Add analog code model astate.

It reports the previous state (delayed by 1 to 3 time steps)
of the input node. Single or differential voltage or current.

src/xspice/icm/analog/astate/cfunc.mod

@@ -0,0 +1,188 @@
+/*.......1.........2.........3.........4.........5.........6.........7.........8
+================================================================================
+
+FILE astate/cfunc.mod
+
+3-clause BSD
+
+Copyright 2025
+The ngspice team
+
+AUTHORS
+
+    20 September 2025     Holger Vogt
+
+
+MODIFICATIONS
+
+
+
+SUMMARY
+
+    This file contains the functional description of the analog
+    state code model.
+
+
+INTERFACES
+
+    FILE                 ROUTINE CALLED
+
+
+
+REFERENCED FILES
+
+    Inputs from and outputs to ARGS structure.
+
+
+NON-STANDARD FEATURES
+
+    NONE
+
+===============================================================================*/
+
+/*=== INCLUDE FILES ====================*/
+
+#include <stdlib.h>
+
+
+/*=== CONSTANTS ========================*/
+
+
+
+
+/*=== MACROS ===========================*/
+
+
+
+
+/*=== LOCAL VARIABLES & TYPEDEFS =======*/
+
+typedef struct {
+    double    state1;       /* first state value */
+    double    state2;       /* second state value */
+    double    state3;       /* third state value */
+    double    outval;       /* output value */
+    double    xval1;        /* first x value */
+    double    xval2;        /* second x value */
+    double    xval3;        /* third x value */
+} stLocal_Data_t;
+
+
+
+
+
+/*=== FUNCTION PROTOTYPE DEFINITIONS ===*/
+
+static void cm_astate_callback(ARGS, Mif_Callback_Reason_t reason);
+
+/*=== CM_STATE ROUTINE ===*/
+
+void cm_astate(ARGS)
+{
+    int state_number = 0;
+    double outval = 0.0;
+
+    stLocal_Data_t *loc;        /* Pointer to local static data, not to be included
+                                       in the state vector */
+
+
+    if (ANALYSIS != MIF_AC) {     /**** only Transient Analysis and dc ****/
+
+        /** INIT: allocate storage **/
+
+        if (INIT==1) {
+
+            CALLBACK = cm_astate_callback;
+
+            /*** allocate static storage for *loc ***/
+            if ((loc = (stLocal_Data_t *) (STATIC_VAR(locdata) = calloc(1,
+                    sizeof(stLocal_Data_t)))) == (stLocal_Data_t *) NULL) {
+                cm_message_send("Unable to allocate Local_Data_t "
+                    "in cm_astate()");
+                return;
+            }
+            loc->state1 = 0;
+            loc->state2 = 0;
+            loc->state3 = 0;
+            loc->outval = 0;
+            loc->xval1 = 0;
+            loc->xval2 = 0;
+            loc->xval3 = 0;
+        }
+
+        /* retrieve previous values */
+
+        loc = STATIC_VAR (locdata);
+
+        state_number = PARAM(astate_no);
+
+        if (state_number == 0) {
+            OUTPUT(out) = INPUT(in);
+            return;
+        }
+
+        if (TIME == loc->xval1) {
+            switch(state_number) {
+                case 1:
+                    loc->outval = loc->state1;
+                    break;
+                case 2:
+                    loc->outval = loc->state2;
+                    break;
+                case 3:
+                    loc->outval = loc->state3;
+                    break;
+                default: 
+                    loc->outval = INPUT(in);
+                    break;
+            }
+        }
+        else if (TIME > loc->xval1) {
+            loc->state3 = loc->state2;
+            loc->state2 = loc->state1;
+            loc->state1 = INPUT(in);
+
+            loc->xval3 = loc->xval2;
+            loc->xval2 = loc->xval1;
+            loc->xval1 = TIME;
+        }
+        /* initial time iteration */
+        else if (TIME == 0.0) {
+            loc->state1 = loc->outval = INPUT(in);
+            loc->xval1 = 0.0;
+        }
+        /* time step rejected ? */
+        else if (TIME < loc->xval1){
+            loc->state1 = INPUT(in);
+            loc->xval1 = TIME;
+        }
+        /* output */
+        if (ANALYSIS == MIF_TRAN) {
+            OUTPUT(out) = loc->outval;
+        }
+        else { /* dc */
+            OUTPUT(out) = INPUT(in);
+        }
+    }
+    else {
+        OUTPUT(out) = INPUT(in);
+    }
+}
+
+/* free the memory created locally */
+static void cm_astate_callback(ARGS, Mif_Callback_Reason_t reason)
+{
+    switch (reason) {
+        case MIF_CB_DESTROY: {
+            stLocal_Data_t *loc = (stLocal_Data_t *) STATIC_VAR(locdata);
+            if (loc == (stLocal_Data_t *) NULL) {
+                break;
+            }
+
+            free(loc);
+
+            STATIC_VAR(locdata) = NULL;
+            break;
+        }
+    }
+} /* end of function cm_astate_callback */

src/xspice/icm/analog/astate/ifspec.ifs

@@ -0,0 +1,58 @@
+/*.......1.........2.........3.........4.........5.........6.........7.........8
+================================================================================
+
+-------------------------------------------------------------------------
+ Copyright 2025
+ The ngspice team
+ 3 - Clause BSD license
+ (see COPYING or https://opensource.org/licenses/BSD-3-Clause)
+-------------------------------------------------------------------------
+
+AUTHORS
+
+    20 September 2025     Holger Vogt
+
+
+SUMMARY
+
+    This file contains the interface specification file for the
+    astate code model.
+
+===============================================================================*/
+
+NAME_TABLE:
+
+C_Function_Name:       cm_astate
+Spice_Model_Name:      astate
+Description:           "analog state return"
+
+
+PORT_TABLE:
+
+Port_Name:             in                  out
+Description:           "input"             "output"
+Direction:             in                  out
+Default_Type:          v                   v
+Allowed_Types:         [v,vd,vnam,i,id]    [v,vd,i,id]
+Vector:                no                  no
+Vector_Bounds:          -                  -
+Null_Allowed:          no                  no
+
+
+PARAMETER_TABLE:
+
+Parameter_Name:     astate_no
+Description:        "state to be returned"
+Data_Type:          int
+Default_Value:      1
+Limits:             [0 3]
+Vector:             no
+Vector_Bounds:       -
+Null_Allowed:       yes
+
+
+STATIC_VAR_TABLE:
+
+Static_Var_Name:    locdata
+Description:        "local static data"
+Data_Type:          pointer

src/xspice/icm/analog/modpath.lst

@@ -20,3 +20,4 @@ triangle
 file_source
 delay
 pwlts
+astate