buffer: optimize readDouble and readFloat methods
Compute the floating point number in JavaScript to avoid having to call
out to the C++ runtime. The improvements are not insubstantial:
improvement confidence p.value
value="big" endian="BE" type="Double" noAssert="false" 292.86 % *** 1.688367e-08
value="big" endian="BE" type="Double" noAssert="true" 353.19 % *** 6.079414e-10
value="big" endian="BE" type="Float" noAssert="false" 406.21 % *** 1.730122e-07
value="big" endian="BE" type="Float" noAssert="true" 450.81 % *** 6.909242e-07
value="big" endian="LE" type="Double" noAssert="false" 268.39 % *** 8.625486e-09
value="big" endian="LE" type="Double" noAssert="true" 310.66 % *** 2.798332e-15
value="big" endian="LE" type="Float" noAssert="false" 382.99 % *** 3.412057e-07
value="big" endian="LE" type="Float" noAssert="true" 394.60 % *** 1.406742e-07
value="inf" endian="BE" type="Double" noAssert="false" 312.91 % *** 7.407943e-12
value="inf" endian="BE" type="Double" noAssert="true" 392.47 % *** 3.821179e-08
value="inf" endian="BE" type="Float" noAssert="false" 466.01 % *** 8.953363e-08
value="inf" endian="BE" type="Float" noAssert="true" 460.76 % *** 5.381256e-09
value="inf" endian="LE" type="Double" noAssert="false" 279.50 % *** 2.390682e-09
value="inf" endian="LE" type="Double" noAssert="true" 335.30 % *** 3.587173e-09
value="inf" endian="LE" type="Float" noAssert="false" 439.77 % *** 1.057133e-07
value="inf" endian="LE" type="Float" noAssert="true" 426.72 % *** 4.353408e-09
value="nan" endian="BE" type="Double" noAssert="false" 271.18 % *** 2.281526e-05
value="nan" endian="BE" type="Double" noAssert="true" 312.63 % *** 1.974975e-07
value="nan" endian="BE" type="Float" noAssert="false" 429.17 % *** 2.416228e-07
value="nan" endian="BE" type="Float" noAssert="true" 461.39 % *** 1.956714e-08
value="nan" endian="LE" type="Double" noAssert="false" 267.03 % *** 9.938479e-12
value="nan" endian="LE" type="Double" noAssert="true" 276.93 % *** 7.842481e-08
value="nan" endian="LE" type="Float" noAssert="false" 415.97 % *** 8.082710e-07
value="nan" endian="LE" type="Float" noAssert="true" 433.68 % *** 1.030200e-07
value="small" endian="BE" type="Double" noAssert="false" 273.20 % *** 9.071652e-11
value="small" endian="BE" type="Double" noAssert="true" 326.25 % *** 3.120167e-08
value="small" endian="BE" type="Float" noAssert="false" 845.61 % *** 8.044170e-08
value="small" endian="BE" type="Float" noAssert="true" 868.61 % *** 2.944539e-08
value="small" endian="LE" type="Double" noAssert="false" 251.29 % *** 5.613930e-09
value="small" endian="LE" type="Double" noAssert="true" 286.82 % *** 8.149603e-10
value="small" endian="LE" type="Float" noAssert="false" 824.87 % *** 1.199729e-08
value="small" endian="LE" type="Float" noAssert="true" 834.35 % *** 4.799620e-08
value="zero" endian="BE" type="Double" noAssert="false" 216.70 % *** 3.872293e-12
value="zero" endian="BE" type="Double" noAssert="true" 239.31 % *** 6.439601e-09
value="zero" endian="BE" type="Float" noAssert="false" 353.75 % *** 3.639974e-07
value="zero" endian="BE" type="Float" noAssert="true" 388.86 % *** 7.074318e-10
value="zero" endian="LE" type="Double" noAssert="false" 179.34 % *** 5.230763e-06
value="zero" endian="LE" type="Double" noAssert="true" 199.66 % *** 2.177589e-11
value="zero" endian="LE" type="Float" noAssert="false" 299.55 % *** 9.961978e-08
value="zero" endian="LE" type="Float" noAssert="true" 333.30 % *** 2.470764e-08
PR-URL: https://github.com/nodejs/node/pull/17775
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
This commit is contained in:
Ben Noordhuis
Anna Henningsen
parent
cb3de880be
commit
df30fd586d
46
benchmark/buffers/buffer-read-float.js
Normal file
46
benchmark/buffers/buffer-read-float.js
Normal file
@ -0,0 +1,46 @@
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'use strict';
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const common = require('../common.js');
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const bench = common.createBenchmark(main, {
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noAssert: ['false', 'true'],
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type: ['Double', 'Float'],
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endian: ['BE', 'LE'],
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value: ['zero', 'big', 'small', 'inf', 'nan'],
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millions: [1]
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});
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function main(conf) {
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const noAssert = conf.noAssert === 'true';
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const len = +conf.millions * 1e6;
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const buff = Buffer.alloc(8);
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const type = conf.type || 'Double';
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const endian = conf.endian;
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const fn = `read${type}${endian}`;
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const values = {
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Double: {
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zero: 0,
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big: 2 ** 1023,
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small: 2 ** -1074,
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inf: Infinity,
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nan: NaN,
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},
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Float: {
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zero: 0,
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big: 2 ** 127,
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small: 2 ** -149,
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inf: Infinity,
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nan: NaN,
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},
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};
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const value = values[type][conf.value];
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buff[`write${type}${endian}`](value, 0, noAssert);
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const testFunction = new Function('buff', `
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for (var i = 0; i !== ${len}; i++) {
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buff.${fn}(0, ${JSON.stringify(noAssert)});
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}
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`);
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bench.start();
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testFunction(buff);
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bench.end(len / 1e6);
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}
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@ -31,10 +31,6 @@ const {
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indexOfBuffer,
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indexOfNumber,
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indexOfString,
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readDoubleBE: _readDoubleBE,
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readDoubleLE: _readDoubleLE,
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readFloatBE: _readFloatBE,
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readFloatLE: _readFloatLE,
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swap16: _swap16,
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swap32: _swap32,
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swap64: _swap64,
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@ -1201,35 +1197,80 @@ Buffer.prototype.readInt32BE = function readInt32BE(offset, noAssert) {
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};
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Buffer.prototype.readFloatLE = function readFloatLE(offset, noAssert) {
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offset = offset >>> 0;
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if (!noAssert)
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checkOffset(offset, 4, this.length);
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return _readFloatLE(this, offset);
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// For the casual reader who has not at the current time memorized the
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// IEEE-754 standard in full detail: floating point numbers consist of
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// a fraction, an exponent and a sign bit: 23+8+1 bits for single precision
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// numbers and 52+11+1 bits for double precision numbers.
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//
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// A zero exponent is either a positive or negative zero, if the fraction
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// is zero, or a denormalized number when it is non-zero. Multiplying the
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// fraction by the smallest possible denormal yields the denormalized number.
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//
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// An all-bits-one exponent is either a positive or negative infinity, if
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// the fraction is zero, or NaN when it is non-zero. The standard allows
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// both quiet and signalling NaNs but since NaN is a canonical value in
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// JavaScript, we cannot (and do not) distinguish between the two.
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//
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// Other exponents are regular numbers and are computed by subtracting the bias
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// from the exponent (127 for single precision, 1023 for double precision),
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// yielding an exponent in the ranges -126-127 and -1022-1024 respectively.
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//
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// Of interest is that the fraction of a normal number has an extra bit of
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// precision that is not stored but is reconstructed by adding one after
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// multiplying the fraction with the result of 2**-bits_in_fraction.
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function toDouble(x0, x1) {
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const frac = x0 + 0x100000000 * (x1 & 0xFFFFF);
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const expt = (x1 >>> 20) & 2047;
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const sign = (x1 >>> 31) ? -1 : 1;
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if (expt === 0) {
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if (frac === 0) return sign * 0;
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return sign * frac * 2 ** -1074;
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} else if (expt === 2047) {
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if (frac === 0) return sign * Infinity;
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return NaN;
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}
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return sign * 2 ** (expt - 1023) * (1 + frac * 2 ** -52);
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}
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function toFloat(x) {
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const frac = x & 0x7FFFFF;
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const expt = (x >>> 23) & 255;
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const sign = (x >>> 31) ? -1 : 1;
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if (expt === 0) {
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if (frac === 0) return sign * 0;
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return sign * frac * 2 ** -149;
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} else if (expt === 255) {
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if (frac === 0) return sign * Infinity;
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return NaN;
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}
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return sign * 2 ** (expt - 127) * (1 + frac * 2 ** -23);
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}
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Buffer.prototype.readDoubleBE = function(offset, noAssert) {
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const x1 = this.readUInt32BE(offset + 0, noAssert);
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const x0 = this.readUInt32BE(offset + 4, noAssert);
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return toDouble(x0, x1);
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};
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Buffer.prototype.readFloatBE = function readFloatBE(offset, noAssert) {
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offset = offset >>> 0;
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if (!noAssert)
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checkOffset(offset, 4, this.length);
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return _readFloatBE(this, offset);
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Buffer.prototype.readDoubleLE = function(offset, noAssert) {
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const x0 = this.readUInt32LE(offset + 0, noAssert);
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const x1 = this.readUInt32LE(offset + 4, noAssert);
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return toDouble(x0, x1);
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};
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Buffer.prototype.readDoubleLE = function readDoubleLE(offset, noAssert) {
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offset = offset >>> 0;
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if (!noAssert)
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checkOffset(offset, 8, this.length);
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return _readDoubleLE(this, offset);
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Buffer.prototype.readFloatBE = function(offset, noAssert) {
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return toFloat(this.readUInt32BE(offset, noAssert));
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};
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Buffer.prototype.readDoubleBE = function readDoubleBE(offset, noAssert) {
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offset = offset >>> 0;
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if (!noAssert)
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checkOffset(offset, 8, this.length);
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return _readDoubleBE(this, offset);
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Buffer.prototype.readFloatLE = function(offset, noAssert) {
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return toFloat(this.readUInt32LE(offset, noAssert));
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};
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@ -719,49 +719,6 @@ static inline void Swizzle(char* start, unsigned int len) {
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}
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template <typename T, enum Endianness endianness>
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void ReadFloatGeneric(const FunctionCallbackInfo<Value>& args) {
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THROW_AND_RETURN_UNLESS_BUFFER(Environment::GetCurrent(args), args[0]);
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SPREAD_BUFFER_ARG(args[0], ts_obj);
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uint32_t offset = args[1]->Uint32Value();
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CHECK_LE(offset + sizeof(T), ts_obj_length);
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union NoAlias {
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T val;
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char bytes[sizeof(T)];
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};
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union NoAlias na;
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const char* ptr = static_cast<const char*>(ts_obj_data) + offset;
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memcpy(na.bytes, ptr, sizeof(na.bytes));
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if (endianness != GetEndianness())
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Swizzle(na.bytes, sizeof(na.bytes));
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args.GetReturnValue().Set(na.val);
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}
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void ReadFloatLE(const FunctionCallbackInfo<Value>& args) {
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ReadFloatGeneric<float, kLittleEndian>(args);
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}
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void ReadFloatBE(const FunctionCallbackInfo<Value>& args) {
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ReadFloatGeneric<float, kBigEndian>(args);
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}
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void ReadDoubleLE(const FunctionCallbackInfo<Value>& args) {
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ReadFloatGeneric<double, kLittleEndian>(args);
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}
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void ReadDoubleBE(const FunctionCallbackInfo<Value>& args) {
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ReadFloatGeneric<double, kBigEndian>(args);
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}
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template <typename T, enum Endianness endianness>
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void WriteFloatGeneric(const FunctionCallbackInfo<Value>& args) {
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Environment* env = Environment::GetCurrent(args);
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@ -1276,11 +1233,6 @@ void Initialize(Local<Object> target,
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env->SetMethod(target, "indexOfNumber", IndexOfNumber);
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env->SetMethod(target, "indexOfString", IndexOfString);
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env->SetMethod(target, "readDoubleBE", ReadDoubleBE);
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env->SetMethod(target, "readDoubleLE", ReadDoubleLE);
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env->SetMethod(target, "readFloatBE", ReadFloatBE);
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env->SetMethod(target, "readFloatLE", ReadFloatLE);
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env->SetMethod(target, "writeDoubleBE", WriteDoubleBE);
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env->SetMethod(target, "writeDoubleLE", WriteDoubleLE);
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env->SetMethod(target, "writeFloatBE", WriteFloatBE);
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