Avoid unnecessary checking in getting current time on 32-bit systems.

base/time/time_posix.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "base/time/time.h"
 
 #include <stdint.h>
 #include <sys/time.h>
 #include <time.h>
 #if defined(OS_ANDROID) && !defined(__LP64__)
@@ skipping 62 matching lines @@
 void SysTimeToTimeStruct(SysTime t, struct tm* timestruct, bool is_local) {
   base::AutoLock locked(g_sys_time_to_time_struct_lock.Get());
   if (is_local)
     localtime_r(&t, timestruct);
   else
     gmtime_r(&t, timestruct);
 }
 #endif  // OS_ANDROID
 
 int64_t ConvertTimespecToMicros(const struct timespec& ts) {
-  base::CheckedNumeric<int64_t> result(ts.tv_sec);
-  result *= base::Time::kMicrosecondsPerSecond;
-  result += (ts.tv_nsec / base::Time::kNanosecondsPerMicrosecond);
-  return result.ValueOrDie();
+  // On 32-bit systems, the calculation cannot overflow int64_t.
+  // 2**32 * 1000000 + 2**64 / 1000 < 2**63
+  if (sizeof(ts.tv_sec) <= 4 && sizeof(ts.tv_nsec) <= 8) {
+    int64_t result = ts.tv_sec;
+    result *= base::Time::kMicrosecondsPerSecond;
+    result += (ts.tv_nsec / base::Time::kNanosecondsPerMicrosecond);
+    return result;
+  } else {
+    base::CheckedNumeric<int64_t> result(ts.tv_sec);
+    result *= base::Time::kMicrosecondsPerSecond;
+    result += (ts.tv_nsec / base::Time::kNanosecondsPerMicrosecond);
+    return result.ValueOrDie();
+  }
 }
 
 // Helper function to get results from clock_gettime() and convert to a
 // microsecond timebase. Minimum requirement is MONOTONIC_CLOCK to be supported
 // on the system. FreeBSD 6 has CLOCK_MONOTONIC but defines
 // _POSIX_MONOTONIC_CLOCK to -1.
 #if (defined(OS_POSIX) &&                                               \
      defined(_POSIX_MONOTONIC_CLOCK) && _POSIX_MONOTONIC_CLOCK >= 0) || \
     defined(OS_BSD) || defined(OS_ANDROID)
 int64_t ClockNow(clockid_t clk_id) {
@@ skipping 285 matching lines @@
     result.tv_usec = static_cast<suseconds_t>(Time::kMicrosecondsPerSecond) - 1;
     return result;
   }
   int64_t us = us_ - kTimeTToMicrosecondsOffset;
   result.tv_sec = us / Time::kMicrosecondsPerSecond;
   result.tv_usec = us % Time::kMicrosecondsPerSecond;
   return result;
 }
 
 }  // namespace base