Re: [Qemu-devel] [PATCH v5 1/5] fpu: softfloat: Add normalize_roundpack_float32 function

[Chen Gang <chengang@emindsoft.com.cn>]

For sig == 0 case, the original implementation is incorrect (although it
passes gcc testsuite), it needs to consider about sign for float_zero.

The related fix diff for it is below. After patches v5 are finished
reviewing, I shall merge the fix diff below to patch v6, next.

Thanks.

diff --git a/fpu/softfloat.c b/fpu/softfloat.c
index dba8566..5ad8bb5 100644
--- a/fpu/softfloat.c
+++ b/fpu/softfloat.c
@@ -7098,19 +7098,15 @@ float32 normalize_roundpack_float32(flag sign, int_fast16_t exp, uint32_t sig,
         return packFloat32(sign, 0, sig);
     }
 
+    if (!sig) {
+        return float32_set_sign(float32_zero, sign);
+    }
+
     if (sign) {
         if (sig & 0x7FFFFFFF) {
             return normalizeRoundAndPackFloat32(1, exp - 2, sig, status);
         }
-        if (sig) {
-            return packFloat32(1, exp, 0);
-        } else {
-            return float32_zero;
-        }
-    }
-
-    if (!sig) {
-        return float32_zero;
+        return packFloat32(1, exp, 0);
     }
 
     scount = countLeadingZeros64(absa) - 40;

On 1/3/16 06:25, chengang@emindsoft.com.cn wrote:
> From: Chen Gang <gang.chen.5i5j@gmail.com>
> 
> It is based on (u)int32_to_float32 function to support float32 packing.
> 
> Signed-off-by: Chen Gang <gang.chen.5i5j@gmail.com>
> ---
>  fpu/softfloat.c         | 55 +++++++++++++++++++++++++++++++++++++++++++++++++
>  include/fpu/softfloat.h |  8 +++++++
>  2 files changed, 63 insertions(+)
> 
> diff --git a/fpu/softfloat.c b/fpu/softfloat.c
> index f1170fe..dba8566 100644
> --- a/fpu/softfloat.c
> +++ b/fpu/softfloat.c
> @@ -7080,6 +7080,61 @@ float64 uint32_to_float64(uint32_t a, float_status *status)
>      return int64_to_float64(a, status);
>  }
>  
> +/*
> + * The mantissa contents the hide bit, e.g. exp: 0x9e with sig: 1 means 1.0f.
> + *
> + * It references from int32_to_float32() and uint32_to_float32()
> + */
> +float32 normalize_roundpack_float32(flag sign, int_fast16_t exp, uint32_t sig,
> +                                    float_status *status)
> +{
> +    uint64_t absa = sig;
> +    int8_t scount;
> +
> +    if (exp >= 0xff) {
> +        return packFloat32(sign, 0xFF, 0);
> +    } else if (exp <= 0) {
> +        shift32RightJamming(sig, 0 - exp, &sig);
> +        return packFloat32(sign, 0, sig);
> +    }
> +
> +    if (sign) {
> +        if (sig & 0x7FFFFFFF) {
> +            return normalizeRoundAndPackFloat32(1, exp - 2, sig, status);
> +        }
> +        if (sig) {
> +            return packFloat32(1, exp, 0);
> +        } else {
> +            return float32_zero;
> +        }
> +    }
> +
> +    if (!sig) {
> +        return float32_zero;
> +    }
> +
> +    scount = countLeadingZeros64(absa) - 40;
> +    if (scount >= 0) {
> +        exp -= 7 + scount + 2;
> +        if (exp <= 0) {
> +            return packFloat32(0, 0, absa);
> +        }
> +        return packFloat32(0, exp, absa << scount);
> +    }
> +
> +    scount += 7;
> +    exp -= scount + 2;
> +    if (exp <= 0) {
> +        return packFloat32(0, 0, absa);
> +    }
> +    if (scount < 0) {
> +        shift64RightJamming(absa, 0 - scount, &absa);
> +    } else {
> +        absa <<= scount;
> +    }
> +    return roundAndPackFloat32(0, exp, absa, status);
> +}
> +
>  uint32 float32_to_uint32(float32 a, float_status *status)
>  {
>      int64_t v;
> diff --git a/include/fpu/softfloat.h b/include/fpu/softfloat.h
> index ded34eb..4995a15 100644
> --- a/include/fpu/softfloat.h
> +++ b/include/fpu/softfloat.h
> @@ -422,6 +422,14 @@ int float32_is_signaling_nan( float32 );
>  float32 float32_maybe_silence_nan( float32 );
>  float32 float32_scalbn(float32, int, float_status *status);
>  
> +/*
> + * The mantissa contents the hide bit, e.g. exp: 0x9e with sig: 1 means 1.0f.
> + *
> + * It references from int32_to_float32() and uint32_to_float32()
> + */
> +float32 normalize_roundpack_float32(flag sign, int_fast16_t exp, uint32_t sig,
> +                                    float_status *status);
> +
>  static inline float32 float32_abs(float32 a)
>  {
>      /* Note that abs does *not* handle NaN specially, nor does
> 

-- 
Chen Gang (陈刚)

Open, share, and attitude like air, water, and life which God blessed