commit 41cb26c1696b2e91f6ffe28c98ab471b925de9e8 Author: Nick Mathewson <nickm@torproject.org> Date: Thu Jun 16 10:16:04 2016 -0400 Correct the rounding behavior on tv_mdiff. Fix for bug 19428. --- changes/bug19428 | 5 +++++ src/common/util.c | 12 +++++++++--- src/test/test_util.c | 4 ++-- 3 files changed, 16 insertions(+), 5 deletions(-) diff --git a/changes/bug19428 b/changes/bug19428 new file mode 100644 index 0000000..32d293e --- /dev/null +++ b/changes/bug19428 @@ -0,0 +1,5 @@ + - Minor bugfixes (timing): + o When computing the difference between two times in milliseconds, + we now round to the nearest millisecond correctly. Previously, + we could sometimes round in the wrong direction. Fixes bug 19428; + bugfix on 0.2.2.2-alpha. diff --git a/src/common/util.c b/src/common/util.c index 2a3aec5..d005dad 100644 --- a/src/common/util.c +++ b/src/common/util.c @@ -1386,7 +1386,7 @@ tv_udiff(const struct timeval *start, const struct timeval *end) long udiff; long secdiff = end->tv_sec - start->tv_sec; - if (labs(secdiff+1) > LONG_MAX/1000000) { + if (labs(secdiff)+1 > LONG_MAX/1000000) { log_warn(LD_GENERAL, "comparing times on microsecond detail too far " "apart: %ld seconds", secdiff); return LONG_MAX; @@ -1404,7 +1404,7 @@ tv_mdiff(const struct timeval *start, const struct timeval *end) long mdiff; long secdiff = end->tv_sec - start->tv_sec; - if (labs(secdiff+1) > LONG_MAX/1000) { + if (labs(secdiff)+1 > LONG_MAX/1000) { log_warn(LD_GENERAL, "comparing times on millisecond detail too far " "apart: %ld seconds", secdiff); return LONG_MAX; @@ -1412,7 +1412,13 @@ tv_mdiff(const struct timeval *start, const struct timeval *end) /* Subtract and round */ mdiff = secdiff*1000L + - ((long)end->tv_usec - (long)start->tv_usec + 500L) / 1000L; + /* We add a million usec here to ensure that the result is positive, + * so that the round-towards-zero behavior of the division will give + * the right result for rounding to the nearest msec. Later we subtract + * 1000 in order to get the correct result. + */ + ((long)end->tv_usec - (long)start->tv_usec + 500L + 1000000L) / 1000L + - 1000; return mdiff; } diff --git a/src/test/test_util.c b/src/test/test_util.c index dd600d9..83b48c9 100644 --- a/src/test/test_util.c +++ b/src/test/test_util.c @@ -286,12 +286,12 @@ test_util_time(void *arg) end.tv_usec = 0; tt_int_op(995000L,OP_EQ, tv_udiff(&start, &end)); - // tt_int_op(996L,OP_EQ, tv_mdiff(&start, &end)); // XXXX fails + tt_int_op(995L,OP_EQ, tv_mdiff(&start, &end)); end.tv_sec = 4; tt_int_op(-1005000L,OP_EQ, tv_udiff(&start, &end)); - // tt_int_op(-1005L,OP_EQ, tv_udiff(&start, &end)); // XXXX Fails + tt_int_op(-1005L,OP_EQ, tv_mdiff(&start, &end)); end.tv_sec = TIME_MAX; tt_int_op(LONG_MAX, OP_EQ, tv_udiff(&start, &end));