Date: Fri, 8 Oct 2004 20:56:39 -0500 From: Dan Nelson <dnelson@allantgroup.com> To: "Li, Qing" <qing.li@bluecoat.com> Cc: freebsd-hackers@freebsd.org Subject: Re: Bit field definition ? Message-ID: <20041009015639.GB3106@dan.emsphone.com> In-Reply-To: <00CDF9AA240E204FA6E923BD35BC643606BF68E3@bcs-mail.internal.cacheflow.com> References: <00CDF9AA240E204FA6E923BD35BC643606BF68E3@bcs-mail.internal.cacheflow.com>
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In the last episode (Oct 08), Li, Qing said:
> The bit fields "th_x2" and "th_off" in "struct tcphdr",
> even though defined as "u_int", actually occupies 1 byte.
u_int th_x2:4, /* (unused) */
th_off:4; /* data offset */
The :4 after each variable means 4 bits long, so both fields together
take up 8 bits = 1 byte. That's the whole purpose of bitfields :)
--
Dan Nelson
dnelson@allantgroup.com
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