Add Crystal::System::Time.ticks

Returns the current time as per the monotonic clock in nanoseconds.
Doesn't fail (i.e. doesn't raise) and doesn't allocate into the GC
HEAP, so we can use it in tight contexts.

src/crystal/system/time.cr

@@ -7,6 +7,10 @@ module Crystal::System::Time
   # nanoseconds}`.
   # def self.monotonic : {Int64, Int32}
 
+  # Returns the current time from the monotonic clock in nanoseconds.
+  # Doesn't raise nor allocates GC HEAP memory.
+  # def self.ticks : UInt64
+
   # Returns a list of paths where time zone data should be looked up.
   # def self.zone_sources : Enumerable(String)
 

src/crystal/system/unix/time.cr

@@ -46,6 +46,16 @@ module Crystal::System::Time
     {% end %}
   end
 
+  def self.ticks : UInt64
+    {% if flag?(:darwin) %}
+      info = mach_timebase_info
+      LibC.mach_absolute_time &* info.numer // info.denom
+    {% else %}
+      LibC.clock_gettime(LibC::CLOCK_MONOTONIC, out tp)
+      tp.tv_sec.to_u64! &* NANOSECONDS_PER_SECOND &+ tp.tv_nsec.to_u64!
+    {% end %}
+  end
+
   def self.to_timespec(time : ::Time)
     t = uninitialized LibC::Timespec
     t.tv_sec = typeof(t.tv_sec).new(time.to_unix)

src/crystal/system/win32/time.cr

@@ -66,7 +66,11 @@ module Crystal::System::Time
     LibC.QueryPerformanceCounter(out ticks)
     frequency = performance_frequency
     {ticks // frequency, (ticks.remainder(frequency) * NANOSECONDS_PER_SECOND / frequency).to_i32}
+  end
 
+  def self.ticks : UInt64
+    LibC.QueryPerformanceCounter(out ticks)
+    ticks.to_u64! &* (NANOSECONDS_PER_SECOND // performance_frequency)
   end
 
   def self.load_localtime : ::Time::Location?