这是为什么ocaml的计划比我的C程序更快吗？ [英] Why is this OCaml program faster than my C program?

问题描述

我写在C，Python和OCaml的一个基本 Hippity合计划。当然，这可能不是这三种语言的一个很好的标杆。但我得到的结果是这样的：

I wrote a basic Hippity Hop program in C, Python, and OCaml. Granted, this is probably not a very good benchmark of these three languages. But the results I got were something like this:

• 的Python：0.350秒


• C：0.050秒


• 的间preTED 的OCaml的：0.040秒


• 编译OCaml的：0.010

• Python: .350 seconds
• C: .050 seconds
• interpreted OCaml: .040 seconds
• compiled OCaml: .010

蟒蛇性能并没有真正让我感到吃惊，但我相当震惊在OCaml的有多快（尤其是跨preTED版本）。为了便于比较，我会后的C版本和OCaml的版本。

The python performance doesn't really surprise me, but I'm rather shocked at how fast the OCaml is (especially the interpreted version). For comparison, I'll post the C version and the OCaml version.

#include <stdio.h>
#include <stdlib.h>
#include <assert.h>

long get_count(char *name);

int main(int argc, char *argv[])
{
  if (argc != 2){
    printf("Filename must be specified as a positional argument.\n");
    exit(EXIT_FAILURE);
  }

  long count_no = get_count(argv[1]);

  int i;
  for (i = 1; i <= count_no; i++){
    if (((i % 3) == 0) && ((i % 5) == 0)){
      printf("Hop\n");
      continue;
    }
    if ((i % 3) == 0){
      printf("Hoppity\n");
    }
    if ((i % 5) == 0){
      printf("Hophop\n");
    }
  }
  return 0;
}

long get_count(char *name){
  FILE *fileptr = fopen(name, "r");
  if (!fileptr){
    printf("Unable to open file %s.\n", name);
    exit(EXIT_FAILURE);
  }
  size_t text_len = 20;
  char *file_text = calloc(text_len, sizeof(char));
  while (!feof(fileptr)){
    fread(file_text, sizeof(char), text_len, fileptr);
    assert(!ferror(fileptr));
    text_len += 20;
    file_text = realloc(file_text, text_len * sizeof(char));
  }
  long file_as_int = strtol(file_text, NULL, 10);

  free(file_text);
  return file_as_int;
}

的OCaml

open String;;

let trim str =
  if str = "" then "" else
  let search_pos init p next =
    let rec search i =
      if p i then raise(Failure "empty") else
      match str.[i] with
      | ' ' | '\n' | '\r' | '\t' -> search (next i)
      | _ -> i
    in
    search init
  in
  let len = String.length str in
  try
    let left = search_pos 0 (fun i -> i >= len) (succ)
    and right = search_pos (len - 1) (fun i -> i < 0) (pred)
    in
    String.sub str left (right - left + 1)
  with
  | Failure "empty" -> ""
;;

let rec iterate_over_numbers curr_num max_num =
  (
   if curr_num <= max_num then (
     if ((curr_num mod 3) == 0) && ((curr_num mod 5) == 0) then 
       print_endline "Hop"
     else if (curr_num mod 3) == 0 then 
       print_endline "Hoppity"
     else if (curr_num mod 5) == 0 then
       print_endline "Hophop";
     iterate_over_numbers (curr_num + 1) max_num
   ))
;;


let fname = Sys.argv.(1);;
let infile = open_in fname;;
let file_text = trim (input_line infile);;
close_in infile;;
let input_number = int_of_string file_text;;
iterate_over_numbers 1 input_number;;

不过我很好奇，想知道为什么我得到这些结果。我做我的C程序了愚蠢的事情，或者这只是一些OCaml的更快的？在我看来有些奇怪的是，一个跨preTED程序运行一点点比C版本速度更快，编译程序运行5倍的速度。

But I'm curious to know why I'm getting these results. Am I doing something dumb in my C program, or is this just something OCaml is faster at? It seems to me a bit strange that an interpreted program is running a little faster than the C version, and the compiled program is running 5 times as fast.

推荐答案

您C code不OCaml的code相当于 - 您使用否则，如果在OCaml中，以避免重新计算模量相当这么多。

Your C code isn't the equivalent of the OCaml code - you used 'else if' in the OCaml to avoid having to recompute moduli quite so much.

有在那读长整型一个可怕的很多code的。为什么不使用的fscanf（）;它会跳过空格和所有自动，避免你做的malloc（）等等。我不经常推荐使用的fscanf（），但是这看起来像它的设置 - 单行线，可能用空格两侧，没有有趣的东西。

There's an awful lot of code in that 'read the long integer'. Why not just use fscanf(); it skips blanks and all that automatically, and avoids you doing the malloc() etc. I don't often recommend using fscanf(), but this looks like a setup for it - a single line, possibly with spaces either side, no funny stuff.

---

好奇害死猫 - 但在这种情况下，不是豹

Curiosity killed the cat - but in this case, not the Leopard.

我下载的OCaml 3.11.1为MacOS X的英特尔和复制OCaml的code从问题到xxx.ml（OCaml的），并编译的成目标文件XXX（使用ocamlc -o XXX xxx.ml ）;我复制了C $ C $ç逐字到yyy.c和使用创造一个变种zzz.c 的fscanf（）和 FCLOSE（），并使用GCC -O -o YYY yyy.c和GCC -O -o ZZZ zzz.c编译它们。我创建了一个文件，文件3载： 987654 加一个换行符。我创建了一个shell脚本runthem.sh如图所示。需要注意的是'时间'是一个讨厌的命令，它认为它的输出必须到标准错误，即使你宁愿它没有 - 你必须工作挺难的，以到达你想要去的输出。 （范围命令，在给定范围内生成的数字，包容性的 - 因此，11％的计划值）

I downloaded OCaml 3.11.1 for MacOS X Intel and copied the OCaml code from the question into xxx.ml (OCaml), and compiled that into an object file xxx (using "ocamlc -o xxx xxx.ml"); I copied the C code verbatim into yyy.c and created a variant zzz.c using fscanf() and fclose(), and compiled them using "gcc -O -o yyy yyy.c" and "gcc -O -o zzz zzz.c". I created a file 'file3' containing: " 987654 " plus a newline. I created a shell script runthem.sh as shown. Note that 'time' is a pesky command that thinks its output must go to stderr even when you'd rather it didn't - you have to work quite hard to get the output where you want it to go. (The range command generates numbers in the given range, inclusive - hence 11 values per program.)

Osiris JL: cat runthem.sh
for prog in "ocaml xxx.ml" ./xxx ./yyy ./zzz
do
    for iter in $(range 0 10)
    do
    	r=$(sh -c "time $prog file3 >/dev/null" 2>&1)
    	echo $prog: $r
    done
done
Osiris JL:

我跑这一切都在一个现代的MacBook Pro（3 GHz的Core 2 Duo处理器等，4GB RAM）运行Leopard（10.5.8）。我得到的定时由图所示：

I ran all this on a modern MacBook Pro (3 GHz Core 2 Duo etc, 4GB RAM) running Leopard (10.5.8). The timings I got are shown by:

Osiris JL: sh runthem.sh
ocaml xxx.ml: real 0m0.961s user 0m0.524s sys 0m0.432s
ocaml xxx.ml: real 0m0.953s user 0m0.516s sys 0m0.430s
ocaml xxx.ml: real 0m0.959s user 0m0.517s sys 0m0.431s
ocaml xxx.ml: real 0m0.951s user 0m0.517s sys 0m0.430s
ocaml xxx.ml: real 0m0.952s user 0m0.516s sys 0m0.431s
ocaml xxx.ml: real 0m0.952s user 0m0.514s sys 0m0.431s
ocaml xxx.ml: real 0m0.951s user 0m0.515s sys 0m0.431s
ocaml xxx.ml: real 0m0.959s user 0m0.515s sys 0m0.431s
ocaml xxx.ml: real 0m0.950s user 0m0.515s sys 0m0.431s
ocaml xxx.ml: real 0m0.956s user 0m0.516s sys 0m0.431s
ocaml xxx.ml: real 0m0.952s user 0m0.514s sys 0m0.432s
./xxx: real 0m0.928s user 0m0.494s sys 0m0.430s
./xxx: real 0m0.938s user 0m0.494s sys 0m0.430s
./xxx: real 0m0.927s user 0m0.494s sys 0m0.430s
./xxx: real 0m0.928s user 0m0.492s sys 0m0.430s
./xxx: real 0m0.928s user 0m0.493s sys 0m0.430s
./xxx: real 0m0.927s user 0m0.493s sys 0m0.430s
./xxx: real 0m0.928s user 0m0.492s sys 0m0.430s
./xxx: real 0m0.933s user 0m0.497s sys 0m0.428s
./xxx: real 0m0.926s user 0m0.494s sys 0m0.429s
./xxx: real 0m0.921s user 0m0.492s sys 0m0.428s
./xxx: real 0m0.925s user 0m0.494s sys 0m0.428s
./yyy: real 0m0.027s user 0m0.026s sys 0m0.001s
./yyy: real 0m0.031s user 0m0.026s sys 0m0.002s
./yyy: real 0m0.028s user 0m0.026s sys 0m0.001s
./yyy: real 0m0.029s user 0m0.026s sys 0m0.002s
./yyy: real 0m0.028s user 0m0.026s sys 0m0.001s
./yyy: real 0m0.029s user 0m0.026s sys 0m0.002s
./yyy: real 0m0.028s user 0m0.026s sys 0m0.001s
./yyy: real 0m0.031s user 0m0.026s sys 0m0.002s
./yyy: real 0m0.028s user 0m0.026s sys 0m0.001s
./yyy: real 0m0.030s user 0m0.026s sys 0m0.002s
./yyy: real 0m0.028s user 0m0.026s sys 0m0.001s
./zzz: real 0m0.030s user 0m0.027s sys 0m0.002s
./zzz: real 0m0.029s user 0m0.027s sys 0m0.001s
./zzz: real 0m0.030s user 0m0.027s sys 0m0.002s
./zzz: real 0m0.029s user 0m0.027s sys 0m0.001s
./zzz: real 0m0.030s user 0m0.027s sys 0m0.002s
./zzz: real 0m0.029s user 0m0.027s sys 0m0.001s
./zzz: real 0m0.030s user 0m0.027s sys 0m0.002s
./zzz: real 0m0.029s user 0m0.027s sys 0m0.001s
./zzz: real 0m0.030s user 0m0.027s sys 0m0.002s
./zzz: real 0m0.029s user 0m0.027s sys 0m0.001s
./zzz: real 0m0.030s user 0m0.027s sys 0m0.002s
Osiris JL:

我没有看到OCaml的code运行比C code更快。我跑与文件中更小的数字被读取的试验，其结果有利于C $ C $的c进行类似

I don't see the OCaml code running faster than the C code. I ran the tests with smaller numbers in the file that was read, and the results were similarly in favour of the C code:

停止编号：345

ocaml xxx.ml: real 0m0.027s user 0m0.020s sys 0m0.005s
ocaml xxx.ml: real 0m0.021s user 0m0.016s sys 0m0.005s
ocaml xxx.ml: real 0m0.025s user 0m0.016s sys 0m0.004s
ocaml xxx.ml: real 0m0.020s user 0m0.015s sys 0m0.003s
ocaml xxx.ml: real 0m0.022s user 0m0.016s sys 0m0.004s
ocaml xxx.ml: real 0m0.019s user 0m0.015s sys 0m0.003s
ocaml xxx.ml: real 0m0.021s user 0m0.016s sys 0m0.004s
ocaml xxx.ml: real 0m0.020s user 0m0.015s sys 0m0.004s
ocaml xxx.ml: real 0m0.021s user 0m0.016s sys 0m0.004s
ocaml xxx.ml: real 0m0.020s user 0m0.015s sys 0m0.004s
ocaml xxx.ml: real 0m0.021s user 0m0.016s sys 0m0.004s
./xxx: real 0m0.003s user 0m0.001s sys 0m0.002s
./xxx: real 0m0.003s user 0m0.001s sys 0m0.001s
./xxx: real 0m0.003s user 0m0.001s sys 0m0.001s
./xxx: real 0m0.002s user 0m0.001s sys 0m0.001s
./xxx: real 0m0.003s user 0m0.001s sys 0m0.001s
./xxx: real 0m0.005s user 0m0.001s sys 0m0.002s
./xxx: real 0m0.003s user 0m0.001s sys 0m0.002s
./xxx: real 0m0.003s user 0m0.001s sys 0m0.001s
./xxx: real 0m0.003s user 0m0.001s sys 0m0.001s
./xxx: real 0m0.003s user 0m0.001s sys 0m0.001s
./xxx: real 0m0.003s user 0m0.001s sys 0m0.001s
./yyy: real 0m0.002s user 0m0.000s sys 0m0.001s
./yyy: real 0m0.003s user 0m0.000s sys 0m0.001s
./yyy: real 0m0.002s user 0m0.000s sys 0m0.001s
./yyy: real 0m0.002s user 0m0.000s sys 0m0.001s
./yyy: real 0m0.002s user 0m0.000s sys 0m0.001s
./yyy: real 0m0.002s user 0m0.000s sys 0m0.001s
./yyy: real 0m0.002s user 0m0.000s sys 0m0.001s
./yyy: real 0m0.001s user 0m0.000s sys 0m0.001s
./yyy: real 0m0.002s user 0m0.000s sys 0m0.001s
./yyy: real 0m0.002s user 0m0.000s sys 0m0.001s
./yyy: real 0m0.003s user 0m0.000s sys 0m0.002s
./zzz: real 0m0.002s user 0m0.000s sys 0m0.001s
./zzz: real 0m0.002s user 0m0.000s sys 0m0.001s
./zzz: real 0m0.002s user 0m0.000s sys 0m0.001s
./zzz: real 0m0.002s user 0m0.000s sys 0m0.001s
./zzz: real 0m0.002s user 0m0.000s sys 0m0.001s
./zzz: real 0m0.002s user 0m0.000s sys 0m0.001s
./zzz: real 0m0.001s user 0m0.000s sys 0m0.001s
./zzz: real 0m0.002s user 0m0.000s sys 0m0.001s
./zzz: real 0m0.003s user 0m0.000s sys 0m0.002s
./zzz: real 0m0.002s user 0m0.000s sys 0m0.001s
./zzz: real 0m0.002s user 0m0.000s sys 0m0.001s

停止编号：87654

Stop number: 87654

ocaml xxx.ml: real 0m0.102s user 0m0.059s sys 0m0.041s
ocaml xxx.ml: real 0m0.102s user 0m0.059s sys 0m0.040s
ocaml xxx.ml: real 0m0.101s user 0m0.060s sys 0m0.040s
ocaml xxx.ml: real 0m0.103s user 0m0.059s sys 0m0.041s
ocaml xxx.ml: real 0m0.102s user 0m0.059s sys 0m0.041s
ocaml xxx.ml: real 0m0.101s user 0m0.059s sys 0m0.041s
ocaml xxx.ml: real 0m0.102s user 0m0.059s sys 0m0.040s
ocaml xxx.ml: real 0m0.103s user 0m0.059s sys 0m0.040s
ocaml xxx.ml: real 0m0.101s user 0m0.059s sys 0m0.040s
ocaml xxx.ml: real 0m0.102s user 0m0.059s sys 0m0.040s
ocaml xxx.ml: real 0m0.105s user 0m0.059s sys 0m0.041s
./xxx: real 0m0.092s user 0m0.044s sys 0m0.038s
./xxx: real 0m0.087s user 0m0.044s sys 0m0.039s
./xxx: real 0m0.085s user 0m0.044s sys 0m0.038s
./xxx: real 0m0.084s user 0m0.044s sys 0m0.038s
./xxx: real 0m0.085s user 0m0.044s sys 0m0.039s
./xxx: real 0m0.086s user 0m0.045s sys 0m0.039s
./xxx: real 0m0.085s user 0m0.044s sys 0m0.039s
./xxx: real 0m0.085s user 0m0.044s sys 0m0.038s
./xxx: real 0m0.084s user 0m0.044s sys 0m0.038s
./xxx: real 0m0.084s user 0m0.044s sys 0m0.039s
./xxx: real 0m0.083s user 0m0.044s sys 0m0.038s
./yyy: real 0m0.004s user 0m0.003s sys 0m0.001s
./yyy: real 0m0.004s user 0m0.003s sys 0m0.001s
./yyy: real 0m0.004s user 0m0.003s sys 0m0.001s
./yyy: real 0m0.004s user 0m0.003s sys 0m0.001s
./yyy: real 0m0.005s user 0m0.003s sys 0m0.001s
./yyy: real 0m0.005s user 0m0.003s sys 0m0.001s
./yyy: real 0m0.004s user 0m0.003s sys 0m0.001s
./yyy: real 0m0.004s user 0m0.003s sys 0m0.001s
./yyy: real 0m0.004s user 0m0.003s sys 0m0.001s
./yyy: real 0m0.004s user 0m0.003s sys 0m0.001s
./yyy: real 0m0.006s user 0m0.003s sys 0m0.002s
./zzz: real 0m0.004s user 0m0.003s sys 0m0.001s
./zzz: real 0m0.004s user 0m0.003s sys 0m0.001s
./zzz: real 0m0.004s user 0m0.003s sys 0m0.001s
./zzz: real 0m0.004s user 0m0.003s sys 0m0.001s
./zzz: real 0m0.004s user 0m0.003s sys 0m0.001s
./zzz: real 0m0.005s user 0m0.003s sys 0m0.002s
./zzz: real 0m0.004s user 0m0.003s sys 0m0.001s
./zzz: real 0m0.004s user 0m0.003s sys 0m0.001s
./zzz: real 0m0.004s user 0m0.003s sys 0m0.001s
./zzz: real 0m0.004s user 0m0.003s sys 0m0.001s
./zzz: real 0m0.005s user 0m0.003s sys 0m0.001s

显然，因人而异 - 但它似乎OCaml的是由一个相当大的余量比C慢，但是，如果给定的文件中的数字是足够小，则启动和文件读取主导过程时间

Obviously, YMMV - but it appears that OCaml is slower than C by a considerable margin, but that if the number in the given file is small enough, then start up and file reading dominate the process time.

的C时序，特别是在更小的数字，是如此之快，他们是不是所有的可靠。

The C timings, especially at the smaller numbers, are so fast that they are not all that reliable.

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