Re: [Qemu-ppc] [Qemu-devel] [PATCH v2 1/4] target-ppc: Implement bcdcfsq. instruction

[Richard Henderson]

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.


r~