Issue #4: nextPrime should return prime > input, even if input is prime

bower.json

@@ -1,7 +1,7 @@
 {
   "name": "crunch",
   "main": "crunch.js",
-  "version": "1.0.4",
+  "version": "1.0.5",
   "homepage": "https://github.com/vukicevic/crunch",
   "authors": [
     "Nenad Vukicevic <vukicevic@gmail.com>"

crunch.js

@@ -618,13 +618,26 @@ function Crunch(rawIn, rawOut) {
     return mrb(x, 3);
   }
 
-  function npr(x) {
+  /**
+   * Quick add integer n to arbitrary precision integer x avoiding overflow
+   */
+  function qad(x, n) {
     var l = x.length - 1;
 
-    x[l] |= 1;
+    if (x[l] + n < 268435456) {
+      x[l] += n;
+    } else {
+      x = add(x, [n]);
+    }
+
+    return x;
+  }
+
+  function npr(x) {
+    x = qad(x, 1 + x[x.length-1] % 2);
 
     while (!tpr(x)) {
-      x[l] = (x[l]+2) % 268435456; //backwards on boundary
+      x = qad(x, 2);
     }
 
     return x;

package.json

@@ -1,6 +1,6 @@
 {
   "name": "number-crunch",
-  "version": "1.0.4",
+  "version": "1.0.5",
   "description": "Fast arbitraty-precision integer arithmetic library. Used for large-number calculations including finding large prime numbers, performing modular exponentiation and other arithmetic operations.",
   "main": "crunch.js",
   "scripts": {

test/crunch.js

@@ -369,11 +369,14 @@ describe('#next prime', function() {
     crunch.nextPrime([5, 57, 84, 76, 233, 0, 120, 91, 180, 180, 8]).should.eql([5, 57, 84, 76, 233, 0, 120, 91, 180, 180, 107]);
   });
   it('Find next prime', function() {
-    crunch.nextPrime([17]).should.eql([17]);
+    crunch.nextPrime([17]).should.eql([19]);
   });
   it('Find next prime', function() {
     crunch.nextPrime([7, 200]).should.eql([7, 201]);
   });
+  it('Find next prime', function() {
+    crunch.nextPrime([3]).should.eql([5]);
+  });
 });
 
 describe('#factorial', function() {