#100 Add Decimal.sum method

decimal.js

@@ -2629,9 +2629,9 @@
    */
   function cosine(Ctor, x) {
     var k, len, y;
-    
+
     if (x.isZero()) return x;
-    
+
     // Argument reduction: cos(4x) = 8*(cos^4(x) - cos^2(x)) + 1
     // i.e. cos(x) = 8*(cos^4(x/4) - cos^2(x/4)) + 1
 
@@ -3665,10 +3665,10 @@
   function sine(Ctor, x) {
     var k,
       len = x.d.length;
-    
+
     if (len < 3) {
       return x.isZero() ? x : taylorSeries(Ctor, 2, x, x);
-    }  
+    }
 
     // Argument reduction: sin(5x) = 16*sin^5(x) - 20*sin^3(x) + 5*sin(x)
     // i.e. sin(x) = 16*sin^5(x/5) - 20*sin^3(x/5) + 5*sin(x/5)
@@ -3959,6 +3959,7 @@
    *  sinh
    *  sqrt
    *  sub
+   *  sum
    *  tan
    *  tanh
    *  trunc
@@ -4407,6 +4408,7 @@
     Decimal.sinh = sinh;          // ES6
     Decimal.sqrt = sqrt;
     Decimal.sub = sub;
+    Decimal.sum = sum;
     Decimal.tan = tan;
     Decimal.tanh = tanh;          // ES6
     Decimal.trunc = trunc;        // ES6
@@ -4801,6 +4803,28 @@
   }
 
 
+  /*
+   * Return a new Decimal whose value is the sum of the arguments, rounded to `precision`
+   * significant digits using rounding mode `rounding`.
+   *
+   * Only the result is rounded, not the intermediate calculations.
+   *
+   * arguments {number|string|Decimal}
+   *
+   */
+  function sum() {
+    var i = 0,
+      args = arguments,
+      x = new this(args[i]);
+
+    external = false;
+    for (; x.s && ++i < args.length;) x = x.plus(args[i]);
+    external = true;
+
+    return finalise(x, this.precision, this.rounding);
+  }
+
+
   /*
    * Return a new Decimal whose value is the tangent of `x`, rounded to `precision` significant
    * digits using rounding mode `rounding`.