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, 42 insertions, 0 deletions

diff --git a/lib/buffer.js b/lib/buffer.js
index b138552ef9..2fe13303f6 100644
--- a/lib/buffer.js
+++ b/lib/buffer.js
@@ -17,6 +17,48 @@ var poolSize, poolOffset, allocPool;
 
 
 binding.setupBufferJS(Buffer.prototype, bindingObj);
+
+const swap16n = binding.swap16;
+const swap32n = binding.swap32;
+
+function swap(b, n, m) {
+  const i = b[n];
+  b[n] = b[m];
+  b[m] = i;
+}
+
+Buffer.prototype.swap16 = function swap16() {
+  // For Buffer.length < 512, it's generally faster to
+  // do the swap in javascript. For larger buffers,
+  // dropping down to the native code is faster.
+  const len = this.length;
+  if (len % 2 !== 0)
+    throw new RangeError('Buffer size must be a multiple of 16-bits');
+  if (len < 512) {
+    for (var i = 0; i < len; i += 2)
+      swap(this, i, i + 1);
+    return this;
+  }
+  return swap16n.apply(this);
+};
+
+Buffer.prototype.swap32 = function swap32() {
+  // For Buffer.length < 1024, it's generally faster to
+  // do the swap in javascript. For larger buffers,
+  // dropping down to the native code is faster.
+  const len = this.length;
+  if (len % 4 !== 0)
+    throw new RangeError('Buffer size must be a multiple of 32-bits');
+  if (len < 1024) {
+    for (var i = 0; i < len; i += 4) {
+      swap(this, i, i + 3);
+      swap(this, i + 1, i + 2);
+    }
+    return this;
+  }
+  return swap32n.apply(this);
+};
+
 const flags = bindingObj.flags;
 const kNoZeroFill = 0;