util: Some corrections for timespec_diff_us

The comment for timespec_diff_us() claims it will wrap after 2^64µs.  This
is incorrect for two reasons:
  * It returns a long long, which is probably 64-bits, but might not be
  * It returns a signed value, so even if it is 64 bits it will wrap after
    2^63µs

Correct the comment and use an explicitly 64-bit type to avoid that
imprecision.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>

2 files changed, 3 insertions, 3 deletions

diff --git a/util.c b/util.c
index 54a9f58..07fb21c 100644
--- a/util.c
+++ b/util.c
@@ -244,9 +244,9 @@ void sock_probe_mem(struct ctx *c)
  * @a:		Minuend timestamp
  * @b:		Subtrahend timestamp
  *
- * Return: difference in microseconds (wraps after 2^64 / 10^6s ~= 585k years)
+ * Return: difference in microseconds (wraps after 2^63 / 10^6s ~= 292k years)
  */
-long long timespec_diff_us(const struct timespec *a, const struct timespec *b)
+int64_t timespec_diff_us(const struct timespec *a, const struct timespec *b)
 {
 	if (a->tv_nsec < b->tv_nsec) {
 		return (b->tv_nsec - a->tv_nsec) / 1000 +
diff --git a/util.h b/util.h
index e8bf957..83d2b53 100644
--- a/util.h
+++ b/util.h
@@ -168,7 +168,7 @@ int sock_l4(const struct ctx *c, sa_family_t af, enum epoll_type type,
 	    uint32_t data);
 void sock_probe_mem(struct ctx *c);
 long timespec_diff_ms(const struct timespec *a, const struct timespec *b);
-long long timespec_diff_us(const struct timespec *a, const struct timespec *b);
+int64_t timespec_diff_us(const struct timespec *a, const struct timespec *b);
 void bitmap_set(uint8_t *map, unsigned bit);
 void bitmap_clear(uint8_t *map, unsigned bit);
 bool bitmap_isset(const uint8_t *map, unsigned bit);