Re: [PATCH] Add udivmoddi4.

[Tom Rini <trini@konsulko.com>]

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On Wed, Jun 09, 2021 at 09:20:20PM +0200, Christian Melki wrote:
> On 6/9/21 8:31 PM, Tom Rini wrote:
> > On Mon, Jun 07, 2021 at 11:20:47AM +0200, Christian Melki wrote:
> > 
> >> A newer toolchain will emit udivmoddi4 for certain divide + modulo
> >> operations instead of a separate divide and modulo operation.
> >> AFAIU, this would be sufficient.
> >>
> >> Signed-off-by: Christian Melki <christian.melki@t2data.com>
> >> ---
> >>  arch/x86/lib/div64.c | 5 +++++
> >>  1 file changed, 5 insertions(+)
> >>
> >> diff --git a/arch/x86/lib/div64.c b/arch/x86/lib/div64.c
> >> index 2bea205f60..a5b536fbc5 100644
> >> --- a/arch/x86/lib/div64.c
> >> +++ b/arch/x86/lib/div64.c
> >> @@ -110,3 +110,8 @@ u64 __umoddi3(u64 num, u64 den)
> >>  	_64bit_divide(num, den, &v);
> >>  	return v;
> >>  }
> >> +
> >> +u64 __udivmoddi4(u64 num, u64 den, u64 *rem)
> >> +{
> >> +	return _64bit_divide(num, den, rem);
> >> +}
> > 
> > How do you trigger this and should you not be using do_div(), etc,
> > instead?
> > 
> 
> I probably should. Was trying to minimize various dependencies on u-boot
> code (atleast with function separation) while trying to implement a
> redundancy boot mechanism as a cmd. Triggered by using two consecutive
> calls between the same variables for division and remainder as pure
> operands with a gcc 9.3 x86 toolchain.
> 
> U-boot has no div_up afaik?
> 
> a = b / c;
> if (b % c) {
>     a++;
> }
> 
> b / c and b % c gets optimized / translated to udivmoddi4 as one operation.

I think you should look at include/div64.h and see if what you want is
handled by something there already.

-- 
Tom

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