Re: loader: Build the preloader for ARM

[Alexandre Julliard]

André Hentschel  writes:
> +unsigned int wld_modulo( const unsigned int a, const Elf32_Word b )
> +{
> +#ifdef __ARM_EABI__
> - unsigned int i;
> - if(b > a) return a;
> - for(i = 0; i * b < a + b; i++)
> -
>    if(i * b > a - b) return (a - i * b);
> - return 0;

That's very inefficient, there are better ways...

loader: Build the preloader for ARM

[André Hentschel]

Am 04.02.2011 16:31, schrieb Alexandre Julliard:
> André Hentschel  writes:
> > +unsigned int wld_modulo( const unsigned int a, const Elf32_Word b )
> > +{
> > +#ifdef __ARM_EABI__
> > - unsigned int i;
> > - if(b > a) return a;
> > - for(i = 0; i * b < a + b; i++)
> > -
> >    if(i * b > a - b) return (a - i * b);
> > - return 0;
>
> That's very inefficient, there are better ways...

Thanks for having a look at it.
The Problem is that i also can't use '/', otherwise it wants to link to __aeabi_uidiv .
That leads to some Problems, so i'll try to find some better math solution and if that fails i maybe try it the assembler way...

loader: Build the preloader for ARM

[Marcus Meissner]

On Fri, Feb 04, 2011 at 04:51:46PM +0100, André Hentschel wrote:
> Am 04.02.2011 16:31, schrieb Alexandre Julliard:
> > André Hentschel  writes:
> > > +unsigned int wld_modulo( const unsigned int a, const Elf32_Word b )
> > > +{
> > > +#ifdef __ARM_EABI__
> > > - unsigned int i;
> > > - if(b > a) return a;
> > > - for(i = 0; i * b < a + b; i++)
> > > -
> > >    if(i * b > a - b) return (a - i * b);
> > > - return 0;
> >
> > That's very inefficient, there are better ways...
>
> Thanks for having a look at it.
> The Problem is that i also can't use '/', otherwise it wants to link to __aeabi_uidiv .
> That leads to some Problems, so i'll try to find some better math solution and if that fails i maybe try it the assembler way...

modulo would be "%" btw,

return a%b;

but this might generate external functions too... hmm, try -Os as option?

Ciao, Marcus

loader: Build the preloader for ARM

[André Hentschel]

Am 04.02.2011 17:26, schrieb Marcus Meissner:
> On Fri, Feb 04, 2011 at 04:51:46PM +0100, André Hentschel wrote:
> > Am 04.02.2011 16:31, schrieb Alexandre Julliard:
> > > André Hentschel  writes:
> > > > +unsigned int wld_modulo( const unsigned int a, const Elf32_Word b )
> > > > +{
> > > > +#ifdef __ARM_EABI__
> > > > - unsigned int i;
> > > > - if(b > a) return a;
> > > > - for(i = 0; i * b < a + b; i++)
> > > > -
> > > >    if(i * b > a - b) return (a - i * b);
> > > > - return 0;
> > >
> > > That's very inefficient, there are better ways...
> >
> > Thanks for having a look at it.
> > The Problem is that i also can't use '/', otherwise it wants to link to __aeabi_uidiv .
> > That leads to some Problems, so i'll try to find some better math solution and if that fails i maybe try it the assembler way...
>
> modulo would be "%" btw,
>
> return a%b;
>
> but this might generate external functions too... hmm, try -Os as option?
>
> Ciao, Marcus

% and / both lead to external dependencies here...
maybe the euclidean algorithm helps, because -Os would need ugly changes to configure i guess.

loader: Build the preloader for ARM

[Peter Rosin]

Den 2011-02-04 17:41 skrev André Hentschel:
> Am 04.02.2011 17:26, schrieb Marcus Meissner:
> > On Fri, Feb 04, 2011 at 04:51:46PM +0100, André Hentschel wrote:
> > > Am 04.02.2011 16:31, schrieb Alexandre Julliard:
> > > > André Hentschel  writes:
> > > > > +unsigned int wld_modulo( const unsigned int a, const Elf32_Word b )
> > > > > +{
> > > > > +#ifdef __ARM_EABI__
> > > > > - unsigned int i;
> > > > > - if(b > a) return a;
> > > > > - for(i = 0; i * b < a + b; i++)
> > > > > -
> > > > >    if(i * b > a - b) return (a - i * b);
> > > > > - return 0;
> > > >
> > > > That's very inefficient, there are better ways...
> > >
> > > Thanks for having a look at it.
> > > The Problem is that i also can't use '/', otherwise it wants to link to __aeabi_uidiv .
> > > That leads to some Problems, so i'll try to find some better math solution and if that fails i maybe try it the assembler way...
> >
> > modulo would be "%" btw,
> >
> > return a%b;
> >
> > but this might generate external functions too... hmm, try -Os as option?
> >
> > Ciao, Marcus
>
> % and / both lead to external dependencies here...
> maybe the euclidean algorithm helps, because -Os would need ugly changes to configure i guess.

Finding gcd is a bit over the top...

How about something like the following?

Cheers,
Peter

unsigned int wld_modulo( const unsigned int a, const Elf32_Word b )
{
#ifdef __ARM_EABI__
    unsigned int r = 0;
    int i;

for (i = sizeof(a) * 8 - 1; i >= 0; --i) {
    	r <<= 1;
    	if (a & (1U << i))
    		r |= 1;
    	if (r > b)
    		r -= b;
    }

return r;
...

loader: Build the preloader for ARM

[Peter Rosin]

Den 2011-02-04 20:36 skrev Peter Rosin:
> Den 2011-02-04 17:41 skrev André Hentschel:
> > % and / both lead to external dependencies here...
> > maybe the euclidean algorithm helps, because -Os would need ugly changes to configure i guess.
>
> Finding gcd is a bit over the top...
>
> How about something like the following?
>
> Cheers,
> Peter
>
> unsigned int wld_modulo( const unsigned int a, const Elf32_Word b )
> {
> #ifdef __ARM_EABI__
>    unsigned int r = 0;
>    int i;
>
> for (i = sizeof(a) * 8 - 1; i >= 0; --i) {
>    	r <<= 1;
>    	if (a & (1U << i))
>    		r |= 1;
>    	if (r > b)

Ooops, bug. Should be "if (r >= b)"
> 	r -= b;
>
> }
>
> return r;
> ...

Cheers,
Peter