[wperf, wperf-test] WPERF-965: Refactor to turn repeated code into a seperate function

See merge request Linaro/WindowsPerf/windowsperf!684

=== ChangeLog ===

* code tidy for timestamps_to_duration function

* refactor to make calculation of 'duration' from 'timestamps' into a seperate function/file

Author: kush-kothari-arm

wperf/main.cpp

@@ -390,17 +390,7 @@ wmain(
                     pmu_device.print_dmc_stat(request.ioctl_events[EVT_DMC_CLK], request.ioctl_events[EVT_DMC_CLKDIV2], request.report_ddr_bw_metric);
                 }
 
-                ULARGE_INTEGER li_a, li_b;
-                FILETIME time_a, time_b;
-
-                SystemTimeToFileTime(&timestamp_a, &time_a);
-                SystemTimeToFileTime(&timestamp_b, &time_b);
-                li_a.u.LowPart = time_a.dwLowDateTime;
-                li_a.u.HighPart = time_a.dwHighDateTime;
-                li_b.u.LowPart = time_b.dwLowDateTime;
-                li_b.u.HighPart = time_b.dwHighDateTime;
-
-                const double duration = (double)(li_b.QuadPart - li_a.QuadPart) / 10000000.0;
+                const double  duration = timestamps_to_duration(timestamp_a, timestamp_b);
                 m_globalJSON.m_duration = duration;
 
                 if (!request.do_timeline)
@@ -1290,17 +1280,7 @@ wmain(
                     << std::wstring(PrettyTable<wchar_t>::m_COLUMN_SEPARATOR, L' ') <<  L"top " << std::dec << printed_sample_num << L" in total" << std::endl;
             }
 
-            ULARGE_INTEGER li_a, li_b;
-            FILETIME time_a, time_b;
-
-            SystemTimeToFileTime(&timestamp_a, &time_a);
-            SystemTimeToFileTime(&timestamp_b, &time_b);
-            li_a.u.LowPart = time_a.dwLowDateTime;
-            li_a.u.HighPart = time_a.dwHighDateTime;
-            li_b.u.LowPart = time_b.dwLowDateTime;
-            li_b.u.HighPart = time_b.dwHighDateTime;
-
-            const double duration = (double)(li_b.QuadPart - li_a.QuadPart) / 10000000.0;
+            const double  duration = timestamps_to_duration(timestamp_a, timestamp_b);
             m_globalJSON.m_duration = duration;
 
             if (!request.do_timeline)

wperf/wperf.cpp

@@ -122,3 +122,21 @@ GetDevicePath(
 
     return bRet;
 }
+
+double timestamps_to_duration(const SYSTEMTIME& timestamp_a, const SYSTEMTIME& timestamp_b) 
+{
+    ULARGE_INTEGER li_a, li_b;
+    FILETIME time_a, time_b;
+
+    SystemTimeToFileTime(&timestamp_a, &time_a);
+    SystemTimeToFileTime(&timestamp_b, &time_b);
+
+    li_a.u.LowPart = time_a.dwLowDateTime;
+    li_a.u.HighPart = time_a.dwHighDateTime;
+    li_b.u.LowPart = time_b.dwLowDateTime;
+    li_b.u.HighPart = time_b.dwHighDateTime;
+
+    double duration = (double)(li_b.QuadPart - li_a.QuadPart) / 10000000.0;
+
+    return duration;
+}

wperf/wperf.h

@@ -38,3 +38,5 @@ GetDevicePath(
     _Out_writes_(BufLen) PWCHAR DevicePath,
     _In_ size_t BufLen
 );
+
+double timestamps_to_duration(const SYSTEMTIME& timestamp_a, const SYSTEMTIME& timestamp_b);