buffer: add swap16() and swap32() methods

Adds Buffer.prototype.swap16() and Buffer.prototype.swap32()
methods that mutate the Buffer instance in-place by swapping the
16-bit and 32-bit byte-order.

Example:

```js
const buf = Buffer([0x1, 0x2, 0x3, 0x4]);
buf.swap16();
console.log(buf);
  // prints Buffer(0x2, 0x1, 0x4, 0x3);

buf.swap32();
console.log(buf);
  // prints Buffer(0x3, 0x4, 0x1, 0x2);
```

PR-URL: https://github.com/nodejs/node/pull/5724
Reviewed-By: Trevor Norris <trev.norris@gmail.com>

1 files changed, 61 insertions, 0 deletions

diff --git a/benchmark/buffers/buffer-swap.js b/benchmark/buffers/buffer-swap.js
new file mode 100644
index 0000000000..4ff9a23d41
--- /dev/null
+++ b/benchmark/buffers/buffer-swap.js
@@ -0,0 +1,61 @@
+'use strict';
+
+const common = require('../common.js');
+
+const bench = common.createBenchmark(main, {
+  method: ['swap16', 'swap32', 'htons', 'htonl'],
+  len: [4, 64, 512, 768, 1024, 1536, 2056, 4096, 8192],
+  n: [1e6]
+});
+
+// The htons and htonl methods below are used to benchmark the
+// performance difference between doing the byteswap in pure
+// javascript regardless of Buffer size as opposed to dropping
+// down to the native layer for larger Buffer sizes.
+
+Buffer.prototype.htons = function htons() {
+  if (this.length % 2 !== 0)
+    throw new RangeError();
+  for (var i = 0, n = 0; i < this.length; i += 2) {
+    n = this[i];
+    this[i] = this[i + 1];
+    this[i + 1] = n;
+  }
+  return this;
+};
+
+Buffer.prototype.htonl = function htonl() {
+  if (this.length % 2 !== 0)
+    throw new RangeError();
+  for (var i = 0, n = 0; i < this.length; i += 4) {
+    n = this[i];
+    this[i] = this[i + 3];
+    this[i + 3] = n;
+    n = this[i + 1];
+    this[i + 1] = this[i + 2];
+    this[i + 2] = n;
+  }
+  return this;
+};
+
+function createBuffer(len) {
+  const buf = Buffer.allocUnsafe(len);
+  for (var i = 1; i <= len; i++)
+    buf[i - 1] = i;
+  return buf;
+}
+
+function bufferSwap(n, buf, method) {
+  for (var i = 1; i <= n; i++)
+    buf[method]();
+}
+
+function main(conf) {
+  const method = conf.method;
+  const len = conf.len | 0;
+  const n = conf.n | 0;
+  const buf = createBuffer(len);
+  bench.start();
+  bufferSwap(n, buf, method);
+  bench.end(n);
+}