netdev - Re: [PATCH] tcp_probe: avoid modulus operation and wrap fix

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Message-Id: <20100124.224122.13742906.davem@davemloft.net>
Date:	Sun, 24 Jan 2010 22:41:22 -0800 (PST)
From:	David Miller <davem@...emloft.net>
To:	shemminger@...tta.com
Cc:	netdev@...r.kernel.org
Subject: Re: [PATCH] tcp_probe: avoid modulus operation and wrap fix

From: Stephen Hemminger <shemminger@...tta.com>
Date: Sun, 24 Jan 2010 21:50:01 -0800

> @@ -75,12 +75,12 @@ static struct {
>  
>  static inline int tcp_probe_used(void)
>  {
> -	return (tcp_probe.head - tcp_probe.tail) % bufsize;
> +	return (tcp_probe.head - tcp_probe.tail) & (bufsize - 1);
>  }
>  
>  static inline int tcp_probe_avail(void)
>  {
> -	return bufsize - tcp_probe_used();
> +	return bufsize - tcp_probe_used() - 1;
>  }
>  
>  /*

Hmmm...  When the ring is full head==tail, which means
tcp_probe_used() returns 0.  Which would now make tcp_probe_avail()
return "bufsize - 0 - 1".

Is that right?
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