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utils/UUID_gen: make_nanos_since

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Safely convert millis to "nanos_since" (number of 100
nanseconds since START_EPOCH) while type casting to uint64_t
to avoid possible int overflow.

Signed-off-by: Benny Halevy <bhalevy@scylladb.com>
This commit is contained in:
Benny Halevy
2020-01-27 10:48:47 +02:00
parent 22bac26023
commit cd3460cc88
1 changed files with 7 additions and 3 deletions
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10
utils/UUID_gen.hh
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@@ -77,7 +77,7 @@ private:
// placement of this singleton is important. It needs to be instantiated *AFTER* the other statics.
static thread_local const std::unique_ptr<UUID_gen> instance;
int64_t last_nanos = 0;
uint64_t last_nanos = 0;
UUID_gen()
{
@@ -322,6 +322,10 @@ public:
return (uuid.timestamp() / 10000) + START_EPOCH;
}
static uint64_t make_nanos_since(int64_t millis) {
return (static_cast<uint64_t>(millis) - static_cast<uint64_t>(START_EPOCH)) * 10000;
}
private:
// needs to return two different values for the same when.
@@ -333,7 +337,7 @@ private:
using namespace std::chrono;
int64_t millis = duration_cast<milliseconds>(
system_clock::now().time_since_epoch()).count();
int64_t nanos_since = (millis - START_EPOCH) * 10000;
uint64_t nanos_since = make_nanos_since(millis);
if (nanos_since > last_nanos)
last_nanos = nanos_since;
else
@@ -344,7 +348,7 @@ private:
int64_t create_time_unsafe(int64_t when, int nanos)
{
uint64_t nanos_since = ((when - START_EPOCH) * 10000) + nanos;
uint64_t nanos_since = make_nanos_since(when) + static_cast<uint64_t>(static_cast<int64_t>(nanos));
return create_time(nanos_since);
}