From: =?utf-8?q?Luk=C3=A1=C5=A1_Turek?= <8an@praha12.net>
Reply-To: 8an@praha12.net
To: "Luis R. Rodriguez" <lrodriguez@atheros.com>
Subject: Re: [PATCH] iw: add country IE parsing
Date: Thu, 18 Feb 2010 22:40:31 +0100
Cc: johannes@sipsolutions.net, linux-wireless@vger.kernel.org
References: <1266459208-12408-1-git-send-email-lrodriguez@atheros.com>
In-Reply-To: <1266459208-12408-1-git-send-email-lrodriguez@atheros.com>
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On 18.2.2010 03:13 Luis R. Rodriguez wrote:
> coverage =3D (distance + 449) / 450;
> coverage/450 =3D distance + 499
> (coverage/450) - 499 =3D distance

Inverting the formula like this doesn't make much sense...

The addition of 449 is there to round the resulting number up, because the=
=20
coverage class limits maximum distance and if it was rounded down as normal=
=20
integer division does, the resulting ACK timeout would be too low.

However, if you subtract 449 in the inverted formula, you get something lik=
e a=20
minimum distance for the coverage class - which doesn't mean anything,=20
because higher ACK timeout and slot time works for smaller distances too.=20
Maximum distance is what's interesting to the user. So the correct=20
calculation is just multiplying the coverage class by 450 as I'm doing in=20
print_phy_handler():

printf("\tCoverage class: %d (up to %dm)\n", coverage, 450 * coverage);

Lukas Turek

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