Re: [OpenBIOS] [PATCH 10/10] Adding filll Forth primitive

[Segher Boessenkool]

> +static void filll(void)
> +{
> ucell value = POP();
> ucell count = POP();
> ucell *dest = (ucell *)cell2pointer(POP());
> int i;
> for (i = 0; i <= count / 4; i++) {
>    dest[i] = value;
> }
>
> +}

Apple's code does:

int *dest ... ;
for (i = count; i > 0; i -= 4)
    *dest++ = value;

which is not the same thing for huge count, or for count a multiple
of four (like all callers I have seen use; you write a word too many).

Segher

[PATCH 10/10] Adding filll Forth primitive

[Segher Boessenkool]

> Apple's code does:
>
> int *dest ... ;
> for (i = count; i > 0; i -= 4)
>    *dest++ = value;

Oh, and it does an unsigned 32-bit read for the (signed) count;
this means that on 64-bit systems it does not work for negative
count values.  Not that it is ever called like that, heh.

Here's the code if you care (from 5.2.4f1, i.e. for G5 machines):

58c0:       7e 84 a3 78     mr      r4,r20
     58c4:       80 7f 00 00     lwz     r3,0(r31)
     58c8:       80 bf 00 04     lwz     r5,4(r31)
     58cc:       7c 63 1b 79     mr.     r3,r3
     58d0:       86 9f 00 08     lwzu    r20,8(r31)
     58d4:       3b ff 00 04     addi    r31,r31,4
     58d8:       40 81 00 14     ble     0x58ec
     58dc:       34 63 ff fc     addic.  r3,r3,-4
     58e0:       90 85 00 00     stw     r4,0(r5)
     58e4:       38 a5 00 04     addi    r5,r5,4
     58e8:       42 80 ff f0     bc      20,lt,0x58d8
     58ec:       4e 80 00 20     blr

Segher

[PATCH 10/10] Adding filll Forth primitive

[Mark Cave-Ayland]

On 17/08/11 09:03, Segher Boessenkool wrote:
> > Apple's code does:
> >
> > int *dest ... ;
> > for (i = count; i > 0; i -= 4)
> > *dest++ = value;
>
> Oh, and it does an unsigned 32-bit read for the (signed) count;
> this means that on 64-bit systems it does not work for negative
> count values. Not that it is ever called like that, heh.
>
> Here's the code if you care (from 5.2.4f1, i.e. for G5 machines):
>
> 58c0: 7e 84 a3 78 mr r4,r20
> 58c4: 80 7f 00 00 lwz r3,0(r31)
> 58c8: 80 bf 00 04 lwz r5,4(r31)
> 58cc: 7c 63 1b 79 mr. r3,r3
> 58d0: 86 9f 00 08 lwzu r20,8(r31)
> 58d4: 3b ff 00 04 addi r31,r31,4
> 58d8: 40 81 00 14 ble 0x58ec
> 58dc: 34 63 ff fc addic. r3,r3,-4
> 58e0: 90 85 00 00 stw r4,0(r5)
> 58e4: 38 a5 00 04 addi r5,r5,4
> 58e8: 42 80 ff f0 bc 20,lt,0x58d8
> 58ec: 4e 80 00 20 blr
>
> Segher

Interesting. In that case William, rather than add it directly to the 
list of primitive words, can you add it into arch/ppc/qemu/init.c and 
then call bind_func() instead? (see bottom of the same file for an 
example). This will then keep it as PPC-specific.

ATB,

Mark.