Shift the NaN fraction to a canonical position, much like we do
for the fraction of normal numbers.  Immediately, this simplifies
the float-to-float conversion.  Later, this will facilitate
manipulation of NaNs within the shared code paths.

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
---
 fpu/softfloat.c | 13 ++++++-------
 1 file changed, 6 insertions(+), 7 deletions(-)

diff --git a/fpu/softfloat.c b/fpu/softfloat.c
index 5e4982b035..df377b6314 100644
--- a/fpu/softfloat.c
+++ b/fpu/softfloat.c
@@ -329,10 +329,11 @@ static FloatParts canonicalize(FloatParts part, const FloatFmt *parm,
         if (part.frac == 0) {
             part.cls = float_class_inf;
         } else {
+            part.frac <<= parm->frac_shift;
 #ifdef NO_SIGNALING_NANS
             part.cls = float_class_qnan;
 #else
-            int64_t msb = part.frac << (parm->frac_shift + 2);
+            int64_t msb = part.frac << 2;
             if ((msb < 0) == status->snan_bit_is_one) {
                 part.cls = float_class_snan;
             } else {
@@ -498,6 +499,7 @@ static FloatParts round_canonical(FloatParts p, float_status *s,
     case float_class_qnan:
     case float_class_snan:
         exp = exp_max;
+        frac >>= parm->frac_shift;
         break;
 
     default:
@@ -1264,13 +1266,10 @@ static FloatParts float_to_float(FloatParts a,
         }
 
         /*
-         * Our only option now is to "re-pack" the NaN. As the
-         * canonilization process doesn't mess with fraction bits for
-         * NaNs we do it all here. We also reset a.exp to the
-         * destination format exp_max as the maybe_silence_nan code
-         * assumes it is correct (which is would be for non-conversions).
+         * Reset a.exp to the destination format exp_max as
+         * the maybe_silence_nan code assumes it is correct
+         * (which it would be for non-conversions).
          */
-        a.frac = a.frac << (64 - srcf->frac_size) >> (64 - dstf->frac_size);
         a.exp = dstf->exp_max;
         a.cls = float_class_msnan;
     }
-- 
2.17.0

Richard Henderson <richard.henderson@linaro.org> writes:

> Shift the NaN fraction to a canonical position, much like we do
> for the fraction of normal numbers.  Immediately, this simplifies
> the float-to-float conversion.  Later, this will facilitate
> manipulation of NaNs within the shared code paths.
>
> Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
> ---
>  fpu/softfloat.c | 13 ++++++-------
>  1 file changed, 6 insertions(+), 7 deletions(-)
>
> diff --git a/fpu/softfloat.c b/fpu/softfloat.c
> index 5e4982b035..df377b6314 100644
> --- a/fpu/softfloat.c
> +++ b/fpu/softfloat.c
> @@ -329,10 +329,11 @@ static FloatParts canonicalize(FloatParts part, const FloatFmt *parm,
>          if (part.frac == 0) {
>              part.cls = float_class_inf;
>          } else {
> +            part.frac <<= parm->frac_shift;
>  #ifdef NO_SIGNALING_NANS
>              part.cls = float_class_qnan;
>  #else
> -            int64_t msb = part.frac << (parm->frac_shift + 2);
> +            int64_t msb = part.frac << 2;
>              if ((msb < 0) == status->snan_bit_is_one) {
>                  part.cls = float_class_snan;
>              } else {
> @@ -498,6 +499,7 @@ static FloatParts round_canonical(FloatParts p, float_status *s,
>      case float_class_qnan:
>      case float_class_snan:
>          exp = exp_max;
> +        frac >>= parm->frac_shift;

Unfortunately we now miss this step when we handle:

    case float_class_msnan:
        return float64_maybe_silence_nan(float64_pack_raw(p), s);

This seems to fix that:

recanonicalise frac before packing and sending

1 file changed, 3 insertions(+)
fpu/softfloat.c | 3 +++

modified   fpu/softfloat.c
@@ -532,6 +532,7 @@ static float16 float16a_round_pack_canonical(const FloatFmt *params,
     case float_class_dnan:
         return float16_default_nan(s);
     case float_class_msnan:
+        p.frac >>= params->frac_shift;
         return float16_maybe_silence_nan(float16_pack_raw(p), s);
     default:
         p = round_canonical(p, s, params);
@@ -555,6 +556,7 @@ static float32 float32_round_pack_canonical(FloatParts p, float_status *s)
     case float_class_dnan:
         return float32_default_nan(s);
     case float_class_msnan:
+        p.frac >>= float32_params.frac_shift;
         return float32_maybe_silence_nan(float32_pack_raw(p), s);
     default:
         p = round_canonical(p, s, &float32_params);
@@ -573,6 +575,7 @@ static float64 float64_round_pack_canonical(FloatParts p, float_status *s)
     case float_class_dnan:
         return float64_default_nan(s);
     case float_class_msnan:
+        p.frac >>= float64_params.frac_shift;
         return float64_maybe_silence_nan(float64_pack_raw(p), s);
     default:
         p = round_canonical(p, s, &float64_params);

--
Alex Bennée

On 05/11/2018 09:26 AM, Alex Bennée wrote:
> 
> Richard Henderson <richard.henderson@linaro.org> writes:
> 
>> Shift the NaN fraction to a canonical position, much like we do
>> for the fraction of normal numbers.  Immediately, this simplifies
>> the float-to-float conversion.  Later, this will facilitate
>> manipulation of NaNs within the shared code paths.
>>
>> Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
>> ---
>>  fpu/softfloat.c | 13 ++++++-------
>>  1 file changed, 6 insertions(+), 7 deletions(-)
>>
>> diff --git a/fpu/softfloat.c b/fpu/softfloat.c
>> index 5e4982b035..df377b6314 100644
>> --- a/fpu/softfloat.c
>> +++ b/fpu/softfloat.c
>> @@ -329,10 +329,11 @@ static FloatParts canonicalize(FloatParts part, const FloatFmt *parm,
>>          if (part.frac == 0) {
>>              part.cls = float_class_inf;
>>          } else {
>> +            part.frac <<= parm->frac_shift;
>>  #ifdef NO_SIGNALING_NANS
>>              part.cls = float_class_qnan;
>>  #else
>> -            int64_t msb = part.frac << (parm->frac_shift + 2);
>> +            int64_t msb = part.frac << 2;
>>              if ((msb < 0) == status->snan_bit_is_one) {
>>                  part.cls = float_class_snan;
>>              } else {
>> @@ -498,6 +499,7 @@ static FloatParts round_canonical(FloatParts p, float_status *s,
>>      case float_class_qnan:
>>      case float_class_snan:
>>          exp = exp_max;
>> +        frac >>= parm->frac_shift;
> 
> Unfortunately we now miss this step when we handle:
> 
>     case float_class_msnan:
>         return float64_maybe_silence_nan(float64_pack_raw(p), s);
> 
> This seems to fix that:
> 
> recanonicalise frac before packing and sending

Good catch.  Merged for bisection.


r~