Re: [PATCH] iw: add country IE parsing

["Lukáš Turek" <8an@praha12.net>]

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On 18.2.2010 03:13 Luis R. Rodriguez wrote:
> coverage = (distance + 449) / 450;
> coverage/450 = distance + 499
> (coverage/450) - 499 = 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 
coverage class limits maximum distance and if it was rounded down as normal 
integer division does, the resulting ACK timeout would be too low.

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

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

Lukas Turek

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