[v1] tools/nolibc: various new functions

[PATCH 11/15] tools/nolibc: add difftime()

Posted by Thomas Weißschuh 7 months, 3 weeks ago

This is used in various selftests and will be handy when integrating
those with nolibc.

Signed-off-by: Thomas Weißschuh <thomas.weissschuh@linutronix.de>
---
 tools/include/nolibc/time.h                  | 7 +++++++
 tools/testing/selftests/nolibc/nolibc-test.c | 1 +
 2 files changed, 8 insertions(+)

diff --git a/tools/include/nolibc/time.h b/tools/include/nolibc/time.h
index 28a1549adb14e2087fa8fbdb7e9c35e1c3f22c2a..760133c574ece97165e3bba5616a387deaf07aff 100644
--- a/tools/include/nolibc/time.h
+++ b/tools/include/nolibc/time.h
@@ -105,6 +105,13 @@ int clock_settime(clockid_t clockid, struct timespec *tp)
 }
 
 
+static __inline__
+double difftime(time_t time1, time_t time2)
+{
+	return time1 - time2;
+}
+
+
 static __attribute__((unused))
 time_t time(time_t *tptr)
 {
diff --git a/tools/testing/selftests/nolibc/nolibc-test.c b/tools/testing/selftests/nolibc/nolibc-test.c
index aed71de4b4f3dd1f183c7fc25e5a5cee466600ed..fd8bab42e75157967658690005bc9142360fc135 100644
--- a/tools/testing/selftests/nolibc/nolibc-test.c
+++ b/tools/testing/selftests/nolibc/nolibc-test.c
@@ -1423,6 +1423,7 @@ int run_stdlib(int min, int max)
 		CASE_TEST(toupper_noop);            EXPECT_EQ(1, toupper('A'), 'A'); break;
 		CASE_TEST(abs);                     EXPECT_EQ(1, abs(-10), 10); break;
 		CASE_TEST(abs_noop);                EXPECT_EQ(1, abs(10), 10); break;
+		CASE_TEST(difftime);                EXPECT_EQ(1, difftime(200., 100.), 100.); break;
 
 		case __LINE__:
 			return ret; /* must be last */

-- 
2.49.0

Re: [PATCH 11/15] tools/nolibc: add difftime()

Posted by Willy Tarreau 7 months, 3 weeks ago

On Wed, Apr 23, 2025 at 05:01:41PM +0200, Thomas Weißschuh wrote:
> This is used in various selftests and will be handy when integrating
> those with nolibc.
> 
> Signed-off-by: Thomas Weißschuh <thomas.weissschuh@linutronix.de>
> ---
>  tools/include/nolibc/time.h                  | 7 +++++++
>  tools/testing/selftests/nolibc/nolibc-test.c | 1 +
>  2 files changed, 8 insertions(+)
> 
> diff --git a/tools/include/nolibc/time.h b/tools/include/nolibc/time.h
> index 28a1549adb14e2087fa8fbdb7e9c35e1c3f22c2a..760133c574ece97165e3bba5616a387deaf07aff 100644
> --- a/tools/include/nolibc/time.h
> +++ b/tools/include/nolibc/time.h
> @@ -105,6 +105,13 @@ int clock_settime(clockid_t clockid, struct timespec *tp)
>  }
>  
>  
> +static __inline__
> +double difftime(time_t time1, time_t time2)
> +{
> +	return time1 - time2;
> +}

Thanks for making me discover difftime(). I've never heard about it, and
seeing it return a double looks totally weird, but that's how it is indeed.

In case time_t would be unsigned, this would return a large unsigned
value. I think it could be more robust to explicitly cast the two
inputs to long:

	return (long)time1 - (long)time2;

> diff --git a/tools/testing/selftests/nolibc/nolibc-test.c b/tools/testing/selftests/nolibc/nolibc-test.c
> index aed71de4b4f3dd1f183c7fc25e5a5cee466600ed..fd8bab42e75157967658690005bc9142360fc135 100644
> --- a/tools/testing/selftests/nolibc/nolibc-test.c
> +++ b/tools/testing/selftests/nolibc/nolibc-test.c
> @@ -1423,6 +1423,7 @@ int run_stdlib(int min, int max)
>  		CASE_TEST(toupper_noop);            EXPECT_EQ(1, toupper('A'), 'A'); break;
>  		CASE_TEST(abs);                     EXPECT_EQ(1, abs(-10), 10); break;
>  		CASE_TEST(abs_noop);                EXPECT_EQ(1, abs(10), 10); break;
> +		CASE_TEST(difftime);                EXPECT_EQ(1, difftime(200., 100.), 100.); break;

Then here maybe test it in reverse to make sure the types don't cause trouble:

		CASE_TEST(difftime);                EXPECT_EQ(1, difftime(100., 200.), -100.); break;

Willy

Re: [PATCH 11/15] tools/nolibc: add difftime()

Posted by Thomas Weißschuh 7 months, 3 weeks ago

On Sat, Apr 26, 2025 at 12:45:20PM +0200, Willy Tarreau wrote:
> On Wed, Apr 23, 2025 at 05:01:41PM +0200, Thomas Weißschuh wrote:
> > This is used in various selftests and will be handy when integrating
> > those with nolibc.
> > 
> > Signed-off-by: Thomas Weißschuh <thomas.weissschuh@linutronix.de>
> > ---
> >  tools/include/nolibc/time.h                  | 7 +++++++
> >  tools/testing/selftests/nolibc/nolibc-test.c | 1 +
> >  2 files changed, 8 insertions(+)
> > 
> > diff --git a/tools/include/nolibc/time.h b/tools/include/nolibc/time.h
> > index 28a1549adb14e2087fa8fbdb7e9c35e1c3f22c2a..760133c574ece97165e3bba5616a387deaf07aff 100644
> > --- a/tools/include/nolibc/time.h
> > +++ b/tools/include/nolibc/time.h
> > @@ -105,6 +105,13 @@ int clock_settime(clockid_t clockid, struct timespec *tp)
> >  }
> >  
> >  
> > +static __inline__
> > +double difftime(time_t time1, time_t time2)
> > +{
> > +	return time1 - time2;
> > +}
> 
> Thanks for making me discover difftime(). I've never heard about it, and
> seeing it return a double looks totally weird, but that's how it is indeed.
> 
> In case time_t would be unsigned, this would return a large unsigned
> value. I think it could be more robust to explicitly cast the two
> inputs to long:
> 
> 	return (long)time1 - (long)time2;

time_t is explicitly defined as "signed long" in nolibc's std.h.
If we change it at some time in the future we will have to audit any usage site
of time_t in any case.

> > diff --git a/tools/testing/selftests/nolibc/nolibc-test.c b/tools/testing/selftests/nolibc/nolibc-test.c
> > index aed71de4b4f3dd1f183c7fc25e5a5cee466600ed..fd8bab42e75157967658690005bc9142360fc135 100644
> > --- a/tools/testing/selftests/nolibc/nolibc-test.c
> > +++ b/tools/testing/selftests/nolibc/nolibc-test.c
> > @@ -1423,6 +1423,7 @@ int run_stdlib(int min, int max)
> >  		CASE_TEST(toupper_noop);            EXPECT_EQ(1, toupper('A'), 'A'); break;
> >  		CASE_TEST(abs);                     EXPECT_EQ(1, abs(-10), 10); break;
> >  		CASE_TEST(abs_noop);                EXPECT_EQ(1, abs(10), 10); break;
> > +		CASE_TEST(difftime);                EXPECT_EQ(1, difftime(200., 100.), 100.); break;
> 
> Then here maybe test it in reverse to make sure the types don't cause trouble:

Ack.

> 		CASE_TEST(difftime);                EXPECT_EQ(1, difftime(100., 200.), -100.); break;