u-boot/tools/gen_eth_addr.c
Josh Wu 3e4dad5032 tools: gen_eth_addr: add getpid() to time(0) to avoid duplicated seed
As 'time(0) | getpid()' will have a lot of duplicated value. It is not a
expected behavior. We expect different value for the seed when when run
it in many times.

So this patch will left shift the getpid() and add to time(0). That
avoid duplicated value.

Test command is like:
  % RUN=0; while [ $RUN -lt 10000 ]; do
  tools/gen_eth_addr; RUN=$(($RUN+1)); done | sort | uniq | wc -l
  10000

This patch is incorporated with suggestions made by Wolfgang Denk and Andreas
Bießmann. Thanks them a lot.

Signed-off-by: Josh Wu <josh.wu@atmel.com>
Acked-by: Andreas Bießmann <andreas.devel@googlemail.com>
Acked-by: Wolfgang Denk <wd@denx.de>
Tested-by: Wolfgang Denk <wd@denx.de>
2015-09-28 10:48:25 -04:00

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C

/*
* (C) Copyright 2001
* Murray Jensen <Murray.Jensen@cmst.csiro.au>
*
* SPDX-License-Identifier: GPL-2.0+
*/
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <time.h>
int
main(int argc, char *argv[])
{
unsigned long ethaddr_low, ethaddr_high;
srand(time(0) + (getpid() << 8));
/*
* setting the 2nd LSB in the most significant byte of
* the address makes it a locally administered ethernet
* address
*/
ethaddr_high = (rand() & 0xfeff) | 0x0200;
ethaddr_low = rand();
printf("%02lx:%02lx:%02lx:%02lx:%02lx:%02lx\n",
ethaddr_high >> 8, ethaddr_high & 0xff,
ethaddr_low >> 24, (ethaddr_low >> 16) & 0xff,
(ethaddr_low >> 8) & 0xff, ethaddr_low & 0xff);
return (0);
}