Re: [PATCH 6/7] target/i386: reimplement fprem1 using floatx80 operations

[Alex Bennée]

Joseph Myers <joseph@codesourcery.com> writes:

> The x87 fprem1 emulation is currently based around conversion to
> double, which is inherently unsuitable for a good emulation of any
> floatx80 operation.  Reimplement using the soft-float floatx80
> remainder operations.
>
> Signed-off-by: Joseph Myers <joseph@codesourcery.com>
> ---
>  target/i386/fpu_helper.c | 96 +++++++++++++++++++---------------------
>  1 file changed, 45 insertions(+), 51 deletions(-)
>
> diff --git a/target/i386/fpu_helper.c b/target/i386/fpu_helper.c
> index 8ef5b463ea..bab35e00a0 100644
> --- a/target/i386/fpu_helper.c
> +++ b/target/i386/fpu_helper.c
> @@ -934,63 +934,57 @@ void helper_fxtract(CPUX86State *env)
>      merge_exception_flags(env, old_flags);
>  }
>  
> -void helper_fprem1(CPUX86State *env)
> +static void helper_fprem_common(CPUX86State *env, bool mod)
>  {
> -    double st0, st1, dblq, fpsrcop, fptemp;
> -    CPU_LDoubleU fpsrcop1, fptemp1;
> -    int expdif;
> -    signed long long int q;
> -
> -    st0 = floatx80_to_double(env, ST0);
> -    st1 = floatx80_to_double(env, ST1);
> -
> -    if (isinf(st0) || isnan(st0) || isnan(st1) || (st1 == 0.0)) {
> -        ST0 = double_to_floatx80(env, 0.0 / 0.0); /* NaN */
> -        env->fpus &= ~0x4700; /* (C3,C2,C1,C0) <-- 0000 */
> -        return;
> -    }
> -
> -    fpsrcop = st0;
> -    fptemp = st1;
> -    fpsrcop1.d = ST0;
> -    fptemp1.d = ST1;
> -    expdif = EXPD(fpsrcop1) - EXPD(fptemp1);
> -
> -    if (expdif < 0) {
> -        /* optimisation? taken from the AMD docs */
> -        env->fpus &= ~0x4700; /* (C3,C2,C1,C0) <-- 0000 */
> -        /* ST0 is unchanged */
> -        return;
> -    }
> +    uint8_t old_flags = save_exception_flags(env);

Hmm where did this come from:

/home/alex/lsrc/qemu.git/target/i386/fpu_helper.c: In function 
‘helper_fprem_common’:
/home/alex/lsrc/qemu.git/target/i386/fpu_helper.c:784:25: error: implicit 
declaration of function ‘save_exception_flags’; did you mean 
‘raise_exception_ra’? [-Werror=implicit-function-declaration]
     uint8_t old_flags = save_exception_flags(env);
                         ^~~~~~~~~~~~~~~~~~~~
                         raise_exception_ra
/home/alex/lsrc/qemu.git/target/i386/fpu_helper.c:784:25: error: nested extern 
declaration of ‘save_exception_flags’ [-Werror=nested-externs]
/home/alex/lsrc/qemu.git/target/i386/fpu_helper.c:827:5: error: implicit 
declaration of function ‘merge_exception_flags’; did you mean 
‘get_float_exception_flags’? [-Werror=implicit-function-declaration]
     merge_exception_flags(env, old_flags);
     ^~~~~~~~~~~~~~~~~~~~~
     get_float_exception_flags
/home/alex/lsrc/qemu.git/target/i386/fpu_helper.c:827:5: error: nested extern 
declaration of ‘merge_exception_flags’ [-Werror=nested-externs]
cc1: all warnings being treated as errors

-- 
Alex Bennée