lib: fix for negative numbers: imuln, modrn, idivn

indutny · Jun 18, 2018 · e69c617 · e69c617
1 parent 8963ee9
commit e69c617
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Showing 2 changed files with 25 additions and 3 deletions.
diff --git a/lib/bn.js b/lib/bn.js
@@ -1915,6 +1915,9 @@
  };
 
  BN.prototype.imuln = function imuln (num) {
+ var isNegNum = num < 0;
+ if (isNegNum) num = -num;
+
  assert(typeof num === 'number');
  assert(num < 0x4000000);
 
@@ -1935,7 +1938,7 @@
  this.length++;
  }
 
- return this;
+ return isNegNum ? this.ineg() : this;
  };
 
  BN.prototype.muln = function muln (num) {
@@ -2481,6 +2484,9 @@
  };
 
  BN.prototype.modrn = function modrn (num) {
+ var isNegNum = num < 0;
+ if (isNegNum) num = -num;
+
  assert(num <= 0x3ffffff);
  var p = (1 << 26) % num;
 
@@ -2489,7 +2495,7 @@
  acc = (p * acc + (this.words[i] | 0)) % num;
  }
 
- return acc;
+ return isNegNum ? -acc : acc;
  };
 
  // WARNING: DEPRECATED
@@ -2499,6 +2505,9 @@
 
  // In-place division by number
  BN.prototype.idivn = function idivn (num) {
+ var isNegNum = num < 0;
+ if (isNegNum) num = -num;
+
  assert(num <= 0x3ffffff);
 
  var carry = 0;
@@ -2508,7 +2517,8 @@
  carry = w % num;
  }
 
- return this._strip();
+ this._strip();
+ return isNegNum ? this.ineg() : this;
  };
 
  BN.prototype.divn = function divn (num) {

diff --git a/test/arithmetic-test.js b/test/arithmetic-test.js
@@ -290,6 +290,16 @@ describe('BN.js/Arithmetic', function () {
  new BN(0).imuln(0x4000000);
  }, /^Error: Assertion failed$/);
  });
+
+ it('should negate number if number is negative', function () {
+ var a = new BN('dead', 16);
+ assert.equal(a.clone().imuln(-1).toString(16), a.clone().neg().toString(16));
+ assert.equal(a.clone().muln(-1).toString(16), a.clone().neg().toString(16));
+
+ var b = new BN('dead', 16);
+ 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));
+ });
  });
 
  describe('.pow()', function () {
@@ -392,6 +402,7 @@ describe('BN.js/Arithmetic', function () {
  describe('.idivn()', function () {
  it('should divide numbers in-place', function () {
  assert.equal(new BN('10', 16).idivn(3).toString(16), '5');
+ assert.equal(new BN('10', 16).idivn(-3).toString(16), '-5');
  assert.equal(new BN('12', 16).idivn(3).toString(16), '6');
  assert.equal(new BN('10000000000000000').idivn(3).toString(10),
  '3333333333333333');
@@ -530,6 +541,7 @@ describe('BN.js/Arithmetic', function () {
  describe('.modrn()', function () {
  it('should act like .mod() on small numbers', function () {
  assert.equal(new BN('10', 16).modrn(256).toString(16), '10');
+ assert.equal(new BN('10', 16).modrn(-256).toString(16), '-10');
  assert.equal(new BN('100', 16).modrn(256).toString(16), '0');
  assert.equal(new BN('1001', 16).modrn(256).toString(16), '1');
  assert.equal(new BN('100000000001', 16).modrn(256).toString(16), '1');