From 079fe1dae8504c988c50ce41eba78743d3f588e0 Mon Sep 17 00:00:00 2001
From: Junio C Hamano <gitster@pobox.com>
Date: Sun, 16 Dec 2007 13:49:17 -0800
Subject: [PATCH] Re-re-re-fix common tail optimization

We need to be extra careful recovering the removed common section, so
that we do not break context nor the changed incomplete line (i.e. the
last line that does not end with LF).

Signed-off-by: Junio C Hamano <gitster@pobox.com>
---
 t/t4024-diff-optimize-common.sh | 69 +++++++++++++++++++++++++++++++++
 xdiff-interface.c               |  2 +-
 2 files changed, 70 insertions(+), 1 deletion(-)
 create mode 100755 t/t4024-diff-optimize-common.sh

diff --git a/t/t4024-diff-optimize-common.sh b/t/t4024-diff-optimize-common.sh
new file mode 100755
index 0000000000..20fe87b7dd
--- /dev/null
+++ b/t/t4024-diff-optimize-common.sh
@@ -0,0 +1,69 @@
+#!/bin/sh
+
+test_description='common tail optimization'
+
+. ./test-lib.sh
+
+z=zzzzzzzz ;# 8
+z="$z$z$z$z$z$z$z$z" ;# 64
+z="$z$z$z$z$z$z$z$z" ;# 512
+z="$z$z$z$z" ;# 2048
+z2047=$(expr "$z" : '.\(.*\)') ; #2047
+
+test_expect_success setup '
+
+	echo "a$z2047" >file-a &&
+	echo "b" >file-b &&
+	echo "$z2047" >>file-b &&
+	echo "c$z2047" | tr -d "\012" >file-c &&
+	echo "d" >file-d &&
+	echo "$z2047" | tr -d "\012" >>file-d &&
+
+	git add file-a file-b file-c file-d &&
+
+	echo "A$z2047" >file-a &&
+	echo "B" >file-b &&
+	echo "$z2047" >>file-b &&
+	echo "C$z2047" | tr -d "\012" >file-c &&
+	echo "D" >file-d &&
+	echo "$z2047" | tr -d "\012" >>file-d
+
+'
+
+cat >expect <<\EOF
+diff --git a/file-a b/file-a
+--- a/file-a
++++ b/file-a
+@@ -1 +1 @@
+-aZ
++AZ
+diff --git a/file-b b/file-b
+--- a/file-b
++++ b/file-b
+@@ -1 +1 @@
+-b
++B
+diff --git a/file-c b/file-c
+--- a/file-c
++++ b/file-c
+@@ -1 +1 @@
+-cZ
+\ No newline at end of file
++CZ
+\ No newline at end of file
+diff --git a/file-d b/file-d
+--- a/file-d
++++ b/file-d
+@@ -1 +1 @@
+-d
++D
+EOF
+
+test_expect_success 'diff -U0' '
+
+	git diff -U0 | sed -e "/^index/d" -e "s/$z2047/Z/g" >actual &&
+	diff -u expect actual
+
+'
+
+test_done
diff --git a/xdiff-interface.c b/xdiff-interface.c
index 98b02eda35..9ee877c6f4 100644
--- a/xdiff-interface.c
+++ b/xdiff-interface.c
@@ -121,7 +121,7 @@ static void trim_common_tail(mmfile_t *a, mmfile_t *b, long ctx)
 		bp -= blk;
 	}
 
-	while (recovered < trimmed && ctx)
+	while (recovered < trimmed && 0 <= ctx)
 		if (ap[recovered++] == '\n')
 			ctx--;
 	a->size -= (trimmed - recovered);