Patchwork [2/4] target-arm: Fix implementation of VRSQRTS

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Submitter Peter Maydell
Date Jan. 7, 2011, 9:26 a.m.
Message ID <1294392387-24300-3-git-send-email-peter.maydell@linaro.org>
Download mbox | patch
Permalink /patch/77860/
State New
Headers show

Comments

Peter Maydell - Jan. 7, 2011, 9:26 a.m.
The implementation of the ARM VRSQRTS instruction (which calculates
(3 - op1 * op2) / 2) was missing the division operation. It also
did not handle the special cases of (0,inf) and (inf,0).

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
---
 target-arm/helper.c |   10 +++++++++-
 1 files changed, 9 insertions(+), 1 deletions(-)
Aurelien Jarno - Jan. 10, 2011, 7:20 p.m.
On Fri, Jan 07, 2011 at 09:26:25AM +0000, Peter Maydell wrote:
> The implementation of the ARM VRSQRTS instruction (which calculates
> (3 - op1 * op2) / 2) was missing the division operation. It also
> did not handle the special cases of (0,inf) and (inf,0).
> 
> Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
> ---
>  target-arm/helper.c |   10 +++++++++-
>  1 files changed, 9 insertions(+), 1 deletions(-)

Reviewed-by: Aurelien Jarno <aurelien@aurel32.net>

> diff --git a/target-arm/helper.c b/target-arm/helper.c
> index 705b99f..ac47de0 100644
> --- a/target-arm/helper.c
> +++ b/target-arm/helper.c
> @@ -2612,8 +2612,16 @@ float32 HELPER(recps_f32)(float32 a, float32 b, CPUState *env)
>  float32 HELPER(rsqrts_f32)(float32 a, float32 b, CPUState *env)
>  {
>      float_status *s = &env->vfp.fp_status;
> +    float32 two = int32_to_float32(2, s);
>      float32 three = int32_to_float32(3, s);
> -    return float32_sub(three, float32_mul(a, b, s), s);
> +    float32 product;
> +    if ((float32_is_infinity(a) && float32_is_zero_or_denormal(b)) ||
> +        (float32_is_infinity(b) && float32_is_zero_or_denormal(a))) {
> +        product = float32_zero;
> +    } else {
> +        product = float32_mul(a, b, s);
> +    }
> +    return float32_div(float32_sub(three, product, s), two, s);
>  }
>  
>  /* NEON helpers.  */
> -- 
> 1.6.3.3
> 
> 
>

Patch

diff --git a/target-arm/helper.c b/target-arm/helper.c
index 705b99f..ac47de0 100644
--- a/target-arm/helper.c
+++ b/target-arm/helper.c
@@ -2612,8 +2612,16 @@  float32 HELPER(recps_f32)(float32 a, float32 b, CPUState *env)
 float32 HELPER(rsqrts_f32)(float32 a, float32 b, CPUState *env)
 {
     float_status *s = &env->vfp.fp_status;
+    float32 two = int32_to_float32(2, s);
     float32 three = int32_to_float32(3, s);
-    return float32_sub(three, float32_mul(a, b, s), s);
+    float32 product;
+    if ((float32_is_infinity(a) && float32_is_zero_or_denormal(b)) ||
+        (float32_is_infinity(b) && float32_is_zero_or_denormal(a))) {
+        product = float32_zero;
+    } else {
+        product = float32_mul(a, b, s);
+    }
+    return float32_div(float32_sub(three, product, s), two, s);
 }
 
 /* NEON helpers.  */