From: Michael J Gruber <git@drmicha.warpmail.net>
Date: Wed, 20 Apr 2011 11:00:07 GMT
Subject: Re: [PATCH] date: avoid "X years, 12 months" in relative dates
Message-ID: <4DAEBCB7.80707@drmicha.warpmail.net>
In-Reply-To: <20110420101800.GA24035@sigill.intra.peff.net>

Jeff King venit, vidit, dixit 20.04.2011 12:18:
> On Wed, Apr 20, 2011 at 11:12:11AM +0200, Michael J Gruber wrote:
> 
>> Implement this differently with months of size
>>
>>   onemonth = 365/12
>>
>> so that
>>
>>   totalmonths = (long)( (days + onemonth/2)/onemonth )
>>   years = totalmonths / 12
>>   months = totalmonths % 12
>>
>> In order to do this without floats, we write the first formula as
>>
>>   totalmonths = (days*12*2 + 365) / (365*2)
> 
> Well now I feel like an idiot. Algebra to the rescue.

:)

> The extra multiplications introduce the possibility of overflow, but
> since the number of days was arrived at by dividing an unsigned long
> number of seconds by 86400, we are guaranteed to have room to multiply
> by 24. :)

Also, this is inside "if (diff < 1825)", so no matter where diff comes
from, "long" is really long enough.

Cheers,
Michael