FYI: [PATCH] utimecmp: avoid new GCC 7 warning from -Wbool-operation

[Jim Meyering]

Without this (just pushed) and some other changes, I could not build
coreutils using GCC 7:

From ee54eda045a47253f458e73702bf775eb4a21d4c Mon Sep 17 00:00:00 2001
From: Jim Meyering <meyer...@fb.com>
Date: Wed, 5 Oct 2016 09:13:55 -0700
Subject: [PATCH] utimecmp: avoid new GCC 7 warning from -Wbool-operation
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Testing this module would fail when using GCC 7 like this:
$ CFLAGS='-O -Werror=bool-operation' ./gnulib-tool --create-testdir \
  --dir=/tmp/x --with-tests --test utimecmp
../../gllib/utimecmp.c: In function ‘utimecmp’:
../../gllib/utimecmp.c:291:36: error: ‘~’ on a boolean expression \
  [-Werror=bool-operation]
                 time_t s = src_s & ~ (res == 2 * BILLION);
                                    ^
../../gllib/utimecmp.c:370:16: error: ‘~’ on a boolean expression \
  [-Werror=bool-operation]
       src_s &= ~ (res == 2 * BILLION);
                ^
* lib/utimecmp.c (utimecmp): Do not apply "~" to a boolean.
Instead, make it explicit that we intend to apply it to 0 or 1.
---
 ChangeLog      | 18 ++++++++++++++++++
 lib/utimecmp.c |  4 ++--
 2 files changed, 20 insertions(+), 2 deletions(-)

diff --git a/ChangeLog b/ChangeLog
index 7a3171c..71de7fa 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,21 @@
+2016-10-05  Jim Meyering  <meyer...@fb.com>
+
+       utimecmp: avoid new GCC 7 warning from -Wbool-operation
+       Testing this module would fail when using GCC 7 like this:
+       $ CFLAGS='-O -Werror=bool-operation' ./gnulib-tool --create-testdir \
+         --dir=/tmp/x --with-tests --test utimecmp
+       ../../gllib/utimecmp.c: In function ‘utimecmp’:
+       ../../gllib/utimecmp.c:291:36: error: ‘~’ on a boolean expression \
+         [-Werror=bool-operation]
+                        time_t s = src_s & ~ (res == 2 * BILLION);
+                                           ^
+       ../../gllib/utimecmp.c:370:16: error: ‘~’ on a boolean expression \
+         [-Werror=bool-operation]
+              src_s &= ~ (res == 2 * BILLION);
+                       ^
+       * lib/utimecmp.c (utimecmp): Do not apply "~" to a boolean.
+       Instead, make it explicit that we intend to apply it to 0 or 1.
+
 2016-10-02  Jim Meyering  <meyer...@fb.com>

        vasnprintf.c: avoid spurious warning from GCC 7
diff --git a/lib/utimecmp.c b/lib/utimecmp.c
index ac3d626..c2e3057 100644
--- a/lib/utimecmp.c
+++ b/lib/utimecmp.c
@@ -288,7 +288,7 @@ utimecmp (char const *dst_name,
                  to interrogate the file system to deduce the exact time
                  stamp resolution; return the answer directly.  */
               {
-                time_t s = src_s & ~ (res == 2 * BILLION);
+                time_t s = src_s & ~ (res == 2 * BILLION ? 1 : 0);
                 if (src_s < dst_s || (src_s == dst_s && src_ns <= dst_ns))
                   return 1;
                 if (dst_s < s
@@ -367,7 +367,7 @@ utimecmp (char const *dst_name,
         }

       /* Truncate the source's time stamp according to the resolution.  */
-      src_s &= ~ (res == 2 * BILLION);
+      src_s &= ~ (res == 2 * BILLION ? 1 : 0);
       src_ns -= src_ns % res;
     }

-- 
2.7.4