[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: [Qemu-devel] [PATCH v2 1/4] target-ppc: Implement bcdcfsq. instructi
From: |
David Gibson |
Subject: |
Re: [Qemu-devel] [PATCH v2 1/4] target-ppc: Implement bcdcfsq. instruction |
Date: |
Thu, 24 Nov 2016 12:20:35 +1100 |
User-agent: |
Mutt/1.7.1 (2016-10-04) |
On Thu, Nov 24, 2016 at 01:43:18AM +0100, Richard Henderson wrote:
> On 11/23/2016 05:21 PM, Jose Ricardo Ziviani wrote:
> > bcdcfsq.: Decimal convert from signed quadword. It is not possible
> > to convert values less than 10^31-1 or greater than -10^31-1 to be
> > represented in packed decimal format.
> >
> > Signed-off-by: Jose Ricardo Ziviani <address@hidden>
> > ---
> > target-ppc/helper.h | 1 +
> > target-ppc/int_helper.c | 45
> > +++++++++++++++++++++++++++++++++++++
> > target-ppc/translate/vmx-impl.inc.c | 7 ++++++
> > 3 files changed, 53 insertions(+)
> >
> > diff --git a/target-ppc/helper.h b/target-ppc/helper.h
> > index da00f0a..87f533c 100644
> > --- a/target-ppc/helper.h
> > +++ b/target-ppc/helper.h
> > @@ -382,6 +382,7 @@ DEF_HELPER_3(bcdcfn, i32, avr, avr, i32)
> > DEF_HELPER_3(bcdctn, i32, avr, avr, i32)
> > DEF_HELPER_3(bcdcfz, i32, avr, avr, i32)
> > DEF_HELPER_3(bcdctz, i32, avr, avr, i32)
> > +DEF_HELPER_3(bcdcfsq, i32, avr, avr, i32)
> >
> > DEF_HELPER_2(xsadddp, void, env, i32)
> > DEF_HELPER_2(xssubdp, void, env, i32)
> > diff --git a/target-ppc/int_helper.c b/target-ppc/int_helper.c
> > index 8886a72..751909c 100644
> > --- a/target-ppc/int_helper.c
> > +++ b/target-ppc/int_helper.c
> > @@ -2874,6 +2874,51 @@ uint32_t helper_bcdctz(ppc_avr_t *r, ppc_avr_t *b,
> > uint32_t ps)
> > return cr;
> > }
> >
> > +uint32_t helper_bcdcfsq(ppc_avr_t *r, ppc_avr_t *b, uint32_t ps)
> > +{
> > + int cr;
> > + int i;
> > + int ox_flag = 0;
> > + uint64_t lo_value;
> > + uint64_t hi_value;
> > + uint64_t max = 0x38d7ea4c68000;
>
> This is at heart a decimal number, and should be written as such.
> Also, you need ULL for a 32-bit host compile.
>
> > + if (divu128(&lo_value, &hi_value, max)) {
> > + ox_flag = 1;
> > + } else if (lo_value >= max && hi_value == 0) {
> > + ox_flag = 1;
> > + }
>
> Dispense with ox_flag and set cr = CRF_SO now.
>
> > + for (i = 1; hi_value; hi_value /= 10, i++) {
> > + bcd_put_digit(&ret, hi_value % 10, i);
> > + }
> > +
> > + for (; lo_value; lo_value /= 10, i++) {
> > + bcd_put_digit(&ret, lo_value % 10, i);
> > + }
>
> How can this possibly work? You know there are 15 digits between high and
> low, but you continue with i++?
>
> If hi_value == 1 && lo_value == 1, this should not produce 11, but
> 10000000000000001.
Ah, yes good catch, I missed that. I think it will be clearer to use
fixed bounds on each loop, rather than testing the value of the
remaining result.
--
David Gibson | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_
| _way_ _around_!
http://www.ozlabs.org/~dgibson
signature.asc
Description: PGP signature