1 files changed, 49 insertions, 0 deletions
diff --git a/grammars/c/disambiguate.c b/grammars/c/disambiguate.c
new file mode 100644
index 0000000..9a8bf08
--- /dev/null
+++ b/grammars/c/disambiguate.c
@@ -0,0 +1,49 @@
+int disambiguator(struct state *old, struct state *new) {
+    // printf("Old tree: ");
+    // print_parse_tree2(old);
+    // printf("New tree: ");
+    // print_parse_tree2(new);
+
+    if (old->start_idx != new->start_idx) {
+        // printf("\t\tIGNORING "); print_parse_tree2(old);
+        // printf("\t\tVS:      "); print_parse_tree2(new);
+        return 2;
+    }
+
+    // Prefer the earlier parsings in the grammar when two entirely different
+    // productions are taken.
+    if (old->production_id != new->production_id)
+        return old->production_id < new->production_id
+             ? 0 : 1;
+
+    // If they're the same production ...
+    prod_id_t prod = old->production_id;
+    if (PRODUCTION_ID_TO_SYMBOL[prod] == SYMBOL_EXPR) {
+        if (PRODUCTION_ID_TO_PRODUCTION[prod][1] == SYMBOL_OP) {
+            struct token *old_tok = find_token(old, 1),
+                         *new_tok = find_token(new, 1);
+            char *old_s = old_tok->string, *new_s = new_tok->string;
+            const char *precedence[] = {".", "->", "*", "/", "%", "+", "-",
+                "<<", ">>", "<", "<=", ">", ">=", "==", "!=", "&", "|", "&&",
+                "||", "=", "+=", "-=", "*=", "/=", "%=", "<<=", ">>=", "&=",
+                "^=", "|=", ",", 0};
+            if (strcmp(old_s, new_s)) {
+                for (const char **p = precedence; *p; p++) {
+                    if (!strcmp(old_s, *p)) {
+                        return 1;
+                    } else if (!strcmp(new_s, *p)) {
+                        return 0;
+                    }
+                }
+                // BAD!
+                return 2;
+            } else {
+                // Associate RIGHT
+                if (old_tok < new_tok)      return 1;
+                else if (old_tok > new_tok) return 0;
+            }
+        }
+    }
+    printf("TOTALLY UNKNOWN!\n");
+    return 2;
+}