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From: Segher Boessenkool <segher@kernel.crashing.org>
Subject: Re: V4L2: __ucmpdi2 undefined on ppc
Date: Tue, 4 Mar 2008 23:43:25 +0100
To: Paul Mackerras <paulus@samba.org>
Cc: linuxppc-dev@ozlabs.org, henrik.sorensen@gmail.com,
	Stephane Marchesin <marchesin@icps.u-strasbg.fr>,
	David Woodhouse <dwmw2@infradead.org>
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>> Every occurrence of r7 here is wrong (and some of the r6).  Is there
>> any reason to do this in assembler code at all?
>
> The fact that the obvious C code generates ... a call to __ucmpdi2? :)

Hrm?  Here's the "obvious" C code, portable to all architectures
(modulo the specific types used, this isn't a proposed patch):


unsigned int ucmpdi2(unsigned long long a, unsigned long long b)
{
         unsigned long ahi, bhi, alo, blo;

         ahi = a >> 32;
         bhi = b >> 32;
         if (ahi < bhi)
                 return 0;
         if (ahi > bhi)
                 return 2;

         alo = a;
         blo = b;
         if (alo < blo)
                 return 0;
         if (alo > blo)
                 return 2;

         return 1;
}


(libgcc does it a bit differently, with unions and stuff).


Segher