Add timeradd and timersub to the sys/time.h portability header

Summary: I missed these in my initial diff.

Reviewed By: yfeldblum

Differential Revision: D2989977

fb-gh-sync-id: 0efb92286a8aed91ec1d394572cd709e5b6b37ab
shipit-source-id: 0efb92286a8aed91ec1d394572cd709e5b6b37ab

folly/portability/SysTime.cpp

@@ -20,7 +20,8 @@
 #include <cstdint>
 #include <Windows.h>
 
-extern "C" int gettimeofday(timeval* tv, timezone*) {
+extern "C" {
+int gettimeofday(timeval* tv, timezone*) {
   constexpr auto posixWinFtOffset = 116444736000000000ULL;
 
   if (tv) {
@@ -33,4 +34,23 @@ extern "C" int gettimeofday(timeval* tv, timezone*) {
 
   return 0;
 }
+
+void timeradd(timeval* a, timeval* b, timeval* res) {
+  res->tv_sec = a->tv_sec + b->tv_sec;
+  res->tv_usec = a->tv_usec + b->tv_usec;
+  if (res->tv_usec >= 1000000) {
+    res->tv_sec++;
+    res->tv_usec -= 1000000;
+  }
+}
+
+void timersub(timeval* a, timeval* b, timeval* res) {
+  res->tv_sec = a->tv_sec - b->tv_sec;
+  res->tv_usec = a->tv_usec - b->tv_usec;
+  if (res->tv_usec < 0) {
+    res->tv_sec--;
+    res->tv_usec += 1000000;
+  }
+}
+}
 #endif

folly/portability/SysTime.h

@@ -26,5 +26,9 @@ struct timezone {
   int tz_dsttime;
 };
 
-extern "C" int gettimeofday(timeval* tv, timezone*);
+extern "C" {
+int gettimeofday(timeval* tv, timezone*);
+void timeradd(timeval* a, timeval* b, timeval* res);
+void timersub(timeval* a, timeval* b, timeval* res);
+}
 #endif