From be0e7e02d2d5f4e49c792e3e46a88e0c760f071a Mon Sep 17 00:00:00 2001
From: Christopher Jeffrey <chjjeffrey@gmail.com>
Date: Sat, 17 Jun 2017 18:19:12 -0700
Subject: [PATCH] util: add isSafeAddition.

---
 lib/utils/util.js | 21 +++++++++++++++++++++
 1 file changed, 21 insertions(+)

diff --git a/lib/utils/util.js b/lib/utils/util.js
index e98ff10b..aebb15f5 100644
--- a/lib/utils/util.js
+++ b/lib/utils/util.js
@@ -200,6 +200,14 @@ if (Object.assign)
 
 util.MAX_SAFE_INTEGER = 0x1fffffffffffff;
 
+/**
+ * Max safe addition (52 bits).
+ * @const {Number}
+ * @default
+ */
+
+util.MAX_SAFE_ADDITION = 0xfffffffffffff;
+
 /**
  * Test whether a number is below MAX_SAFE_INTEGER.
  * @param {Number} value
@@ -210,6 +218,19 @@ util.isSafeInteger = function isSafeInteger(value) {
   return value >= -0x1fffffffffffff && value <= 0x1fffffffffffff;
 };
 
+/**
+ * Test whether the result of a positive
+ * addition would be below MAX_SAFE_INTEGER.
+ * @param {Number} value
+ * @returns {Boolean}
+ */
+
+util.isSafeAddition = function isSafeAddition(a, b) {
+  assert(a >= 0);
+  assert(b >= 0);
+  return a <= util.MAX_SAFE_ADDITION && b <= util.MAX_SAFE_ADDITION;
+};
+
 /**
  * Test whether a number is Number,
  * finite, and below MAX_SAFE_INTEGER.