netdev - Re: [PATCH] udp: port starting location not random

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Message-ID: <0a842600-9707-4465-a5ea-6acfb38a9a70@tahiti.vyatta.com>
Date:	Thu, 04 Oct 2012 15:06:34 -0700 (PDT)
From:	Stephen Hemminger <stephen.hemminger@...tta.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	netdev@...r.kernel.org, David Miller <davem@...emloft.net>
Subject: Re: [PATCH] udp: port starting location not random

Nevermind, it depends on random being big enough. This shows that it
works with large enough random(). The hash I was getting from VXLAN
was too small...

#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>

int main(int ac, char **av) {
	int low, high, remaining;
	unsigned int rand;
	unsigned short first;
	
	low = atoi(av[1]);
	high = atoi(av[2]);
	remaining = (high - low) + 1;
	srandom(getpid());
	rand = (uint32_t) random();
	
	first = (((uint64_t)rand * remaining) >> 32) + low;

	printf("%d %d %u => %u\n", low, high, rand, first);
	return 0;
}
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