api change for ngdirname() to fix a memory leak

ngdirname did `own' the returned string.
now the invoker is responsible for the returned string.

note, this is contrary to the POSIX dirname() implementation,
   which *might* return pointers to statical allocated memory.

src/frontend/device.c

@@ -1455,7 +1455,11 @@ static void com_alter_mod(wordlist *wl)
         filename = copy(eqword);
     }
     modfile = inp_pathopen(filename, readmode);
-    inp_readall(modfile, &modeldeck, 0, ngdirname(filename), 0);
+    {
+        char *dir_name = ngdirname(filename);
+        inp_readall(modfile, &modeldeck, 0, dir_name, 0);
+        free(dir_name);
+    }
     tfree(input);
     tfree(filename);
     /* get all lines starting with *model */

src/frontend/inp.c

@@ -293,12 +293,12 @@ inp_spsource(FILE *fp, bool comfile, char *filename)
     double startTime, endTime;
 
     /* read in the deck from a file */
-    char *filename_dup = (filename == NULL) ? strdup(".") : strdup(filename);
+    char *dir_name = ngdirname(filename ? filename : ".");
 
     startTime = seconds();
-    inp_readall(fp, &deck, 0, ngdirname(filename_dup), comfile);
+    inp_readall(fp, &deck, 0, dir_name, comfile);
     endTime = seconds();
-    tfree(filename_dup);
+    tfree(dir_name);
 
     /* if nothing came back from inp_readall, just close fp and return to caller */
     if (!deck) {        /* MW. We must close fp always when returning */

src/frontend/inpcom.c

@@ -310,9 +310,9 @@ inp_readall(FILE *fp, struct line **data, int call_depth, char *dir_name, bool c
                     library_file[num_libraries++] = strdup(y);
 
                     if ( dir_name_flag == FALSE ) {
-                        char *s_dup = strdup(y);
-                        inp_readall(newfp, &libraries[num_libraries-1], call_depth+1, ngdirname(s_dup), FALSE);
-                        tfree(s_dup);
+                        char *y_dir_name = ngdirname(y);
+                        inp_readall(newfp, &libraries[num_libraries-1], call_depth+1, y_dir_name, FALSE);
+                        tfree(y_dir_name);
                     } else {
                         inp_readall(newfp, &libraries[num_libraries-1], call_depth+1, dir_name, FALSE);
                     }
@@ -387,9 +387,9 @@ inp_readall(FILE *fp, struct line **data, int call_depth, char *dir_name, bool c
                 }
 
                 if ( dir_name_flag == FALSE ) {
-                    char *s_dup = strdup(y);
-                    inp_readall(newfp, &newcard, call_depth+1, ngdirname(s_dup), FALSE);  /* read stuff in include file into netlist */
-                    tfree(s_dup);
+                    char *y_dir_name = ngdirname(y);
+                    inp_readall(newfp, &newcard, call_depth+1, y_dir_name, FALSE);  /* read stuff in include file into netlist */
+                    tfree(y_dir_name);
                 } else {
                     inp_readall(newfp, &newcard, call_depth+1, dir_name, FALSE);  /* read stuff in include file into netlist */
                 }

src/misc/ivars.c

@@ -88,6 +88,7 @@ ivars(char *argv0)
         /* set path either to <ngspice-bin-directory>/input or,
         if set, to environment variable NGSPICE_INPUT_DIR */
         mkvar(&Inp_Path, ngpath, "input", "NGSPICE_INPUT_DIR");
+        tfree(ngpath);
     }
 #else
     NG_IGNORE(argv0);

src/misc/util.c

@@ -193,15 +193,10 @@ basename(const char *name)
 char *
 ngdirname(const char *name)
 {
-    static char *ret = NULL;
+    char *ret;
     const char *end = NULL;
     int start = 0;
 
-    if (ret) {
-        free(ret);
-        ret = NULL;
-    }
-
     if(name && ((name[0] >= 'a' && name[0] <= 'z') ||
                 (name[0] >= 'A' && name[0] <= 'Z')) && name[1] == ':')
         start = 2;
@@ -237,14 +232,9 @@ ngdirname(const char *name)
 char *
 ngdirname(const char *name)
 {
-    static char *ret = NULL;
+    char *ret;
     const char *end;
 
-    if (ret) {
-        free(ret);
-        ret = NULL;
-    }
-
     end = name ? strrchr(name, '/') : NULL;
 
     if(end && end == name)