Use strbuf for struct xdiff_emit_state's remainder

Continually xreallocing and freeing the remainder member of struct
xdiff_emit_state was a noticeable performance hit.  Use a strbuf
instead.

This yields a decent performance improvement on "git blame" on certain
repositories.  For example, before this commit:

$ time git blame -M -C -C -p --incremental server.c >/dev/null
101.52user 0.17system 1:41.73elapsed 99%CPU (0avgtext+0avgdata 0maxresident)k
0inputs+0outputs (0major+39561minor)pagefaults 0swaps

With this commit:

$ time git blame -M -C -C -p --incremental server.c >/dev/null
80.38user 0.30system 1:20.81elapsed 99%CPU (0avgtext+0avgdata 0maxresident)k
0inputs+0outputs (0major+50979minor)pagefaults 0swaps

Signed-off-by: Brian Downing <bdowning@lavos.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 2 insertions, 2 deletions

diff --git a/xdiff-interface.h b/xdiff-interface.h
index 6f3b361..f6a1ec2 100644
--- a/xdiff-interface.h
+++ b/xdiff-interface.h
@@ -2,6 +2,7 @@
 #define XDIFF_INTERFACE_H
 
 #include "xdiff/xdiff.h"
+#include "strbuf.h"
 
 struct xdiff_emit_state;
 
@@ -9,8 +10,7 @@ typedef void (*xdiff_emit_consume_fn)(void *, char *, unsigned long);
 
 struct xdiff_emit_state {
 	xdiff_emit_consume_fn consume;
-	char *remainder;
-	unsigned long remainder_size;
+	struct strbuf remainder;
 };
 
 int xdi_diff(mmfile_t *mf1, mmfile_t *mf2, xpparam_t const *xpp, xdemitconf_t const *xecfg, xdemitcb_t *ecb);