Add isSafeInteger to test if a Long can be safely represented as a JS number

Author: dcodeIO

README.md

@@ -187,6 +187,9 @@ API
 * Long#**isPositive**(): `boolean`<br />
   Tests if this Long's value is positive or zero.
 
+* Long#**isSafeInteger**(): `boolean`<br />
+  Tests if this Long can be safely represented as a JavaScript number.
+
 * Long#**isZero**/**eqz**(): `boolean`<br />
   Tests if this Long's value equals zero.
 

index.js

@@ -645,6 +645,22 @@ LongPrototype.getNumBitsAbs = function getNumBitsAbs() {
   return this.high != 0 ? bit + 33 : bit + 1;
 };
 
+/**
+ * Tests if this Long can be safely represented as a JavaScript number.
+ * @this {!Long}
+ * @returns {boolean}
+ */
+LongPrototype.isSafeInteger = function isSafeInteger() {
+  // 2^53-1 is the maximum safe value
+  var top11Bits = this.high >> 21;
+  // [0, 2^53-1]
+  if (!top11Bits) return true;
+  // > 2^53-1
+  if (this.unsigned) return false;
+  // [-2^53, -1] except -2^53
+  return top11Bits === -1 && !(this.low === 0 && this.high === -0x200000);
+};
+
 /**
  * Tests if this Long's value equals zero.
  * @this {!Long}

tests/index.js

@@ -232,6 +232,19 @@ var tests = [ // BEGIN TEST CASES
       var signedFromUnsigned = Long.fromBigInt(values[i].unsigned);
       assert.strictEqual(signedFromUnsigned.toBigInt(), values[i].signed);
     }
+  },
+
+  function testSafeInteger() {
+    assert(Long.fromNumber(0).isSafeInteger());
+    assert(Long.fromNumber(1).isSafeInteger());
+    assert(Long.fromNumber(-1).isSafeInteger());
+    assert(!Long.fromNumber(-1).toUnsigned().isSafeInteger());
+    assert(Long.fromNumber(Math.pow(2, 32)).isSafeInteger());
+    assert(Long.fromNumber(-Math.pow(2, 32)).isSafeInteger());
+    assert(Long.fromNumber(Math.pow(2, 53) - 1).isSafeInteger());
+    assert(Long.fromNumber(-Math.pow(2, 53) + 1).isSafeInteger());
+    assert(!Long.fromNumber(Math.pow(2, 53)).isSafeInteger());
+    assert(!Long.fromNumber(-Math.pow(2, 53)).isSafeInteger());
   }
 
 ]; // END TEST CASES

types.d.ts

@@ -225,6 +225,11 @@ export declare class Long {
    */
   isPositive(): boolean;
 
+  /**
+   * Tests if this Long can be safely represented as a JavaScript number.
+   */
+  isSafeInteger(): boolean;
+
   /**
    * Tests if this Long's value equals zero.
    */