Add localtime

This makes a call to GetTimeZoneInformation in winapi/timezoneapi.h, offsets the time given by the output of GetTimeZoneInformation, passes it to gmtime, and returns the result from gmtime.

Author: PQCraft

functions/time/localtime.c

@@ -0,0 +1,49 @@
+/* localtime( const time_t * )
+
+   This file is part of the Public Domain C Library (PDCLib).
+   Permission is granted to use, modify, and / or redistribute at will.
+*/
+
+#include <time.h>
+#include <timezoneapi.h>
+
+#ifndef REGTEST
+
+struct tm * localtime( const time_t * timer )
+{
+    TIME_ZONE_INFORMATION tzinfo;
+    DWORD tz = GetTimeZoneInformation( &tzinfo );
+
+    if ( tz == TIME_ZONE_ID_INVALID )
+    {
+        return NULL;
+    }
+    if ( tz == TIME_ZONE_ID_STANDARD )
+    {
+        tzinfo.Bias += tzinfo.StandardBias;
+    }
+    else if ( tz == TIME_ZONE_ID_DAYLIGHT )
+    {
+        tzinfo.Bias += tzinfo.DaylightBias;
+    }
+
+    time_t ltimer = *timer - tzinfo.Bias * 60;
+
+    struct tm * ret = gmtime( &ltimer );
+
+    return ret;
+}
+
+#endif
+
+#ifdef TEST
+
+#include "_PDCLIB_test.h"
+
+int main( void )
+{
+    TESTCASE( NO_TESTDRIVER );
+    return TEST_RESULTS;
+}
+
+#endif