Re: [RFC PATCH] target/i386: for maximum rounding precision for fildll

[Richard Henderson]

On 3/7/22 08:44, Alex Bennée wrote:
> The instruction description says "It is loaded without rounding
> errors." which implies we should have the widest rounding mode
> possible.
>
> Resolves: https://gitlab.com/qemu-project/qemu/-/issues/888
> Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
> ---
>   target/i386/tcg/fpu_helper.c | 4 ++++
>   1 file changed, 4 insertions(+)
>
> diff --git a/target/i386/tcg/fpu_helper.c b/target/i386/tcg/fpu_helper.c
> index cdd8e9f947..d986fd5792 100644
> --- a/target/i386/tcg/fpu_helper.c
> +++ b/target/i386/tcg/fpu_helper.c
> @@ -250,11 +250,15 @@ void helper_fildl_ST0(CPUX86State *env, int32_t val)
>   void helper_fildll_ST0(CPUX86State *env, int64_t val)
>   {
>       int new_fpstt;
> +    FloatX80RoundPrec old = get_floatx80_rounding_precision(&env->fp_status);
> +    set_floatx80_rounding_precision(floatx80_precision_x, &env->fp_status);
>   
>       new_fpstt = (env->fpstt - 1) & 7;
>       env->fpregs[new_fpstt].d = int64_to_floatx80(val, &env->fp_status);
>       env->fpstt = new_fpstt;
>       env->fptags[new_fpstt] = 0; /* validate stack entry */
> +
> +    set_floatx80_rounding_precision(old, &env->fp_status);
>   }

Yep.

Need a similar fix for fildl_ST0, for the case floatx80_precision_s is currently set 
(int32_t has more than the 23 bits of single-precision).


r~