From: Ilmari Heikkinen <ilmari.heikkinen@...>
Date: 2007-09-25T08:50:33+09:00
Subject: Re: I am new to Ruby and I could use some expert advice as to how I can make this code run faster.

On 9/24/07, Ilmari Heikkinen <ilmari.heikkinen@gmail.com> wrote:
> On 9/24/07, Joel VanderWerf <vjoel@path.berkeley.edu> wrote:
> > On 9/24/07, Ilmari Heikkinen <ilmari.heikkinen@gmail.com> wrote:
> > ...
> >  > And here's a C version:
> >
> > To give C its fair due, you might try with
> >
> >     unsigned long *buf;
> >
> > and
> >
> >         buf[i] |= 0x80808080;
> >
> > (and the other necessary changes, of course).
> >

> And a version with 64-bit ints was even faster. But it had a bug too.
>
> Anyone wish to contribute working versions :)?

Guess not, so here's one:

$ time ./scramble64 trace trace.scramblec

real	0m0.022s
user	0m0.004s
sys	0m0.020s

$ export RUBYOPT=  # -rubygems takes ~40ms
$ time ruby -rscramble -e 'scramble_nobu("trace")'

real	0m0.049s
user	0m0.016s
sys	0m0.032s

$ diff trace.scramble*
$

$ cat scramble64.c

#include <stdlib.h>
#include <stdio.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <unistd.h>

#define BUF_SIZE 4096

int main(int argc, char** argv) {
 int i, j, k, rsz, wsz;
 FILE *in_f, *out_f;
 unsigned long long isz;
 struct stat st;
 long long buf[BUF_SIZE];

 if (argc != 3) {
   printf("USAGE: %s INFILE OUTFILE\n", argv[0]);
   return 1;
 }

 isz = sizeof(long long);

 in_f = fopen(argv[1], "r");
 if (NULL == in_f) {
   printf("Failed to open input file %s\n", argv[0]);
   return 2;
 }

 out_f = fopen(argv[2], "w");
 if (NULL == out_f) {
   printf("Failed to open output file %s\n", argv[1]);
   fclose(in_f);
   return 4;
 }

 fstat(fileno(in_f), &st);
 for(i=0,j = st.st_size / (isz*BUF_SIZE); i<j; i++) {
   rsz = fread(buf, isz, BUF_SIZE, in_f);
   for(k=0; k<rsz; k++)
     buf[k] |= 0x8080808080808080;
   wsz = fwrite(buf, isz, rsz, out_f);
   if (wsz != rsz) {
     printf("Failed to write to output file\n");
     break;
   }
 }
 rsz = fread(buf, 1, isz*BUF_SIZE, in_f);
 for(k=0; k<rsz; k++)
   ((char*)buf)[k] |= 0x80;
 wsz = fwrite(buf, 1, rsz, out_f);
 if (wsz != rsz) {
   printf("Failed to write to output file\n");
 }

 fclose(in_f);
 fclose(out_f);
 return 0;
}