[PATCH 3/9] test-date: add a subcommand to measure times in shell scripts

[Johannes Schindelin via GitGitGadget]

From: Johannes Schindelin <johannes.schinde...@gmx.de>

In the next commit, we want to teach Git's test suite to optionally
output test results in JUnit-style .xml files. These files contain
information about the time spent. So we need a way to measure time.

While we could use `date +%s` for that, this will give us only seconds,
i.e. very coarse-grained timings.

GNU `date` supports `date +%s.%N` (i.e. nanosecond-precision output),
but there is no equivalent in BSD `date` (read: on macOS, we would not
be able to obtain precise timings).

So let's introduce `test-tool date getnanos`, with an optional start
time, that outputs preciser values.

Granted, it is a bit pointless to try measuring times accurately in
shell scripts, certainly to nanosecond precision. But it is better than
second-granularity.

Signed-off-by: Johannes Schindelin <johannes.schinde...@gmx.de>
---
 t/helper/test-date.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/t/helper/test-date.c b/t/helper/test-date.c
index a0837371ab..792a805374 100644
--- a/t/helper/test-date.c
+++ b/t/helper/test-date.c
@@ -7,6 +7,7 @@ static const char *usage_msg = "\n"
 "  test-tool date parse [date]...\n"
 "  test-tool date approxidate [date]...\n"
 "  test-tool date timestamp [date]...\n"
+"  test-tool date getnanos [start-nanos]\n"
 "  test-tool date is64bit\n"
 "  test-tool date time_t-is64bit\n";
 
@@ -82,6 +83,15 @@ static void parse_approx_timestamp(const char **argv, struct 
timeval *now)
        }
 }
 
+static void getnanos(const char **argv, struct timeval *now)
+{
+       double seconds = getnanotime() / 1.0e9;
+
+       if (*argv)
+               seconds -= strtod(*argv, NULL);
+       printf("%lf\n", seconds);
+}
+
 int cmd__date(int argc, const char **argv)
 {
        struct timeval now;
@@ -108,6 +118,8 @@ int cmd__date(int argc, const char **argv)
                parse_approxidate(argv+1, &now);
        else if (!strcmp(*argv, "timestamp"))
                parse_approx_timestamp(argv+1, &now);
+       else if (!strcmp(*argv, "getnanos"))
+               getnanos(argv+1, &now);
        else if (!strcmp(*argv, "is64bit"))
                return sizeof(timestamp_t) == 8 ? 0 : 1;
        else if (!strcmp(*argv, "time_t-is64bit"))
-- 
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