From ffd63aedad3c0eb08ebb27103e5f242f8732dc0c Mon Sep 17 00:00:00 2001
From: Paul Eggert <eggert@cs.ucla.edu>
Date: Tue, 24 Jul 2018 10:18:28 -0700
Subject: cmp: fix bug in -b diagnostic

Problem reported by mancha (Bug#32249).
* src/cmp.c (count_newlines): Restore old value of sentinel.
* tests/cmp: Test for the bug.
---
 src/cmp.c |  2 ++
 tests/cmp | 10 ++++++++++
 2 files changed, 12 insertions(+)

diff --git a/src/cmp.c b/src/cmp.c
index 04638e3..2811392 100644
--- a/src/cmp.c
+++ b/src/cmp.c
@@ -639,9 +639,11 @@ count_newlines (char *buf, size_t bufsize)
   size_t count = 0;
   char *p;
   char *lim = buf + bufsize;
+  char ch = *lim;
   *lim = '\n';
   for (p = buf; (p = rawmemchr (p, '\n')) != lim; p++)
     count++;
+  *lim = ch;
   return count;
 }
 
diff --git a/tests/cmp b/tests/cmp
index 160c1ea..ca0fe5e 100755
--- a/tests/cmp
+++ b/tests/cmp
@@ -208,4 +208,14 @@ done >out1
 
 compare exp1 out1 || fail=1
 
+printf 'bad\n' >bad
+printf 'bug\n' >bug
+echo LC_ALL=C cmp -b bad bug
+LC_ALL=C cmp -b bad bug
+test $? -eq 1 || fail=1
+case `LC_ALL=C cmp -b bad bug` in
+  'bad bug differ: byte 2, line 1 is '*' a '*' u') ;;
+  *) echo 'expected cmp -b to report a and u'; fail=1;;
+esac
+
 Exit $fail
-- 
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