Re: [Qemu-devel] [PATCH 3/4] target-arm: Add support for 'Standard FPSCR Value' as used by Neon

[Aurelien Jarno]

On Fri, Jan 07, 2011 at 09:26:26AM +0000, Peter Maydell wrote:
> Add support to the ARM helper routines for a second fp_status value
> which should be used for operations which the ARM ARM indicates use
> "ARM standard floating-point arithmetic" rather than being controlled
> by the rounding/flush/NaN settings in the FPSCR.
> 
> Signed-off-by: Peter Maydell <address@hidden>
> ---
>  target-arm/cpu.h    |   13 +++++++++++++
>  target-arm/helper.c |    5 +++++
>  2 files changed, 18 insertions(+), 0 deletions(-)

Reviewed-by: Aurelien Jarno <address@hidden>
 
> diff --git a/target-arm/cpu.h b/target-arm/cpu.h
> index 340933e..e501cf5 100644
> --- a/target-arm/cpu.h
> +++ b/target-arm/cpu.h
> @@ -173,7 +173,20 @@ typedef struct CPUARMState {
>          /* scratch space when Tn are not sufficient.  */
>          uint32_t scratch[8];
>  
> +        /* fp_status is the "normal" fp status. standard_fp_status retains
> +         * values corresponding to the ARM "Standard FPSCR Value", ie
> +         * default-NaN, flush-to-zero, round-to-nearest and is used by
> +         * any operations (generally Neon) which the architecture defines
> +         * as controlled by the standard FPSCR value rather than the FPSCR.
> +         *
> +         * To avoid having to transfer exception bits around, we simply
> +         * say that the FPSCR cumulative exception flags are the logical
> +         * OR of the flags in the two fp statuses. This relies on the
> +         * only thing which needs to read the exception flags being
> +         * an explicit FPSCR read.
> +         */
>          float_status fp_status;
> +        float_status standard_fp_status;
>      } vfp;
>      uint32_t exclusive_addr;
>      uint32_t exclusive_val;
> diff --git a/target-arm/helper.c b/target-arm/helper.c
> index ac47de0..d779055 100644
> --- a/target-arm/helper.c
> +++ b/target-arm/helper.c
> @@ -237,6 +237,9 @@ void cpu_reset(CPUARMState *env)
>      env->vfp.xregs[ARM_VFP_FPEXC] = 0;
>      env->cp15.c2_base_mask = 0xffffc000u;
>  #endif
> +    set_flush_to_zero(1, &env->vfp.standard_fp_status);
> +    set_flush_inputs_to_zero(1, &env->vfp.standard_fp_status);
> +    set_default_nan_mode(1, &env->vfp.standard_fp_status);
>      tlb_flush(env, 1);
>  }
>  
> @@ -2256,6 +2259,7 @@ uint32_t HELPER(vfp_get_fpscr)(CPUState *env)
>              | (env->vfp.vec_len << 16)
>              | (env->vfp.vec_stride << 20);
>      i = get_float_exception_flags(&env->vfp.fp_status);
> +    i |= get_float_exception_flags(&env->vfp.standard_fp_status);
>      fpscr |= vfp_exceptbits_from_host(i);
>      return fpscr;
>  }
> @@ -2323,6 +2327,7 @@ void HELPER(vfp_set_fpscr)(CPUState *env, uint32_t val)
>  
>      i = vfp_exceptbits_to_host(val);
>      set_float_exception_flags(i, &env->vfp.fp_status);
> +    set_float_exception_flags(0, &env->vfp.standard_fp_status);
>  }
>  
>  void vfp_set_fpscr(CPUState *env, uint32_t val)
> -- 
> 1.6.3.3
> 
> 
> 

-- 
Aurelien Jarno                          GPG: 1024D/F1BCDB73
address@hidden                 http://www.aurel32.net