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社区首页 >问答首页 >为什么这个V8/Javascript代码表现这么差?

为什么这个V8/Javascript代码表现这么差?
EN

Stack Overflow用户
提问于 2011-08-11 11:48:10
回答 1查看 2.9K关注 0票数 11

我一直在研究一些有趣的编程基准测试,以了解与其他语言相比,node.js的性能如何:http://benchmarksgame.alioth.debian.org/u32/compare.php?lang=node&lang2=php

虽然结果主要是处理通常使用C或Fortran变体解决的算法问题,但是有一个测试对于V8来说非常糟糕:

位位-52 x比慢

由于v8在所有其他测试中的整体性能都优于PHP,所以我认为代码有问题,或者是某些特定于V8/Javascript实现的错误,使得它的性能非常糟糕。那是什么?

代码1: V8

代码语言:javascript
运行
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// The Computer Language Benchmarks Game
//  http://shootout.alioth.debian.org
//
//  Contributed by Matthew Wilson 
//  biginteger derived from Tom Wu's jsbn.js


var compareTo, multiply, divide, addTo, add, intValue, shiftLeft, nbv;

function main($n) {
  var $i=1, $s="", $d, neg10=nbv(-10), three=nbv(3), ten=nbv(10), g = 1, $g,
  digits=Array(10), $z0=nbv(1), $z1=nbv(0), $z2=nbv(1), negdigits=Array(10),
  k = 0, $k, l = 2, $l, a;

  for(var i=0; i<10; ++i) { negdigits[i] = multiply(digits[i] = nbv(i),neg10) }

  do {
    while ( compareTo($z0,$z2) > 0
         || ($d = intValue(divide(add(multiply($z0,three),$z1),$z2))) != 
             intValue(divide(add(shiftLeft($z0,2),$z1),$z2))
    ) {
      $z1 = multiply($z1,$g = nbv(g+=2));
      $z2 = multiply($z2,$g);
      addTo($z1, multiply($z0,$l = nbv(l+=4)), $z1);
      $z0 = multiply($z0,$k = nbv(++k));
    }
    $z0 = multiply($z0,ten);
    $z1 = multiply($z1,ten);
    addTo($z1, multiply($z2,negdigits[$d]), $z1);
    $s += $d;

    if ($i % 10 == 0) { print($s+"\t:"+$i); $s="" }
  } while (++$i <= $n)

  if (($i = $n % 10) != 0) { $s += Array(11-$i).join(' ') }
  if ($s.length > 0) { print($s+"\t:"+$n) }
}

var functions;
load('/home/dunham/shootout/bench/Include/javascript/biginteger.js');

compareTo=functions[0];
multiply=functions[1];
divide=functions[2];
addTo=functions[3];
add=functions[4];
nbv=functions[5];
shiftLeft=functions[6];
intValue=functions[7];

main.call(this, 1*arguments[0]*1)

代码2: PHP

代码语言:javascript
运行
复制
<?php /* The Great Computer Language Shootout 
   http://shootout.alioth.debian.org/
   contributed by Isaac Gouy 
   php -q pidigits.php 27
*/

class Transformation {
   var $q, $r, $s, $t, $k;

   function Transformation($q, $r, $s, $t){
      $this->q = $q;
      $this->r = $r;      
      $this->s = $s;
      $this->t = $t;               
   }

   function Unity(){
      return new Transformation("1", "0", "0", "1");              
   }   

   function Zero(){
      return new Transformation("0", "0", "0", "0");              
   }      

   function Compose($a){
      $qq = bcmul($this->q, $a->q);
      $qrrt = bcadd(bcmul($this->q, $a->r), bcmul($this->r, $a->t));
      $sqts = bcadd(bcmul($this->s, $a->q), bcmul($this->t, $a->s));
      $srtt = bcadd(bcmul($this->s, $a->r), bcmul($this->t, $a->t));   
      return new Transformation($qq, $qrrt, $sqts, $srtt);
   }

   function Extract($j){
      $bigj = strval($j);
      $qjr = bcadd(bcmul($this->q, $bigj), $this->r);
      $sjt = bcadd(bcmul($this->s, $bigj), $this->t);
      $d = bcdiv($qjr, $sjt);
      return floor($d);
   }

   function Next(){ 
      $this->k = $this->k + 1;
      $this->q = strval($this->k);
      $this->r = strval(4*$this->k + 2);
      $this->s = "0";
      $this->t = strval(2*$this->k + 1);
      return $this;      
   }                
}

class PiDigitStream {
   var $z, $x, $inverse;

   function PiDigitStream(){
      $this->z = Transformation::Unity();
      $this->x = Transformation::Zero();      
      $this->inverse = Transformation::Zero();   
   }

   function Produce($j){
      $i = $this->inverse;
      $i->q = "10";
      $i->r = strval(-10*$j);
      $i->s = "0";
      $i->t = "1";
      return $i->Compose($this->z);
   }   

   function Consume($a){
      return $this->z ->Compose($a);  
   }

   function Digit(){
      return $this->z ->Extract(3);  
   }  

   function IsSafe($j){
      return $j == ($this->z ->Extract(4));  
   }    

   function Next(){
      $y = $this->Digit();
      if ($this->IsSafe($y)){
         $this->z = $this->Produce($y);
         return $y;
      } else {
         $this->z = $this->Consume($this->x ->Next());
         return $this->Next();      
      }
   } 
}


$n = $argv[1];
$i = 0;
$length = 10;
$pidigit = new PiDigitStream;

while ($n > 0){
   if ($n < $length){
      for ($j=0; $j<$n; $j++) printf("%d",$pidigit->Next());
      for ($j=$n; $j<$length; $j++)  print " ";
      $i += $n;
   } else {
      for ($j=0; $j<$length; $j++) printf("%d",$pidigit->Next());
      $i += $length;   
   }
   print "\t:$i\n";
   $n -= $length;
}
?>
EN

回答 1

Stack Overflow用户

发布于 2012-05-29 19:23:37

出于好奇,我使用节点-bigint (包装libgmp)编写了另一个版本。我将最快的C执行情况与基准测试的版本进行了比较。性能正如您所期望的那样,与使用libgmp的其他语言实现类似。

结果

C(用gcc -pipe -Wall -O3编译-fomit-框架-指针pidigits.c -o pi位表-lgmp)

代码语言:javascript
运行
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./pidigits-c 10000  1.11s user 0.00s system 99% cpu 1.116 total

节点(0.6.18)

代码语言:javascript
运行
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node pidigits-gmp.js 10000  3.61s user 3.15s system 100% cpu 6.712 total

来源

代码语言:javascript
运行
复制
var bigint = require('bigint');

function calculatePi(N) {
  var i = 0,
      k = 0,
      k1 = 1,
      ns = 0,

      a = bigint(0),
      d = bigint(1),
      m = bigint(0),
      n = bigint(1),
      t = bigint(0),
      u = bigint(0);

  while (1) {
    k += 1;
    k1 += 2;
    t = n.shiftLeft(1);
    n = n.mul(k);
    a = a.add(t).mul(k1);
    d = d.mul(k1);

    if (a.cmp(n) >= 0) {
      m = n.mul(3).add(a);
      t = m.div(d);
      u = m.mod(d).add(n);

      if (d.cmp(u) > 0) {
        ns = ns * 10 + t.toNumber();
        i += 1;

        if (i % 10 === 0) {
          console.log(ns + '\t:' + i);
          ns = 0;
        }

        if (i >= N) break;

        a = a.sub(d.mul(t)).mul(10);
        n = n.mul(10);
      }
    }
  }
}

calculatePi(process.argv[2] || 10);
票数 3
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页面原文内容由Stack Overflow提供。腾讯云小微IT领域专用引擎提供翻译支持
原文链接:

https://stackoverflow.com/questions/7025286

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