Try to clarify the mechanism of parameter substitution and add

an example of substituting an XSPICE vector parameter.

examples/numparam/vector_param.cir

@@ -0,0 +1,33 @@
+.TITLE SUBCKT VECTOR PARAM TEST
+* Example of passing a vector parameter to a sub-circuit.
+* Modified from https://sourceforge.net/p/ngspice/feature-requests/55/
+
+* An AND gate impmented as a LUT in a subcircuit.
+
+.param default_vec="[1e-12 2e-12]"
+                                    *--vector parameter--
+.subckt testcir in0 in1 outlut testpar = {default_vec}
+
+A_genlut [in0 in1] [outlut] genlut
+.model genlut d_genlut (
++ input_delay  = {testpar}
++ table_values = "0001")
+
+.ends testcir
+
+V_Vss vss 0 DC 3.3
+V_pulse sine 0 DC 0 SIN(0 1 1000)
+
+.param actual_vec="[1.3e-3 2e-3]"
+                                    *--vector parameter--
+X_subckt no1 dss node3 testcir testpar={actual_vec}
+
+A_ADC [sine vss] [no1 dss] ADC
+.model ADC adc_bridge(in_low=0.7 in_high=0.71)
+
+.control
+  tran 20u 4m
+  plot sine node3
+.endc
+
+.end

src/frontend/numparam/numparam.h

@@ -20,6 +20,11 @@ extern const struct nupa_type S_nupa_string;
 extern const struct nupa_type S_nupa_subckt;
 extern const struct nupa_type S_nupa_unknown;
 
+/* Length of "numparam____ ..." string to be inserted and replaced. */
+
+#define ACT_CHARACTS 25
+#define MARKER "numparm__________"
+
 #define  NUPA_REAL     (&S_nupa_real)
 #define  NUPA_STRING   (&S_nupa_string)
 #define  NUPA_SUBCKT   (&S_nupa_subckt)

src/frontend/numparam/spicenum.c

@@ -121,8 +121,9 @@ stripbraces(DSTRINGPTR dstr_p)
 
         cadd(&tstr, ' ');
         {
-            char buf[25+1];
-            sprintf(buf, "numparm__________%08lx", ++placeholder);
+            char buf[ACT_CHARACTS + 1];
+
+            sprintf(buf, MARKER "%08lx", ++placeholder);
             sadd(&tstr, buf);
         }
         cadd(&tstr, ' ');

src/frontend/numparam/xpressn.c

@@ -23,8 +23,6 @@
 
 extern long dynsubst;           /* see inpcom.c */
 
-#define ACT_CHARACTS 25      /* actual string length to be inserted and replaced */
-
 #define  S_init   0
 #define  S_atom   1
 #define  S_binop  2
@@ -1165,7 +1163,7 @@ static char *string_expr(dico_t *dico, DSTRINGPTR qstr_p,
 
 /* stupid, produce a string representation of a given double
  *   to be spliced back into the circuit deck
- * we want *exactly* 25 chars, we have
+ * we want *exactly* 25 (ACT_CHARACTS) chars, we have
  *   sign, leading digit, '.', 'e', sign, upto 3 digits exponent
  * ==> 8 chars, thus we have 17 left for precision
  * don't print a leading '+', something choked
@@ -1214,10 +1212,10 @@ insertnumber(dico_t *dico, char **lp, DSTRINGPTR ustr_p)
     long        id = 0;
     int         n;
 
-    char *p = strstr(s, "numparm__________");
+    char *p = strstr(s, MARKER);
 
     if (p &&
-        (1 == sscanf(p, "numparm__________%8lx%n", &id, &n)) &&
+        (1 == sscanf(p, MARKER "%8lx%n", &id, &n)) &&
         (n == ACT_CHARACTS) &&
         (id > 0) && (id < dynsubst + 1)) {
         /* Found a target for substitution. */