helpers: power of two related functions added

royaltm · Sep 30, 2019 · 30bac22 · 30bac22
1 parent c9e7edf
commit 30bac22
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Showing 2 changed files with 81 additions and 1 deletion.
diff --git a/lib/utils/helpers.js b/lib/utils/helpers.js
@@ -304,3 +304,31 @@ exports.validateIntegerOption = function(options, name, min, max) {
   if (max !== undefined && value > max) throw new TypeError(`options.${name} must be <= ${max}`);
   return value;
 };
+
+/**
+ * Returns `true` if the num is a power of two in the range of [1, 2^32].
+ *
+ * @param {number} num
+ * @return {bool} 
+**/
+exports.isPowerOfTwo32 = function(num) {
+  return (num - 1) >>> 0 === (num - 1) && num !== 0 && !(num & (num - 1))
+};
+
+/**
+ * Returns the next power of two in the range of [1, 2^31]. Otherwise returns 0.
+ *
+ * @param {number} num
+ * @return {number} 
+**/
+exports.nextPowerOfTwo32 = function(num) {
+  num = num >> 0;
+  num--;
+  num |= num >> 1;
+  num |= num >> 2;
+  num |= num >> 4;
+  num |= num >> 8;
+  num |= num >> 16;
+  num++;
+  return num;
+};
diff --git a/test/utils/test.helpers.js b/test/utils/test.helpers.js
@@ -1,5 +1,5 @@
 /* 
- *  Copyright (c) 2016-2018 Rafał Michalski <[email protected]>
+ *  Copyright (c) 2016-2019 Rafał Michalski <[email protected]>
  *  License: LGPL
  */
 "use strict";
@@ -337,3 +337,55 @@ test('validateIntegerOption', t => {
   t.throws(() => helpers.validateIntegerOption({foo: '100'}, 'foo', null, 99), new TypeError("options.foo must be <= 99"));
   t.end();
 });
+
+test('isPowerOfTwo32', t => {
+  t.strictEquals(helpers.isPowerOfTwo32(), false);
+  t.strictEquals(helpers.isPowerOfTwo32([]), false);
+  t.strictEquals(helpers.isPowerOfTwo32({}), false);
+  t.strictEquals(helpers.isPowerOfTwo32(null), false);
+  t.strictEquals(helpers.isPowerOfTwo32(0), false);
+  t.strictEquals(helpers.isPowerOfTwo32(1), true);
+  t.strictEquals(helpers.isPowerOfTwo32(-1), false);
+  var res = [];
+  for (let v = -65536; v <= 65536; ++v) {
+    if (helpers.isPowerOfTwo32(v)) {
+      res.push(v);
+    }
+  }
+  t.strictSame(res, [1,2,4,8,16,32,64,128,256,512,1024,2048,4096,8192,16384,32768,65536]);
+  t.strictEquals(helpers.isPowerOfTwo32(16777215), false);
+  t.strictEquals(helpers.isPowerOfTwo32(16777216), true);
+  t.strictEquals(helpers.isPowerOfTwo32(16777217), false);
+  t.strictEquals(helpers.isPowerOfTwo32(2**31+1), false);
+  t.strictEquals(helpers.isPowerOfTwo32(2**31), true);
+  t.strictEquals(helpers.isPowerOfTwo32(2**31-1), false);
+  t.strictEquals(helpers.isPowerOfTwo32(2**32), true);
+  t.strictEquals(helpers.isPowerOfTwo32(2**32-1), false);
+  t.end();
+});
+
+test('nextPowerOfTwo32', t => {
+  var res = new Map();
+  t.strictEquals(helpers.nextPowerOfTwo32(), 0);
+  t.strictEquals(helpers.nextPowerOfTwo32([]), 0);
+  t.strictEquals(helpers.nextPowerOfTwo32({}), 0);
+  t.strictEquals(helpers.nextPowerOfTwo32(null), 0);
+  t.strictEquals(helpers.nextPowerOfTwo32(0), 0);
+  t.strictEquals(helpers.nextPowerOfTwo32(-1), 0);
+  t.strictEquals(helpers.nextPowerOfTwo32(1), 1);
+  t.strictEquals(helpers.nextPowerOfTwo32(2), 2);
+  t.strictEquals(helpers.nextPowerOfTwo32(3), 4);
+  t.strictEquals(helpers.nextPowerOfTwo32(4), 4);
+  for (let x = -65536; x <= 65536; ++x) {
+    let y = helpers.nextPowerOfTwo32(x);
+    res.set(y, (res.get(y)||0) + 1);
+  }
+  t.strictSame(Array.from(res.keys()), [0,1,2,4,8,16,32,64,128,256,512,1024,2048,4096,8192,16384,32768,65536]);
+  t.strictSame(Array.from(res.values()), [65537,1,1,2,4,8,16,32,64,128,256,512,1024,2048,4096,8192,16384,32768]);
+  t.strictEquals(helpers.nextPowerOfTwo32(2**31+1), 0);
+  t.strictEquals(helpers.nextPowerOfTwo32(2**31), 0x80000000);
+  t.strictEquals(helpers.nextPowerOfTwo32(2**31-1), 0x80000000);
+  t.strictEquals(helpers.nextPowerOfTwo32(2**32), 0);
+  t.strictEquals(helpers.nextPowerOfTwo32(2**32-1), 0);
+  t.end();
+});