Re: Slowness in function 'open'

[Dmitri A. Sergatskov]

Another option. You can pipe your file through text to binary
converter written in C like e.g.[1]:


/* begin */
#include <stdio.h>

int
main(void)
{
       double a;
       while(EOF != fscanf(stdin, "%lf", &a)){
               fwrite(&a, sizeof(double), 1, stdout);
       }
       return 0;
}
/* end */

gcc -Wall -O2 readit.c -o readit

time ./readit < xxx.dat > zzz.bin


real    0m1.702s
user    0m1.624s
sys     0m0.076s

And than in octave (since the file is not in octave format,
you still need to do a low-level file i/o)

octave:6> fh=fopen("zzz.bin");
octave:7> tic; [a, count] = fread(fh, inf, 'double'); toc
Elapsed time is 0.780479 seconds.
octave:8> count/5
ans =  512000

This is 1.7 + 0.78 ~2.5 sec total time which  is ~2.5 times faster
on my computer than reading the original ASCII file (6.6 sec).

Sincerely,

Dmitri.
p.s. [1] perhaps, the program can be improved by doing some buffering
on i/o, but I am too lazy to do it myself :)
--