Davide Libenzi <davidel@xxxxxxxxxxxxxxx> writes:
> Yeah, similar. Mine is below. There's one less branch in the for loops.
Thanks, will apply like this, but I am not sure if you meant windowN or
just window...
-- >8 --
From: Davide Libenzi <davidel@xxxxxxxxxxxxxxx>
Date: Fri, 7 Nov 2008 21:24:33 -0800
Subject: [PATCH] xdiff: give up scanning similar lines early
In a corner case of large files whose lines do not match uniquely, the
loop to eliminate a line that matches multiple locations adjacent to a run
of lines that do not uniquely match wasted too much cycles. Fix this by
giving up early after scanning 100 lines in both direction.
---
xdiff/xprepare.c | 15 +++++++++++++--
1 files changed, 13 insertions(+), 2 deletions(-)
diff --git a/xdiff/xprepare.c b/xdiff/xprepare.c
index e87ab57..6a70cdf 100644
--- a/xdiff/xprepare.c
+++ b/xdiff/xprepare.c
@@ -23,10 +23,9 @@
#include "xinclude.h"
-
#define XDL_KPDIS_RUN 4
#define XDL_MAX_EQLIMIT 1024
-
+#define XDL_SIMSCAN_WINDOWN 100
typedef struct s_xdlclass {
@@ -313,6 +312,18 @@ static int xdl_clean_mmatch(char const *dis, long i, long s, long e) {
long r, rdis0, rpdis0, rdis1, rpdis1;
/*
+ * Limits the window the is examined during the similar-lines
+ * scan. The loops below stops when dis[i - r] == 1 (line that
+ * has no match), but there are corner cases where the loop
+ * proceed all the way to the extremities by causing huge
+ * performance penalties in case of big files.
+ */
+ if (i - s > XDL_SIMSCAN_WINDOWN)
+ s = i - XDL_SIMSCAN_WINDOWN;
+ if (e - i > XDL_SIMSCAN_WINDOWN)
+ e = i + XDL_SIMSCAN_WINDOWN;
+
+ /*
* Scans the lines before 'i' to find a run of lines that either
* have no match (dis[j] == 0) or have multiple matches (dis[j] > 1).
* Note that we always call this function with dis[i] > 1, so the
--
1.6.0.3.674.gdf99f
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