avoid floating point calculations

vvfedorenko · facebook-github-bot · commit 348e9aa2cbf7 · 2025-06-12T15:13:36.000-07:00
Summary: The constant of nanoseconds in second used in the code has type of double while is used in mostly integer operations. Replace it with proper constant. based on https://fb.workplace.com/groups/cpp.is.tricky/permalink/2541032339575142/ Reviewed By: crmdias Differential Revision: D76508594 fbshipit-source-id: 4ac1bc3a96d994391625c7361ad1bb73c5abf5f1
diff --git a/fbclock/cpp_test/test.cpp b/fbclock/cpp_test/test.cpp
@@ -334,17 +334,17 @@ TEST(fbclockTest, test_fbclock_calculate_time_v2) {
       FBCLOCK_TAI);
   ASSERT_EQ(err, 0);
 
-  EXPECT_EQ(truetime.earliest_ns, 1647269091803103381);
-  EXPECT_EQ(truetime.latest_ns, 1647269091803104619);
+  EXPECT_EQ(truetime.earliest_ns, 1647269091803103338);
+  EXPECT_EQ(truetime.latest_ns, 1647269091803104576);
 
   // WOU is very big
   error_bound = 1000.0;
   sysclock_time_ns += 6 * 3600 * 1000000000ULL; // + 6 hours
   err = fbclock_calculate_time_v2(
       error_bound, h_value, &state, sysclock_time_ns, &truetime, FBCLOCK_TAI);
   ASSERT_EQ(err, 0);
-  EXPECT_EQ(truetime.earliest_ns, 1647290691803360857);
-  EXPECT_EQ(truetime.latest_ns, 1647290691803363751);
+  EXPECT_EQ(truetime.earliest_ns, 1647290691803360710);
+  EXPECT_EQ(truetime.latest_ns, 1647290691803363604);
 }
 
 TEST(fbclockTest, test_fbclock_apply_smear_after_2017_leap_second) {
diff --git a/fbclock/fbclock.c b/fbclock/fbclock.c
@@ -37,7 +37,7 @@ limitations under the License.
 #define FBCLOCK_CLOCKDATA_SIZE sizeof(fbclock_clockdata)
 #define FBCLOCK_CLOCKDATA_V2_SIZE sizeof(fbclock_clockdata_v2)
 #define FBCLOCK_MAX_READ_TRIES 1000
-#define NANOSECONDS_IN_SECONDS 1e9
+#define NANOSECONDS_IN_SECONDS 1000000000ULL
 #define SMEAR_DURATION 62500
 
 #ifdef __x86_64__
@@ -470,10 +470,11 @@ uint64_t fbclock_apply_utc_offset(
   int multiplier = state->utc_offset_post_s - state->utc_offset_pre_s;
 
   // Switch to nanoseconds
-  uint64_t smear_end_ns = state->clock_smearing_end_s * 1e9;
-  uint64_t smear_start_ns = state->clock_smearing_start_s * 1e9;
-  uint64_t offset_post_ns = state->utc_offset_post_s * 1e9;
-  uint64_t offset_pre_ns = state->utc_offset_pre_s * 1e9;
+  uint64_t smear_end_ns = state->clock_smearing_end_s * NANOSECONDS_IN_SECONDS;
+  uint64_t smear_start_ns =
+      state->clock_smearing_start_s * NANOSECONDS_IN_SECONDS;
+  uint64_t offset_post_ns = state->utc_offset_post_s * NANOSECONDS_IN_SECONDS;
+  uint64_t offset_pre_ns = state->utc_offset_pre_s * NANOSECONDS_IN_SECONDS;
 
   return fbclock_apply_smear(
       phctime_ns,
@@ -508,10 +509,11 @@ uint64_t fbclock_apply_utc_offset_v2(
 
   // Switch to nanoseconds
   uint64_t smear_end_ns =
-      (state->clock_smearing_start_s + SMEAR_DURATION) * 1e9;
-  uint64_t smear_start_ns = state->clock_smearing_start_s * 1e9;
-  uint64_t offset_post_ns = state->utc_offset_post_s * 1e9;
-  uint64_t offset_pre_ns = state->utc_offset_pre_s * 1e9;
+      (state->clock_smearing_start_s + SMEAR_DURATION) * NANOSECONDS_IN_SECONDS;
+  uint64_t smear_start_ns =
+      state->clock_smearing_start_s * NANOSECONDS_IN_SECONDS;
+  uint64_t offset_post_ns = state->utc_offset_post_s * NANOSECONDS_IN_SECONDS;
+  uint64_t offset_pre_ns = state->utc_offset_pre_s * NANOSECONDS_IN_SECONDS;
 
   return fbclock_apply_smear(
       phctime_ns,
@@ -523,7 +525,7 @@ uint64_t fbclock_apply_utc_offset_v2(
 }
 
 const char* fbclock_strerror(int err_code) {
-  const char* err_info = "unknown error";
+  const char* err_info;
   switch (err_code) {
     case FBCLOCK_E_SHMEM_MAP_FAILED:
       err_info = "shmem map error";
