Fix imuln/muln with zero (#313)

Co-authored-by: CanardMandarin <[email protected]>

Author: fanatid

.github/workflows/ci.yaml

@@ -16,7 +16,7 @@ jobs:
           fetch-depth: 1
 
       - name: Restore node_modules cache
-        uses: actions/cache@v1
+        uses: actions/cache@v4
         with:
           path: ~/.npm
           key: ${{ runner.os }}-node-${{ hashFiles('**/package.json') }}
@@ -37,7 +37,7 @@ jobs:
           fetch-depth: 1
 
       - name: Restore node_modules cache
-        uses: actions/cache@v1
+        uses: actions/cache@v4
         with:
           path: ~/.npm
           key: ${{ runner.os }}-node-${{ hashFiles('**/package.json') }}

lib/bn.js

@@ -2008,6 +2008,7 @@
       this.words[i] = carry;
       this.length++;
     }
+    this.length = num === 0 ? 1 : this.length;
 
     return isNegNum ? this.ineg() : this;
   };

test/arithmetic-test.js

@@ -305,6 +305,16 @@ describe('BN.js/Arithmetic', function () {
       assert.equal(b.clone().imuln(-42).toString(16), b.clone().neg().muln(42).toString(16));
       assert.equal(b.clone().muln(-42).toString(16), b.clone().neg().muln(42).toString(16));
     });
+
+    it('should strip length on zero multiplication', function () {
+      var a = new BN(42);
+      assert.equal(a.clone().imuln(0).isZero(), true);
+      assert.equal(a.clone().muln(0).isZero(), true);
+
+      var b = new BN('1222222225255589');
+      assert.equal(b.clone().imuln(0).isZero(), true);
+      assert.equal(b.clone().muln(0).isZero(), true);
+    });
   });
 
   describe('.pow()', function () {