid unnecessary strlen() calls
- From
Shawn O. Pearce <spearce@spearce.org>
- Date
- Mar 20, 2007, 03:40 UTC
- Message-ID
- <20070320034020.GB29145@spearce.org>
- In-Reply-To
- <20070320032947.GA29145@spearce.org>
"Shawn O. Pearce" <spearce@spearce.org> wrote:
> Johannes Schindelin <Johannes.Schindelin@gmx.de> wrote: > > -- snipsnap -- > > [PATCH] xdiff/xutils.c(xdl_hash_record): factor out whitespace handling
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> > --- > > > > Please do not consider this patch _unless_ it is proven to enhance > > the profile statistics substantially. > > This is a massive difference for me.
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> # stock v1.5.1-rc1 > $ for a in 1 2 3 4 5;do /usr/bin/time ../lt-blame blame --incremental HEAD git-gui.sh >/dev/null;done > 6.27 real 5.31 user 0.55 sys > 6.40 real 5.32 user 0.55 sys > 6.33 real 5.33 user 0.53 sys > 6.67 real 5.32 user 0.55 sys > 6.18 real 5.31 user 0.53 sys > > # with the above patch > $ for a in 1 2 3 4 5;do /usr/bin/time ../js-blame blame --incremental HEAD git-gui.sh >/dev/null;done > 3.57 real 2.87 user 0.51 sys > 3.58 real 2.87 user 0.51 sys > 3.53 real 2.86 user 0.52 sys > 3.61 real 2.86 user 0.51 sys > 3.64 real 2.87 user 0.52 sys
DrNick suggested on #git to try flipping the isspace test around. This is a smaller change and generated the same ~3.60 seconds run as Dscho's patch. I like DrNick's version better. ;-)
-->8-- [PATCH] xdiff/xutils.c(xdl_hash_record): factor out whitespace handling
Since in at least one use case, xdl_hash_record() takes over 15% of the CPU time, it makes sense to even micro-optimize it. For many cases, no whitespace special handling is needed, and in these cases we should not even bother to check for whitespace in _every_ iteration of the loop.
Signed-off-by: Johannes Schindelin <Johannes.Schindelin@gmx.de> Signed-off-by: Shawn O. Pearce <spearce@spearce.org> --- xdiff/xutils.c | 2 +- 1 files changed, 1 insertions(+), 1 deletions(-)
diff --git a/xdiff/xutils.c b/xdiff/xutils.c index 3653864..7b1f213 100644 --- a/xdiff/xutils.c +++ b/xdiff/xutils.c @@ -241,7 +241,7 @@ unsigned long xdl_hash_record(char const **data, char const *top, long flags) { char const *ptr = *data; for (; ptr < top && *ptr != '\n'; ptr++) { - if (isspace(*ptr) && (flags & XDF_WHITESPACE_FLAGS)) { + if ((flags & XDF_WHITESPACE_FLAGS) && isspace(*ptr)) { const char *ptr2 = ptr; while (ptr + 1 < top && isspace(ptr[1]) && ptr[1] != '\n')
-- 1.5.1.rc1.595.gd1206 -- Shawn.