Convert round doubles to fixnums instead of floats (#349)

* Convert round doubles to fixnums instead of floats

Fixes: #348

* squash! tweak for large numbers

Author: bnoordhuis

ext/mini_racer_extension/mini_racer_extension.c

@@ -1,8 +1,10 @@
 #include <stdatomic.h>
+#include <stdint.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
 #include <pthread.h>
+#include <math.h>
 
 #include "ruby.h"
 #include "ruby/encoding.h"
@@ -282,7 +284,11 @@ static void des_int(void *arg, int64_t v)
 
 static void des_num(void *arg, double v)
 {
-    put(arg, DBL2NUM(v));
+    if (isfinite(v) && v == trunc(v) && v >= INT64_MIN && v <= INT64_MAX) {
+        put(arg, LONG2FIX(v));
+    } else {
+        put(arg, DBL2NUM(v));
+    }
 }
 
 static void des_date(void *arg, double v)

test/mini_racer_test.rb

@@ -1144,4 +1144,14 @@ def test_termination_exception
     a.kill
     b.kill
   end
+
+  def test_large_integer
+    [10_000_000_001, -2**63, 2**63-1].each { |big_int|
+      context = MiniRacer::Context.new
+      context.attach("test", proc { big_int })
+      result = context.eval("test()")
+      assert_equal(result.class, big_int.class)
+      assert_equal(result, big_int)
+    }
+  end
 end