Problem:
The previous algorithm was not *wrong* but was prone to C type conversion
error.
Previous algorithm:
((A.sec - B.sec) * MSEC_PER_SEC) + ((A.nsec - B.nsec) / NSEC_PER_SEC)
((A.sec - B.sec) * 1000000ULL) + ((A.nsec - B.nsec) / 1000000ULL)
Note that "(A.nsec - B.nsec)" can be negative.
A *quick* fix here is to cast the NSEC_PER_SEC to long allowing a valid
division operation.
The problem was introduced by 395d6b02dda3db1acd08936f49c1dc8efc48e613.
Solution:
Perform the time diff using a temporary timespec struct and perform the
carry operation manually. This prevent negative value for nsec and help
prevent C type promotion problems.
Signed-off-by: Jonathan Rajotte <jonathan.rajotte-jul...@efficios.com>
---
Implement difference without posing the hypothesis that time_a is necessarily
bigger than time_b.
Fixed type in comment.
Added an assert statement to ensure premises before returning. Feel free to
remove.
src/common/sessiond-comm/inet.c | 32 ++++++++++++++++++++++++--------
src/common/sessiond-comm/inet6.c | 32 ++++++++++++++++++++++++--------
2 files changed, 48 insertions(+), 16 deletions(-)
diff --git a/src/common/sessiond-comm/inet.c b/src/common/sessiond-comm/inet.c
index e0b3e7a96..f03fd1fb5 100644
--- a/src/common/sessiond-comm/inet.c
+++ b/src/common/sessiond-comm/inet.c
@@ -119,16 +119,32 @@ static
unsigned long time_diff_ms(struct timespec *time_a,
struct timespec *time_b)
{
- time_t sec_diff;
- long nsec_diff;
- unsigned long result_ms;
+ struct timespec diff;
- sec_diff = time_a->tv_sec - time_b->tv_sec;
- nsec_diff = time_a->tv_nsec - time_b->tv_nsec;
+ if ((time_a->tv_sec > time_b->tv_sec)
+ || ((time_a->tv_sec == time_b->tv_sec)
+ && (time_a->tv_nsec > time_b->tv_nsec))) {
+ /* time_a is bigger */
+ diff.tv_sec = time_a->tv_sec - time_b->tv_sec;
+ diff.tv_nsec = time_a->tv_nsec - time_b->tv_nsec;
+ } else {
+ /* time_b is bigger */
+ diff.tv_sec = time_b->tv_sec - time_a->tv_sec;
+ diff.tv_nsec = time_b->tv_nsec - time_a->tv_nsec;
+ }
- result_ms = sec_diff * MSEC_PER_SEC;
- result_ms += nsec_diff / NSEC_PER_MSEC;
- return result_ms;
+ if (diff.tv_nsec < 0) {
+ /* Perform borrow operation */
+ diff.tv_sec -= 1;
+ diff.tv_nsec += NSEC_PER_SEC;
+ }
+
+ /*
+ * Transform into MSEC, diff.tv_nsec is always positive due to borrow
+ * operation. diff.tv_sec is always positive.
+ */
+ assert(diff.tv_sec >= 0 && diff.tv_nsec >= 0);
+ return (diff.tv_sec * MSEC_PER_SEC) + (diff.tv_nsec / NSEC_PER_MSEC);
}
static
diff --git a/src/common/sessiond-comm/inet6.c b/src/common/sessiond-comm/inet6.c
index dfb5fc5d1..beb2dd9ed 100644
--- a/src/common/sessiond-comm/inet6.c
+++ b/src/common/sessiond-comm/inet6.c
@@ -117,16 +117,32 @@ static
unsigned long time_diff_ms(struct timespec *time_a,
struct timespec *time_b)
{
- time_t sec_diff;
- long nsec_diff;
- unsigned long result_ms;
+ struct timespec diff;
- sec_diff = time_a->tv_sec - time_b->tv_sec;
- nsec_diff = time_a->tv_nsec - time_b->tv_nsec;
+ if ((time_a->tv_sec > time_b->tv_sec)
+ || ((time_a->tv_sec == time_b->tv_sec)
+ && (time_a->tv_nsec > time_b->tv_nsec))) {
+ /* time_a is bigger */
+ diff.tv_sec = time_a->tv_sec - time_b->tv_sec;
+ diff.tv_nsec = time_a->tv_nsec - time_b->tv_nsec;
+ } else {
+ /* time_b is bigger */
+ diff.tv_sec = time_b->tv_sec - time_a->tv_sec;
+ diff.tv_nsec = time_b->tv_nsec - time_a->tv_nsec;
+ }
- result_ms = sec_diff * MSEC_PER_SEC;
- result_ms += nsec_diff / NSEC_PER_MSEC;
- return result_ms;
+ if (diff.tv_nsec < 0) {
+ /* Perform borrow operation */
+ diff.tv_sec -= 1;
+ diff.tv_nsec += NSEC_PER_SEC;
+ }
+
+ /*
+ * Transform into MSEC, diff.tv_nsec is always positive due to borrow
+ * operation. diff.tv_sec is always positive.
+ */
+ assert(diff.tv_sec >= 0 && diff.tv_nsec >= 0);
+ return (diff.tv_sec * MSEC_PER_SEC) + (diff.tv_nsec / NSEC_PER_MSEC);
}
static
--
2.17.1
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