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, 60 insertions, 0 deletions

diff --git a/test/parallel/test-buffer-swap.js b/test/parallel/test-buffer-swap.js
new file mode 100644
index 0000000000..c2a6901955
--- /dev/null
+++ b/test/parallel/test-buffer-swap.js
@@ -0,0 +1,60 @@
+'use strict';
+
+require('../common');
+const assert = require('assert');
+
+const buf = Buffer.from([0x1, 0x2, 0x3, 0x4]);
+
+assert.strictEqual(buf, buf.swap16());
+assert.deepStrictEqual(buf, Buffer.from([0x2, 0x1, 0x4, 0x3]));
+
+assert.strictEqual(buf, buf.swap32());
+assert.deepStrictEqual(buf, Buffer.from([0x3, 0x4, 0x1, 0x2]));
+
+const buf_array = [];
+for (var i = 1; i < 33; i++)
+  buf_array.push(i);
+const buf2 = Buffer.from(buf_array);
+buf2.swap32();
+assert.deepStrictEqual(buf2,
+    Buffer.from([0x04, 0x03, 0x02, 0x01, 0x08, 0x07, 0x06, 0x05, 0x0c,
+                 0x0b, 0x0a, 0x09, 0x10, 0x0f, 0x0e, 0x0d, 0x14, 0x13,
+                 0x12, 0x11, 0x18, 0x17, 0x16, 0x15, 0x1c, 0x1b, 0x1a,
+                 0x19, 0x20, 0x1f, 0x1e, 0x1d]));
+buf2.swap16();
+assert.deepStrictEqual(buf2,
+    Buffer.from([0x03, 0x04, 0x01, 0x02, 0x07, 0x08, 0x05, 0x06, 0x0b,
+                 0x0c, 0x09, 0x0a, 0x0f, 0x10, 0x0d, 0x0e, 0x13, 0x14,
+                 0x11, 0x12, 0x17, 0x18, 0x15, 0x16, 0x1b, 0x1c, 0x19,
+                 0x1a, 0x1f, 0x20, 0x1d, 0x1e]));
+
+const buf3 = Buffer.from([0x1, 0x2, 0x3, 0x4, 0x5, 0x6, 0x7]);
+buf3.slice(1, 5).swap32();
+assert.deepStrictEqual(buf3, Buffer.from([0x1, 0x5, 0x4, 0x3, 0x2, 0x6, 0x7]));
+
+buf3.slice(1, 5).swap16();
+assert.deepStrictEqual(buf3, Buffer.from([0x1, 0x4, 0x5, 0x2, 0x3, 0x6, 0x7]));
+
+// Force use of native code (Buffer size above threshold limit for js impl)
+const buf4 = Buffer.allocUnsafe(1024).fill([0x1, 0x2, 0x3, 0x4]);
+const buf5 = Buffer.allocUnsafe(1024).fill([0x2, 0x1, 0x4, 0x3]);
+const buf6 = Buffer.allocUnsafe(1024)
+                   .fill([0x1, 0x2, 0x3, 0x4, 0x5, 0x6, 0x7, 0x8]);
+const buf7 = Buffer.allocUnsafe(1024)
+                   .fill([0x4, 0x3, 0x2, 0x1, 0x8, 0x7, 0x6, 0x5]);
+
+buf4.swap16();
+assert.deepStrictEqual(buf4, buf5);
+
+buf6.swap32();
+assert.deepStrictEqual(buf6, buf7);
+
+
+const re16 = /Buffer size must be a multiple of 16-bits/;
+const re32 = /Buffer size must be a multiple of 32-bits/;
+
+assert.throws(() => Buffer.from(buf3).swap16(), re16);
+assert.throws(() => Buffer.alloc(1025).swap16(), re16);
+assert.throws(() => Buffer.from(buf3).swap32(), re32);
+assert.throws(() => buf3.slice(1, 3).swap32(), re32);
+assert.throws(() => Buffer.alloc(1025).swap32(), re32);