add hal_extend_int function

helper function to deal with wrap around and extension of lower-width counters to 64bit ints.

Author: Robert Schöftner

src/hal/hal.h

@@ -692,6 +692,24 @@ extern int hal_get_signal_value_by_name(
 extern int hal_get_param_value_by_name(
     const char *name, hal_type_t *type, hal_data_u **data);
 
+/***********************************************************************
+*                    MISC HELPER FUNCTIONS                             *
+************************************************************************/
+
+/** hal_extend_counter() extends a counter value with nbits to 64 bits.
+    
+    For some hardware counters it may be desireable to extend their
+    range beyond their native width.
+
+    This function maintains a 64bit counter value and deals with wrap
+    arounds. Increments between updates need to be less than 2**(nbits-1).
+    Call with current 64bit counter value to be updated as @param old,
+    new lower-bit counter value read from hardware as @param newlow 
+    and width of counter as @param nbits.
+    @returns new counter 64bit counter value.
+    Code by Jeff Epler. */
+extern rtapi_s64 hal_extend_int(rtapi_s64 old, rtapi_s64 newlow, int nbits);
+
 /***********************************************************************
 *                   EXECUTION RELATED FUNCTIONS                        *
 ************************************************************************/