Generate asn_constant.h

Currently, there is no code generated for following ASN.1 excerpt.
Thus application is not aware of these values.

    maxnoofErrors           INTEGER ::= 256
    maxnoofBPLMNs           INTEGER ::= 6
    maxnoofPLMNsPerMME      INTEGER ::= 32
    maxnoofEPLMNs           INTEGER ::= 15
    ...

This commit generate asn_constant.h which has the following macro
defitions :

    #define maxnoofErrors (256)
    #define maxnoofBPLMNs (6)
    #define maxnoofPLMNsPerMME (32)
    #define maxnoofEPLMNs (15)
    #define maxnoofEPLMNsPlusOne (16)
    ...

It only handles ASN_BASIC_INTEGER type. Other built-in types shall
be added in the future.

libasn1compiler/asn1c_save.c

@@ -54,6 +54,7 @@ static int pdu_collection_has_unused_types(arg_t *arg);
 static const char *generate_pdu_C_definition(void);
 static void asn1c__cleanup_pdu_type(void);
 static int asn1c__pdu_type_lookup(const char *typename);
+static int generate_constant_file(arg_t *arg, const char *destdir);
 
 static int
 asn1c__save_library_makefile(arg_t *arg, const asn1c_dep_chainset *deps,
@@ -436,6 +437,8 @@ asn1c_save_compiled_output(arg_t *arg, const char *datadir, const char *destdir,
     asn1c_dep_chainset_free(deps);
     asn1c__cleanup_pdu_type();
 
+    generate_constant_file(arg, destdir);
+
     return ret;
 }
 
@@ -944,3 +947,49 @@ include_type_to_pdu_collection(arg_t *arg) {
 
     return 0;
 }
+
+static abuf *
+generate_constant_collection(arg_t *arg) {
+    asn1p_module_t *mod;
+    abuf *buf = abuf_new();
+
+    abuf_printf(buf, "/*\n * Generated by asn1c-" VERSION
+                     " (http://lionet.info/asn1c)\n */\n\n");
+    abuf_printf(buf, "#ifndef _ASN_CONSTANT_H\n#define _ASN_CONSTANT_H\n\n");
+
+    abuf_printf(buf, "#ifdef __cplusplus\nextern \"C\" {\n#endif\n\n");
+
+    TQ_FOR(mod, &(arg->asn->modules), mod_next) {
+        TQ_FOR(arg->expr, &(mod->members), next) {
+            if(arg->expr->meta_type != AMT_VALUE)
+                continue;
+
+            if(arg->expr->expr_type == ASN_BASIC_INTEGER) {
+                abuf_printf(buf, "#define %s (%s)\n",
+                            asn1c_make_identifier(0, arg->expr, 0),
+                            asn1p_itoa(arg->expr->value->value.v_integer));
+            }
+        }
+    }
+
+    abuf_printf(buf, "\n\n#ifdef __cplusplus\n}\n#endif\n\n#endif /* _ASN_CONSTANT_H */\n");
+    return buf;
+}
+
+static int
+generate_constant_file(arg_t *arg, const char *destdir) {
+    abuf *buf = generate_constant_collection(arg);
+    assert(buf);
+
+    FILE *fp = asn1c_open_file(destdir, "asn_constant", ".h", 0);
+    if(fp == NULL) {
+        perror("asn_constant.h");
+        return -1;
+    }
+    safe_fwrite(buf->buffer, buf->length, 1, fp);
+    fclose(fp);
+    abuf_free(buf);
+
+    safe_fprintf(stderr, "Generated asn_constant.h\n");
+    return 0;
+}