13c496b79b

util/include/rusefi/rusefi_time_wraparound.h

@@ -0,0 +1,29 @@
+/**
+ * Provide a 62-bit counter from a 32-bit counter source that wraps around.
+ *
+ * If you'd like it use it with a 16-bit counter, shift the source by 16 before passing it here.
+ * This class is thread/interrupt-safe.
+ */
+struct WrapAround62 {
+	uint64_t update(uint32_t source) {
+		// Shift cannot be 31, as we wouldn't be able to tell if time is moving forward or
+		// backward relative to m_upper.  We do need to handle both directions as our
+		// "thread" can be racing with other "threads" in sampling stamp and updating
+		// m_upper.
+		constexpr unsigned shift = 30;
+
+		uint32_t upper = m_upper;
+		uint32_t relative_unsigned = source - (upper << shift);
+		upper += int32_t(relative_unsigned) >> shift;
+		m_upper = upper;
+
+		// Yes we could just do upper<<shift, but then the result would span both halves of
+		// the 64-bit result.  Doing it this way means we only operate on one half at a
+		// time.  Source will supply those bits anyways, so we don't need them from
+		// upper...
+		return (efitick_t(upper >> (32 - shift)) << 32) | source;
+	}
+
+private:
+	volatile uint32_t m_upper = 0;
+};