Add a utility function to the d_cosim code model to open dynamic

libraries. It automatically tries adding standard file extensions,
so that model lines for d_cosim can be the same for all OSs.

src/include/ngspice/cosim.h

@@ -62,7 +62,7 @@ struct co_info {
 
     void          (*out_fn)(struct co_info *, unsigned int, Digital_t *);
     void           *handle;        // Co-simulator's private handle
-    volatile double          vtime;         // Time in the co-simulation.
+    volatile double vtime;         // Time in the co-simulation.
     Cosim_method    method;        // May be set in Cosim_setup;
 
     /* Arguments for the co-simulator shim and the simulation itself
@@ -73,6 +73,10 @@ struct co_info {
     int             sim_argc;
     const char    * const * const lib_argv;
     const char    * const * const sim_argv;
+
+    /* Utility function for access to dynamic libraries. */
+
+    void         *(*dlopen_fn)(const char *fn);
 };
 
 extern void  Cosim_setup(struct co_info *pinfo); // This must exist.

src/xspice/icm/digital/d_cosim/cfunc.mod

@@ -39,13 +39,15 @@ char *dlerror(void) // Lifted from dev.c.
     if (rc == 0) { /* FormatMessage failed */
         (void) sprintf(errstr, errstr_fmt, (unsigned long) GetLastError());
     } else {
-        snprintf(errstr, sizeof errstr, "%s", lpMsgBuf);
+        snprintf(errstr, sizeof errstr, "%s", (char *)lpMsgBuf);
         LocalFree(lpMsgBuf);
     }
     return errstr;
 } /* end of function dlerror */
 #else
 #include <dlfcn.h>
+#include <unistd.h>
+#include <fcntl.h>
 #endif
 
 #include "ngspice/cosim.h"
@@ -109,6 +111,60 @@ static void callback(ARGS, Mif_Callback_Reason_t reason)
     }
 }
 
+/* A utility function used to open static libraries, trying an installation
+ * directory and different file extenstions.
+ */
+
+#if defined (__MINGW32__) || defined (__CYGWIN__) || defined (_MSC_VER)
+#include <io.h>
+
+static const char *exts[] = { "", ".so", ".DLL", NULL};
+#define CMPFN _stricmp // Ignores case.
+#define TESTFN(f) (_access(f, 4) == 0) // Checks for read access.
+#define SLIBFILE "DLL"
+#ifndef NGSPICELIBDIR
+#define NGSPICELIBDIR "C:\\Spice64\\lib\\ngspice" // Defined by configure?
+#endif
+
+#else
+
+static const char *exts[] = { "", ".so", NULL};
+#define CMPFN strcmp
+#define TESTFN(f) (access(f, R_OK) == 0)
+#define SLIBFILE "shared library"
+#endif
+#define FLAGS  (RTLD_GLOBAL | RTLD_NOW)
+
+static void *cosim_dlopen(const char *fn)
+{
+    const char **xp;
+    size_t       l1, l2;
+    void        *handle;
+    char         path[2048];
+
+    l1 = strlen(fn);
+    for (xp = exts; *xp; xp++) {
+        l2 = strlen(*xp);
+        if (l2 && l1 > l2 && !CMPFN(*xp, fn + l1 - l2))
+            continue; // Extension already present
+        snprintf(path, sizeof path, "%s%s", fn, *xp);
+        handle = dlopen(path, FLAGS);
+        if (handle)
+            return handle;
+        if (TESTFN(path))       // File exists.
+            break;
+        snprintf(path, sizeof path,  NGSPICELIBDIR "/%s%s", fn, *xp);
+        handle = dlopen(path, FLAGS);
+        if (handle)
+            return handle;
+        if (TESTFN(path))
+            break;
+    }
+
+    fprintf(stderr, "Cannot open " SLIBFILE " %s: %s\n", path, dlerror());
+    return NULL;
+}
+
 /* Function called when a co-simulator output changes.
  * Out-of-range values for bit_num must be ignored.
  */
@@ -409,11 +465,9 @@ void ucm_d_cosim(ARGS)
         /* Load the shared library containing the co-simulator. */
 
         fn = PARAM(simulation);
-        handle = dlopen(fn, RTLD_GLOBAL | RTLD_NOW);
+        handle = cosim_dlopen(fn);
         if (!handle) {
-            cm_message_send("Failed to load simulation binary. "
-                            "Try setting LD_LIBRARY_PATH.");
-            cm_message_send(dlerror());
+            cm_message_send("d_cosim failed to load simulation binary.");
             return;
         }
         ifp = (void (*)(struct co_info *))dlsym(handle, "Cosim_setup");
@@ -432,6 +486,7 @@ void ucm_d_cosim(ARGS)
         ip->so_handle = handle;
         ip->info.vtime = 0.0;
         ip->info.out_fn = accept_output;
+        ip->info.dlopen_fn = cosim_dlopen;
         CALLBACK = callback;
 
 	if (PARAM_NULL(lib_args)) {

src/xspice/verilog/icarus_shim.c

@@ -285,15 +285,10 @@ void Cosim_setup(struct co_info *pinfo)
     if (pinfo->lib_argc > 0 && pinfo->lib_argv[0][0]) // Explicit path to VVP?
         file = (char *)pinfo->lib_argv[0];
     else //libvvp is assumed to be in the OS search path.
-#if defined(__MINGW32__) || defined(_MSC_VER)
-        file = "libvvp.DLL";
-#else
-        file = "libvvp.so";
-#endif
-    context->vvp_handle = dlopen(file, RTLD_GLOBAL | RTLD_NOW);
+        file = "libvvp";
+    context->vvp_handle = pinfo->dlopen_fn(file);
     if (!context->vvp_handle) {
-        fprintf(stderr, "Icarus shim failed to load VVP library: %s.\n",
-                dlerror());
+        fprintf(stderr, "Icarus shim failed to load VVP library\n");
         abort();
     }