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buffer: add swap16() and swap32() methods
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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: #5724
Reviewed-By: Trevor Norris <trev.norris@gmail.com>
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jasnell committed Mar 23, 2016
1 parent 443c2d5 commit 7d73e60
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61 changes: 61 additions & 0 deletions benchmark/buffers/buffer-swap.js
Original file line number Diff line number Diff line change
@@ -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);
}
36 changes: 36 additions & 0 deletions doc/api/buffer.markdown
Original file line number Diff line number Diff line change
Expand Up @@ -1245,6 +1245,42 @@ buf.slice(-5, -2).toString();
// Returns 'uff', equivalent to buf.slice(1, 4)
```

### buf.swap16()

* Return: {Buffer}

Interprets the `Buffer` as an array of unsigned 16-bit integers and swaps
the byte-order *in-place*. Throws a `RangeError` if the `Buffer` length is
not a multiple of 16 bits. The method returns a reference to the Buffer, so
calls can be chained.

```js
const buf = Buffer.from([0x1, 0x2, 0x3, 0x4, 0x5, 0x6, 0x7, 0x8]);
console.log(buf);
// Prints Buffer(0x1, 0x2, 0x3, 0x4, 0x5, 0x6, 0x7, 0x8)
buf.swap16();
console.log(buf);
// Prints Buffer(0x2, 0x1, 0x4, 0x3, 0x6, 0x5, 0x8, 0x7)
```

### buf.swap32()

* Return: {Buffer}

Interprets the `Buffer` as an array of unsigned 32-bit integers and swaps
the byte-order *in-place*. Throws a `RangeError` if the `Buffer` length is
not a multiple of 32 bits. The method returns a reference to the Buffer, so
calls can be chained.

```js
const buf = Buffer.from([0x1, 0x2, 0x3, 0x4, 0x5, 0x6, 0x7, 0x8]);
console.log(buf);
// Prints Buffer(0x1, 0x2, 0x3, 0x4, 0x5, 0x6, 0x7, 0x8)
buf.swap32();
console.log(buf);
// Prints Buffer(0x4, 0x3, 0x2, 0x1, 0x8, 0x7, 0x6, 0x5)
```

### buf.toString([encoding[, start[, end]]])

* `encoding` {String} Default: `'utf8'`
Expand Down
42 changes: 42 additions & 0 deletions lib/buffer.js
Original file line number Diff line number Diff line change
Expand Up @@ -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;

Expand Down
32 changes: 32 additions & 0 deletions src/node_buffer.cc
Original file line number Diff line number Diff line change
Expand Up @@ -51,6 +51,13 @@
#define BUFFER_MALLOC(length) \
zero_fill_all_buffers ? calloc(length, 1) : malloc(length)

#define SWAP_BYTES(arr, a, b) \
do { \
const uint8_t lo = arr[a]; \
arr[a] = arr[b]; \
arr[b] = lo; \
} while (0)

namespace node {

// if true, all Buffer and SlowBuffer instances will automatically zero-fill
Expand Down Expand Up @@ -1092,6 +1099,28 @@ void IndexOfNumber(const FunctionCallbackInfo<Value>& args) {
: -1);
}

void Swap16(const FunctionCallbackInfo<Value>& args) {
Environment* env = Environment::GetCurrent(args);
THROW_AND_RETURN_UNLESS_BUFFER(env, args.This());
SPREAD_ARG(args.This(), ts_obj);

for (size_t i = 0; i < ts_obj_length; i += 2) {
SWAP_BYTES(ts_obj_data, i, i + 1);
}
args.GetReturnValue().Set(args.This());
}

void Swap32(const FunctionCallbackInfo<Value>& args) {
Environment* env = Environment::GetCurrent(args);
THROW_AND_RETURN_UNLESS_BUFFER(env, args.This());
SPREAD_ARG(args.This(), ts_obj);

for (size_t i = 0; i < ts_obj_length; i += 4) {
SWAP_BYTES(ts_obj_data, i, i + 3);
SWAP_BYTES(ts_obj_data, i + 1, i + 2);
}
args.GetReturnValue().Set(args.This());
}

// pass Buffer object to load prototype methods
void SetupBufferJS(const FunctionCallbackInfo<Value>& args) {
Expand Down Expand Up @@ -1158,6 +1187,9 @@ void Initialize(Local<Object> target,
env->SetMethod(target, "writeFloatBE", WriteFloatBE);
env->SetMethod(target, "writeFloatLE", WriteFloatLE);

env->SetMethod(target, "swap16", Swap16);
env->SetMethod(target, "swap32", Swap32);

target->Set(env->context(),
FIXED_ONE_BYTE_STRING(env->isolate(), "kMaxLength"),
Integer::NewFromUnsigned(env->isolate(), kMaxLength)).FromJust();
Expand Down
60 changes: 60 additions & 0 deletions test/parallel/test-buffer-swap.js
Original file line number Diff line number Diff line change
@@ -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);

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