[Qemu-devel] [PATCH] target/arm: Honour FPCR.FZ in FRECPX

[Qemu-devel] [PATCH] target/arm: Honour FPCR.FZ in FRECPX

[Peter Maydell]

The FRECPX instructions should (like most other floating point operations)
honour the FPCR.FZ bit which specifies whether input denormals should
be flushed to zero (or FZ16 for the half-precision version).
We forgot to implement this, which doesn't affect the results (since
the calculation doesn't actually care about the mantissa bits) but did
mean we were failing to set the FPSR.IDC bit.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
---
 target/arm/helper-a64.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/target/arm/helper-a64.c b/target/arm/helper-a64.c
index f92bdea732..c4d2a04827 100644
--- a/target/arm/helper-a64.c
+++ b/target/arm/helper-a64.c
@@ -384,6 +384,8 @@ float16 HELPER(frecpx_f16)(float16 a, void *fpstp)
         return nan;
     }
 
+    a = float16_squash_input_denormal(a, fpst);
+
     val16 = float16_val(a);
     sbit = 0x8000 & val16;
     exp = extract32(val16, 10, 5);
@@ -413,6 +415,8 @@ float32 HELPER(frecpx_f32)(float32 a, void *fpstp)
         return nan;
     }
 
+    a = float32_squash_input_denormal(a, fpst);
+
     val32 = float32_val(a);
     sbit = 0x80000000ULL & val32;
     exp = extract32(val32, 23, 8);
@@ -442,6 +446,8 @@ float64 HELPER(frecpx_f64)(float64 a, void *fpstp)
         return nan;
     }
 
+    a = float64_squash_input_denormal(a, fpst);
+
     val64 = float64_val(a);
     sbit = 0x8000000000000000ULL & val64;
     exp = extract64(float64_val(a), 52, 11);
-- 
2.17.0

Re: [Qemu-devel] [PATCH] target/arm: Honour FPCR.FZ in FRECPX

[Richard Henderson]

On 05/21/2018 10:27 AM, Peter Maydell wrote:
> The FRECPX instructions should (like most other floating point operations)
> honour the FPCR.FZ bit which specifies whether input denormals should
> be flushed to zero (or FZ16 for the half-precision version).
> We forgot to implement this, which doesn't affect the results (since
> the calculation doesn't actually care about the mantissa bits) but did
> mean we were failing to set the FPSR.IDC bit.
> 
> Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
> ---
>  target/arm/helper-a64.c | 6 ++++++
>  1 file changed, 6 insertions(+)

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>

r~