fix mishandling of ^ inside an expression

Makefile

@@ -101,6 +101,7 @@ test: all
 	@$(PYTHON) ./scripts/regex_test_neg.py [012345-9]             $(NRAND_TESTS)
 	@$(PYTHON) ./scripts/regex_test_neg.py [0-56789]              $(NRAND_TESTS)
 	@$(PYTHON) ./scripts/regex_test_neg.py .*123faerdig           $(NRAND_TESTS)
+	@$(PYTHON) ./scripts/regex_test_neg.py a^                     $(NRAND_TESTS)
 	@echo
 	@echo
 	@./tests/test2

re.c

@@ -393,6 +393,7 @@ static int matchone(regex_t p, char c)
     case NOT_ALPHA:      return !matchalphanum(c);
     case WHITESPACE:     return  matchwhitespace(c);
     case NOT_WHITESPACE: return !matchwhitespace(c);
+    case BEGIN:          return 0;
     default:             return  (p.u.ch == c);
   }
 }

tests/test1.c

@@ -101,11 +101,12 @@ int main()
     int should_fail;
     int length;
     int correctlen;
-    size_t ntests = sizeof(test_vector) / sizeof(*test_vector);
+    size_t nvector_tests = sizeof(test_vector) / sizeof(*test_vector);
+    size_t ntests = nvector_tests + 1;
     size_t nfailed = 0;
     size_t i;
 
-    for (i = 0; i < ntests; ++i)
+    for (i = 0; i < nvector_tests; ++i)
     {
         pattern = test_vector[i][1];
         text = test_vector[i][2];
@@ -141,6 +142,21 @@ int main()
         }
     }
 
+    // regression test for unhandled BEGIN in the middle of an expression
+    // we need to test text strings with all possible values for the second
+    // byte because re.c was matching it against an uninitalized value, so
+    // it could be anything
+    pattern = "a^";
+    for (i = 0; i < 255; i++) {
+      char text_buf[] = { 'a', i, '\0' };
+      int m = re_match(pattern, text_buf, &length);
+      if (m != -1) {
+        fprintf(stderr, "[%lu/%lu]: pattern '%s' matched '%s' unexpectedly", ntests, ntests, pattern, text_buf);
+        nfailed += 1;
+        break;
+      }
+    }
+
     // printf("\n");
     printf("%lu/%lu tests succeeded.\n", ntests - nfailed, ntests);
     printf("\n");