add comment in the code

src/xspice/mif/mifsetup.c

@@ -17,6 +17,7 @@ AUTHORS
 MODIFICATIONS
 
     <date> <person name> <nature of modifications>
+    1 oct. 2020 Florian Ballenegger  Added support for instance parameters
 
 SUMMARY
 
@@ -84,6 +85,43 @@ entries in the SPICE matrix and the storage of pointers to
 locations of the matrix used by MIFload during a simulation.
 */
 
+/*
+Support for instance parameters: how it works
+
+cmpp is modified to recognize the new 'parameter_scope' keyword
+in ifspec.ifs files, which can be set to 'model', 'instance', or 'both'.
+
+All parameters are filled in the xspice parameter descriptor, as before.
+
+Instance parameters spice descriptors are added when ifspec.ifs
+is translated (xspice/cmpp/writ_ifs.c).
+Use the index in the xspice list of parameter descriptors as key id.
+Instance parameters are put first, followed by instance static variables.
+Parameters which have instance scope only are filtered out the model
+parameter spice descriptors.
+
+A new field 'iparam' is added in the Mif_Private_t struct to point to the
+table of instance parameters values, which is stored in the MIFinstance
+and allocated in mif_inp2.c.
+
+Model object MIFmodel still hold entries for all parameters in 'param',
+including instance parameters. The wasted memory is considered small as
+there is usually less models than instances.
+
+In the codemodel code generated by cmpp from cfunc.mod, the access to
+parameters that have instance scope is modified to point to the iparam
+entry of Mif_Private_t (xspice/cmpp/mod_yacc.y). Relevant index to
+iparam table is calculated by cmpp.
+
+A new MIFParam function is added to the core interface.
+MIFask and MIFmParam are modified.
+
+Parsing for A devices is modified at several places
+(mif_inp2.c, subckt.c, inpcom.c)
+
+Florian Ballenegger (Anamosic), October 2020.
+*/
+
 
 int
 MIFsetup(