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Re: Fwd: about udelay in mips

To: Ian Lance Taylor <iant@google.com>
Subject: Re: Fwd: about udelay in mips
From: "Maciej W. Rozycki" <macro@linux-mips.org>
Date: Thu, 27 Jan 2011 21:42:50 +0000 (GMT)
Cc: loody <miloody@gmail.com>, Sergei Shtylyov <sshtylyov@mvista.com>, gcc-help <gcc-help@gcc.gnu.org>, Linux MIPS Mailing List <linux-mips@linux-mips.org>
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On Thu, 27 Jan 2011, Ian Lance Taylor wrote:

> I don't know the type of HZ.  But assuming it is a constant, then the
> rules of C are that the expression
>     us * 0x000010c7 * HZ * lpj
> gets evaluated in the type "unsigned long".  The fact that you then cast
> that "unsigned long" value to "unsigned long long" does not cause the
> multiplication to be done in the type "unsigned long long".
> 
> You need to write something like
>     (unsigned long long) us * 0x000010c7 * HZ * (unsigned long long) lpj
> to get the multiplication to be done in the "unsigned long long" type.

 Though as a matter of coding style, personally I'd rather assigned "us" 
to a local variable of the "unsigned long long" type and performed all the 
calculations on it instead, avoiding any explicit casts and doubts as to 
what type is being used altogether.

  Maciej

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