On Sun, Jun 24, 2018 at 10:53:37PM -0400, Steve Litt wrote:
> On Thu, 21 Jun 2018 00:56:04 +0200
> Tomasz Rola <rto...@ceti.pl> wrote:
>
[...]
> > Craps. I have consulted OpenBSD's manpage for dd and there is no
> > mention of iflag. So this will not work on OpenBSD. I will have to
> > rethink this, sorry.
> >
>
> Untested...
>
> int main(int argc, char* argv[]){
> long l = atod(argv[1]);
> while(l--){
> if (c = getc(STDIN) != EOF)
> putc(c, STDOUT);
> else
> break;
> }
> return 0;
> }
>
> I haven't tested it so it might not be exactly right, and of course
> error handling would need to be added, but you know what I mean. IIRC
> getc() and putc() are very well buffered so it will be fast. In my
> youth I wrote similar functions using low level read() and write() and
> doing my own buffering, and those things were *really* fast, but I
> think that's overkill in this century.
>
> As far as finding command line tools that do it, if that's becoming
> hard to do, why not just write a 10 line program?
Actually, I have written few such programs to satiate my own curiosity
- I was dragged away from computer and in the meantime, others joined
thread and even wrote nice buffered version of solution in C. I pitted
this solution against my programs (in C, with fgetc/fputc and Common
Lisp, with read-sequence/write-sequence) and head-c.c was many times
faster (about hundred or more times) than my programs.
I am not sure if there is performance difference between fgetc/fputc
and getc/putc. Man says getc are macros around fgetc. Might be worth
checking, but I guess no difference.
My curiosity also "wanted" to know how much of performance hit was to
be expected when writing best to my knowledge optimised Common Lisp vs
simplistic C - they were similar in performance, with CL compiled by
SBCL and few times slower, and head-c.c had beaten them both by many
lengths. I am a bit surprised that in CL, performance was about the
same, whether reading one byte or many at once. Perhaps I will find a
way to speed it up some more.
As of finding command line tools, I had working script in about an
hour (and buggy one in few minutes). Buggy, because "dd | dd" is bad
idea, and after finding better options for using dd in my script -
which worked, but under Linux - I had also found out they would not
work in OpenBSD.
So, I consider it a worthy lesson for myself. Next time, I might just
fire up Emacs and write a script in CL (mostly, because this is what
is comfy for me nowadays, and I will not object against having compiled
script for free). Or something similar, or maybe even do it in C, why
not.
BTW, the version of nread.sh (improved options) was on par with
head-c.c, so writing a script with right things inside is very good
choice, too. If the script actually works :-) .
While the speed is not big problem for input of about 1 megabyte, it
becomes a problem when gigabytes are copied.
--
Regards,
Tomasz Rola
--
** A C programmer asked whether computer had Buddha's nature. **
** As the answer, master did "rm -rif" on the programmer's home **
** directory. And then the C programmer became enlightened... **
** **
** Tomasz Rola mailto:tomasz_r...@bigfoot.com **
