fix iaddn sign issue (#216)

When we add number to BN instance and this number equal to number in BN instance with negative value we should receive zero with lack of sign.
indutny · Jul 7, 2019 · 44650ad · 44650ad
1 parent 8a8d9ba
commit 44650ad
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diff --git a/lib/bn.js b/lib/bn.js
@@ -2160,7 +2160,7 @@
 
     // Possible sign change
     if (this.negative !== 0) {
-      if (this.length === 1 && (this.words[0] | 0) < num) {
+      if (this.length === 1 && (this.words[0] | 0) <= num) {
         this.words[0] = num - (this.words[0] | 0);
         this.negative = 0;
         return this;

diff --git a/test/arithmetic-test.js b/test/arithmetic-test.js
@@ -83,6 +83,11 @@ describe('BN.js/Arithmetic', function () {
         new BN(0).iaddn(0x4000000);
       }, /^Error: Assertion failed$/);
     });
+
+    it('should reset sign if value equal to value in instance', function () {
+      var a = new BN(-1);
+      assert.equal(a.addn(1).toString(), '0');
+    });
   });
 
   describe('.sub()', function () {