Hello,
On Mon, 15 Jun 2020, Dale wrote:
[..]
>While I'm at it, when running dd, I have zero and random in /dev. Where
>does a person obtain a one? In other words, I can write all zeros, I
>can write all random but I can't write all ones since it isn't in /dev.
>Does that even exist? Can I create it myself somehow? Can I download
>it or install it somehow? I been curious about that for a good long
>while now. I just never remember to ask.
I've wondered that too. So I just hacked one up just now.
==== ones.c ====
#include <unistd.h>
#include <stdlib.h>
#include <stdio.h>
static unsigned int buf[BUFSIZ];
int main(void) {
unsigned int i;
for(i = 0; i < BUFSIZ; i++) { buf[i] = (unsigned int)-1; }
while( write(STDOUT_FILENO, buf, sizeof(buf)) );
exit(0);
}
====
Compile with:
gcc $CFLAGS -o ones ones.c
or
gcc $(portageq envvar CFLAGS) -o ones ones.c
and use/test e.g. like
./ones | dd of=/dev/null bs=8M count=1000 iflag=fullblock
Here, it's about as fast as
cat /dev/zero | dd of=/dev/null bs=8M count=1000 iflag=fullblock
(but only about ~25% as fast as
dd if=/dev/zero of=/dev/null bs=8M count=1000 iflag=fullblock
for whatever reason ever, but the implementation of /dev/zero is
non-trivial ...)
HTH,
-dnh
--
Computers make very fast, very accurate mistakes.
