Re: [Qemu-devel] [PATCH] target/ppc: Set float_tininess_before_rounding at cpu reset

[Paul Clarke]

On 8/26/19 9:00 PM, Richard Henderson wrote:
> As defined in Power 3.0 section 4.4.4 "Underflow Exception",
> a tiny result is detected before rounding.

Responded in the bug:
https://bugs.launchpad.net/qemu/+bug/1841491/comments/3

In my testing, this works for "double", but not "float".

> Fixes: https://bugs.launchpad.net/qemu/+bug/1841491 
> Reported-by: Paul Clarke <address@hidden>
> Signed-off-by: Richard Henderson <address@hidden>
> ---
>  target/ppc/translate_init.inc.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/target/ppc/translate_init.inc.c b/target/ppc/translate_init.inc.c
> index 4a21ed7289..023138c2f9 100644
> --- a/target/ppc/translate_init.inc.c
> +++ b/target/ppc/translate_init.inc.c
> @@ -10461,6 +10461,10 @@ static void ppc_cpu_reset(CPUState *s)
>      s->exception_index = POWERPC_EXCP_NONE;
>      env->error_code = 0;
>  
> +    /* tininess for underflow is detected before rounding */
> +    set_float_detect_tininess(float_tininess_before_rounding,
> +                              &env->fp_status);
> +
>      for (i = 0; i < ARRAY_SIZE(env->spr_cb); i++) {
>          ppc_spr_t *spr = &env->spr_cb[i];

PC