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buffer: improve {read,write}{U}Int* methods

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Increase the performance and simplify the logic of Buffer#write{U}Int*
and Buffer#read{U}Int* methods by placing the byte manipulation code
directly inline.

Also improve the speed of buffer-write benchmarks by creating a new
call directly to each method by using Function() instead of calling by
buff[fn].

Signed-off-by: Trevor Norris <trev.norris@gmail.com>

Conflicts:
	lib/buffer.js
This commit is contained in:
Nick Apperson 2014-03-25 09:51:13 -05:00 committed by Trevor Norris
parent 72dcc26c7a
commit ee95e4f5f7
3 changed files with 71 additions and 192 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

9
benchmark/buffers/buffer-read.js
View File

@ -20,9 +20,12 @@ function main(conf) {
var fn = 'read' + conf.type;
buff.writeDoubleLE(0, 0, noAssert);
var testFunction = new Function('buff', [
"for (var i = 0; i !== " + len + "; i++) {",
" buff." + fn + "(0, " + JSON.stringify(noAssert) + ");",
"}"
].join("\n"));
bench.start();
for (var i = 0; i < len; i++) {
buff[fn](0, noAssert);
}
testFunction(buff);
bench.end(len / 1e6);
}

24
benchmark/buffers/buffer-write.js
View File

@ -15,9 +15,9 @@ var bench = common.createBenchmark(main, {
const INT8 = 0x7f;
const INT16 = 0x7fff;
const INT32 = 0x7fffffff;
const UINT8 = INT8 * 2;
const UINT16 = INT16 * 2;
const UINT32 = INT32 * 2;
const UINT8 = (INT8 * 2) + 1;
const UINT16 = (INT16 * 2) + 1;
const UINT32 = INT32;
var mod = {
writeInt8: INT8,
@ -47,17 +47,23 @@ function main(conf) {
function benchInt(buff, fn, len, noAssert) {
var m = mod[fn];
var testFunction = new Function('buff', [
"for (var i = 0; i !== " + len + "; i++) {",
" buff." + fn + "(i & " + m + ", 0, " + JSON.stringify(noAssert) + ");",
"}"
].join("\n"));
bench.start();
for (var i = 0; i < len; i++) {
buff[fn](i % m, 0, noAssert);
}
testFunction(buff);
bench.end(len / 1e6);
}
function benchFloat(buff, fn, len, noAssert) {
var testFunction = new Function('buff', [
"for (var i = 0; i !== " + len + "; i++) {",
" buff." + fn + "(i, 0, " + JSON.stringify(noAssert) + ");",
"}"
].join("\n"));
bench.start();
for (var i = 0; i < len; i++) {
buff[fn](i * 0.1, 0, noAssert);
}
testFunction(buff);
bench.end(len / 1e6);
}

230
lib/buffer.js
View File

@ -590,113 +590,42 @@ Buffer.prototype.readUInt8 = function(offset, noAssert) {
};
function readUInt16(buffer, offset, isBigEndian) {
var val = 0;
if (isBigEndian) {
val = buffer[offset] << 8;
val |= buffer[offset + 1];
} else {
val = buffer[offset];
val |= buffer[offset + 1] << 8;
}
return val;
}
Buffer.prototype.readUInt16LE = function(offset, noAssert) {
if (!noAssert)
checkOffset(offset, 2, this.length);
return readUInt16(this, offset, false, noAssert);
return this[offset] | (this[offset + 1] << 8);
};
Buffer.prototype.readUInt16BE = function(offset, noAssert) {
if (!noAssert)
checkOffset(offset, 2, this.length);
return readUInt16(this, offset, true, noAssert);
return (this[offset] << 8) | this[offset + 1];
};
function readUInt32(buffer, offset, isBigEndian, noAssert) {
var val = 0;
if (isBigEndian) {
val = buffer[offset + 1] << 16;
val |= buffer[offset + 2] << 8;
val |= buffer[offset + 3];
val = val + (buffer[offset] << 24 >>> 0);
} else {
val = buffer[offset + 2] << 16;
val |= buffer[offset + 1] << 8;
val |= buffer[offset];
val = val + (buffer[offset + 3] << 24 >>> 0);
}
return val;
}
Buffer.prototype.readUInt32LE = function(offset, noAssert) {
if (!noAssert)
checkOffset(offset, 4, this.length);
return readUInt32(this, offset, false, noAssert);
return ((this[offset]) |
(this[offset + 1] << 8) |
(this[offset + 2] << 16)) +
(this[offset + 3] * 0x1000000);
};
Buffer.prototype.readUInt32BE = function(offset, noAssert) {
if (!noAssert)
checkOffset(offset, 4, this.length);
return readUInt32(this, offset, true, noAssert);
return (this[offset] * 0x1000000) +
((this[offset + 1] << 16) |
(this[offset + 2] << 8)) |
(this[offset + 3]);
};
/*
* Signed integer types, yay team! A reminder on how two's complement actually
* works. The first bit is the signed bit, i.e. tells us whether or not the
* number should be positive or negative. If the two's complement value is
* positive, then we're done, as it's equivalent to the unsigned representation.
*
* Now if the number is positive, you're pretty much done, you can just leverage
* the unsigned translations and return those. Unfortunately, negative numbers
* aren't quite that straightforward.
*
* At first glance, one might be inclined to use the traditional formula to
* translate binary numbers between the positive and negative values in two's
* complement. (Though it doesn't quite work for the most negative value)
* Mainly:
* - invert all the bits
* - add one to the result
*
* Of course, this doesn't quite work in Javascript. Take for example the value
* of -128. This could be represented in 16 bits (big-endian) as 0xff80. But of
* course, Javascript will do the following:
*
* > ~0xff80
* -65409
*
* Whoh there, Javascript, that's not quite right. But wait, according to
* Javascript that's perfectly correct. When Javascript ends up seeing the
* constant 0xff80, it has no notion that it is actually a signed number. It
* assumes that we've input the unsigned value 0xff80. Thus, when it does the
* binary negation, it casts it into a signed value, (positive 0xff80). Then
* when you perform binary negation on that, it turns it into a negative number.
*
* Instead, we're going to have to use the following general formula, that works
* in a rather Javascript friendly way. I'm glad we don't support this kind of
* weird numbering scheme in the kernel.
*
* (BIT-MAX - (unsigned)val + 1) * -1
*
* The astute observer, may think that this doesn't make sense for 8-bit numbers
* (really it isn't necessary for them). However, when you get 16-bit numbers,
* you do. Let's go back to our prior example and see how this will look:
*
* (0xffff - 0xff80 + 1) * -1
* (0x007f + 1) * -1
* (0x0080) * -1
*/
Buffer.prototype.readInt8 = function(offset, noAssert) {
if (!noAssert)
checkOffset(offset, 1, this.length);
@ -706,49 +635,41 @@ Buffer.prototype.readInt8 = function(offset, noAssert) {
};
function readInt16(buffer, offset, isBigEndian) {
var val = readUInt16(buffer, offset, isBigEndian);
if (!(val & 0x8000))
return val;
return (0xffff - val + 1) * -1;
}
Buffer.prototype.readInt16LE = function(offset, noAssert) {
if (!noAssert)
checkOffset(offset, 2, this.length);
return readInt16(this, offset, false);
var val = this[offset] | (this[offset + 1] << 8);
return (val & 0x8000) ? val | 0xFFFF0000 : val;
};
Buffer.prototype.readInt16BE = function(offset, noAssert) {
if (!noAssert)
checkOffset(offset, 2, this.length);
return readInt16(this, offset, true);
var val = this[offset + 1] | (this[offset] << 8);
return (val & 0x8000) ? val | 0xFFFF0000 : val;
};
function readInt32(buffer, offset, isBigEndian) {
var val = readUInt32(buffer, offset, isBigEndian);
if (!(val & 0x80000000))
return (val);
return (0xffffffff - val + 1) * -1;
}
Buffer.prototype.readInt32LE = function(offset, noAssert) {
if (!noAssert)
checkOffset(offset, 4, this.length);
return readInt32(this, offset, false);
return (this[offset]) |
(this[offset + 1] << 8) |
(this[offset + 2] << 16) |
(this[offset + 3] << 24);
};
Buffer.prototype.readInt32BE = function(offset, noAssert) {
if (!noAssert)
checkOffset(offset, 4, this.length);
return readInt32(this, offset, true);
return (this[offset] << 24) |
(this[offset + 1] << 16) |
(this[offset + 2] << 8) |
(this[offset + 3]);
};
Buffer.prototype.readFloatLE = function(offset, noAssert) {
@ -796,97 +717,42 @@ Buffer.prototype.writeUInt8 = function(value, offset, noAssert) {
};
function writeUInt16(buffer, value, offset, isBigEndian) {
if (isBigEndian) {
buffer[offset] = (value & 0xff00) >>> 8;
buffer[offset + 1] = value & 0x00ff;
} else {
buffer[offset + 1] = (value & 0xff00) >>> 8;
buffer[offset] = value & 0x00ff;
}
}
Buffer.prototype.writeUInt16LE = function(value, offset, noAssert) {
if (!noAssert)
checkInt(this, value, offset, 2, 0xffff, 0);
writeUInt16(this, value, offset, false);
this[offset] = value;
this[offset + 1] = (value >>> 8);
};
Buffer.prototype.writeUInt16BE = function(value, offset, noAssert) {
if (!noAssert)
checkInt(this, value, offset, 2, 0xffff, 0);
writeUInt16(this, value, offset, true);
this[offset] = (value >>> 8);
this[offset + 1] = value;
};
function writeUInt32(buffer, value, offset, isBigEndian) {
if (isBigEndian) {
buffer[offset] = (value >>> 24) & 0xff;
buffer[offset + 1] = (value >>> 16) & 0xff;
buffer[offset + 2] = (value >>> 8) & 0xff;
buffer[offset + 3] = value & 0xff;
} else {
buffer[offset + 3] = (value >>> 24) & 0xff;
buffer[offset + 2] = (value >>> 16) & 0xff;
buffer[offset + 1] = (value >>> 8) & 0xff;
buffer[offset] = value & 0xff;
}
}
Buffer.prototype.writeUInt32LE = function(value, offset, noAssert) {
if (!noAssert)
checkInt(this, value, offset, 4, 0xffffffff, 0);
writeUInt32(this, value, offset, false);
this[offset + 3] = (value >>> 24);
this[offset + 2] = (value >>> 16);
this[offset + 1] = (value >>> 8);
this[offset] = value;
};
Buffer.prototype.writeUInt32BE = function(value, offset, noAssert) {
if (!noAssert)
checkInt(this, value, offset, 4, 0xffffffff, 0);
writeUInt32(this, value, offset, true);
this[offset] = (value >>> 24);
this[offset + 1] = (value >>> 16);
this[offset + 2] = (value >>> 8);
this[offset + 3] = value;
};
/*
* We now move onto our friends in the signed number category. Unlike unsigned
* numbers, we're going to have to worry a bit more about how we put values into
* arrays. Since we are only worrying about signed 32-bit values, we're in
* slightly better shape. Unfortunately, we really can't do our favorite binary
* & in this system. It really seems to do the wrong thing. For example:
*
* > -32 & 0xff
* 224
*
* What's happening above is really: 0xe0 & 0xff = 0xe0. However, the results of
* this aren't treated as a signed number. Ultimately a bad thing.
*
* What we're going to want to do is basically create the unsigned equivalent of
* our representation and pass that off to the wuint* functions. To do that
* we're going to do the following:
*
* - if the value is positive
* we can pass it directly off to the equivalent wuint
* - if the value is negative
* we do the following computation:
* mb + val + 1, where
* mb is the maximum unsigned value in that byte size
* val is the Javascript negative integer
*
*
* As a concrete value, take -128. In signed 16 bits this would be 0xff80. If
* you do out the computations:
*
* 0xffff - 128 + 1
* 0xffff - 127
* 0xff80
*
* You can then encode this value as the signed version. This is really rather
* hacky, but it should work and get the job done which is our goal here.
*/
Buffer.prototype.writeInt8 = function(value, offset, noAssert) {
if (!noAssert)
checkInt(this, value, offset, 1, 0x7f, -0x80);
@ -898,32 +764,36 @@ Buffer.prototype.writeInt8 = function(value, offset, noAssert) {
Buffer.prototype.writeInt16LE = function(value, offset, noAssert) {
if (!noAssert)
checkInt(this, value, offset, 2, 0x7fff, -0x8000);
if (value < 0) value = 0xffff + value + 1;
writeUInt16(this, value, offset, false);
this[offset] = value;
this[offset + 1] = (value >>> 8);
};
Buffer.prototype.writeInt16BE = function(value, offset, noAssert) {
if (!noAssert)
checkInt(this, value, offset, 2, 0x7fff, -0x8000);
if (value < 0) value = 0xffff + value + 1;
writeUInt16(this, value, offset, true);
this[offset] = (value >>> 8);
this[offset + 1] = value;
};
Buffer.prototype.writeInt32LE = function(value, offset, noAssert) {
if (!noAssert)
checkInt(this, value, offset, 4, 0x7fffffff, -0x80000000);
if (value < 0) value = 0xffffffff + value + 1;
writeUInt32(this, value, offset, false);
this[offset] = value;
this[offset + 1] = (value >>> 8);
this[offset + 2] = (value >>> 16);
this[offset + 3] = (value >>> 24);
};
Buffer.prototype.writeInt32BE = function(value, offset, noAssert) {
if (!noAssert)
checkInt(this, value, offset, 4, 0x7fffffff, -0x80000000);
if (value < 0) value = 0xffffffff + value + 1;
writeUInt32(this, value, offset, true);
this[offset] = (value >>> 24);
this[offset + 1] = (value >>> 16);
this[offset + 2] = (value >>> 8);
this[offset + 3] = value;
};