From 576f2189452fca4fb15495bccc8acb925fb6973c Mon Sep 17 00:00:00 2001
From: Giles Atkinson <“gatk555@gmail.com”>
Date: Thu, 22 Jun 2023 16:47:27 +0100
Subject: [PATCH] Fix the NAND and NOR variants of XSPICE code model
 multi_input_pwl and add an example of its use with the E-source NAND variant.

---
 examples/digital/compare/adder-comparison.txt |  8 +-
 examples/digital/compare/adder_esource.cir    | 16 ++++
 .../icm/analog/multi_input_pwl/cfunc.mod      | 78 +++++++++++++++----
 .../icm/analog/multi_input_pwl/ifspec.ifs     |  8 ++
 4 files changed, 94 insertions(+), 16 deletions(-)
 create mode 100644 examples/digital/compare/adder_esource.cir

diff --git a/examples/digital/compare/adder-comparison.txt b/examples/digital/compare/adder-comparison.txt
index ef3e28e12..56972e94e 100644
--- a/examples/digital/compare/adder-comparison.txt
+++ b/examples/digital/compare/adder-comparison.txt
@@ -1,4 +1,4 @@
-Compare four different 4-bit full adders,
+Compare five different 4-bit full adders,
 made of NAND gates
 Simulating for 6400ns
 
@@ -21,3 +21,9 @@ Fully digital, event node based NAND gates
 digital plotting into vcd file, display with gtkwave
 Simulation time 0.27s
 
+adder_esource
+Uses the NAND variant of the E-type behavioral voltage source.
+
+There are further variations of adder_Xspice in directory
+examples/digital/auto_bridge.
+
diff --git a/examples/digital/compare/adder_esource.cir b/examples/digital/compare/adder_esource.cir
new file mode 100644
index 000000000..62ee85673
--- /dev/null
+++ b/examples/digital/compare/adder_esource.cir
@@ -0,0 +1,16 @@
+  ADDER - 4 BIT BINARY ADDER USING E-SOURCE AND GATES
+  * behavioral gate description
+
+*** SUBCIRCUIT DEFINITION
+
+.SUBCKT 74HC00  in1 in2 out  NVCC NVGND  vcc1={vcc} tripdt1={tripdt}
+.param Rout={60*4.0/(vcc1-0.5)} ; standard output driver
+E1 out20 0 nand(2) in1 0 in2 0 ({vcc / 3}, 0) ({2 * vcc / 3}, {vcc})
+Rout out20 out {Rout}
+.ends
+
+.param vcc=3 tripdt=6n
+
+.include ../adder_common.inc
+
+.END
diff --git a/src/xspice/icm/analog/multi_input_pwl/cfunc.mod b/src/xspice/icm/analog/multi_input_pwl/cfunc.mod
index 5758ce546..91e228c2e 100644
--- a/src/xspice/icm/analog/multi_input_pwl/cfunc.mod
+++ b/src/xspice/icm/analog/multi_input_pwl/cfunc.mod
@@ -174,33 +174,81 @@ get_output( ARGS, double x )
   return result;
 }
 
+static double
+get_reverse_output( ARGS, double x )
+{
+  int    size   = PARAM_SIZE(x);
+  double result = 0;
+  double slope  = 0;
+  int    i;
+
+  /* check if x beyond specified limits */
+  if ( x <= PARAM(x[0])      ) return PARAM(y[size-1]);
+  if ( x >= PARAM(x[size-1]) ) return PARAM(y[0]);
+
+  for ( i = 1; i < size; i++ )
+    if ( x > PARAM(x[i-1]) && x <= PARAM(x[i]) )
+      {
+        result = PARAM(y[size - i - 1]) + slope * (x - PARAM(x[i - 1]));
+	break;
+      }
+  return result;
+}
+
 void
 cm_multi_input_pwl(ARGS) 
 {
-  const char*  model = ( PARAM_NULL(model) == 1 ) ? "and" : PARAM(model);
+  const char*  model = PARAM(model);
   double output;
 
-  if ( ANALYSIS == TRANSIENT || ANALYSIS == DC )
-    {
-      if ( strcmp( model, "and"  ) != 0 && strcmp( model, "or"  ) != 0 &&
-	   strcmp( model, "nand" ) != 0 && strcmp( model, "nor" ) != 0 )
-	{
-	  fprintf( stderr, "ERROR(cm_multi_input_pwl): unknown gate model type '%s'; expecting 'and|or|nand|nor'.\n", model );
+  if (INIT) {
+      int type;
+
+      if (!strcmp(model, "and"))
+          type = 0;
+      else if (!strcmp(model, "nand"))
+          type = 1;
+      else if (!strcmp(model, "or"))
+          type = 2;
+      else if (!strcmp(model, "nor"))
+          type = 3;
+      else {
+	  fprintf(stderr, "ERROR(cm_multi_input_pwl): unknown gate model type "
+                  "'%s'; expecting 'and|or|nand|nor'.\n", model );
 	  exit(-1);
-	}
-      if ( PARAM_SIZE(x) != PARAM_SIZE(y) )
-	{
-	  fprintf( stderr, "ERROR(cm_multi_input_pwl): 'x' and 'y' input vectors are not the same size!\n" );
-	  exit(-1);
-	}
+      }
+      STATIC_VAR(type) = type;
+      if ( PARAM_SIZE(x) != PARAM_SIZE(y) ) {
+	  fprintf(stderr, "ERROR(cm_multi_input_pwl): 'x' and 'y' input vectors are not the same size!\n" );
+	  if (PARAM_SIZE(x) > PARAM_SIZE(y))
+              PARAM_SIZE(x) = PARAM_SIZE(y);
+      }
+  }
+
+  if ( ANALYSIS == TRANSIENT || ANALYSIS == DC ) {
       /*
 	Iterate through each input and find output value
 	  and/nand: controlling input is chosen on the basis of the smallest value
 	  or/nor:   controlling input is chosen on the basis of the largest value
       */
-      if (strstr(model, "and")) output = get_output(mif_private, get_smallest_input(mif_private));
-      else                      output = get_output(mif_private, get_largest_input(mif_private));
 
+      switch (STATIC_VAR(type)) {
+      case 0:
+      default:
+          output = get_output(mif_private, get_smallest_input(mif_private));
+          break;
+      case 1:
+          output = get_reverse_output(mif_private,
+                                      get_smallest_input(mif_private));
+          break;
+      case 2:
+          output = get_output(mif_private, get_largest_input(mif_private));
+          break;
+      case 3:
+          output = get_reverse_output(mif_private,
+                                      get_largest_input(mif_private));
+          break;
+      }
       OUTPUT(out) = output;
     }
 }
diff --git a/src/xspice/icm/analog/multi_input_pwl/ifspec.ifs b/src/xspice/icm/analog/multi_input_pwl/ifspec.ifs
index c87b0e471..852c2bda9 100644
--- a/src/xspice/icm/analog/multi_input_pwl/ifspec.ifs
+++ b/src/xspice/icm/analog/multi_input_pwl/ifspec.ifs
@@ -49,3 +49,11 @@ Limits:                -                  -               -
 Vector:                yes                yes             no
 Vector_Bounds:         [2 -]              [2 -]           -
 Null_Allowed:          no                 no              yes
+
+/* This is used internally to cache the model type. */
+
+STATIC_VAR_TABLE:
+
+Static_Var_Name:    type
+Description:        "Internal copy of model type"
+Data_Type:          int