[Qemu-devel] [PATCH 04/19] fpu/softfloat: Canonicalize NaN fraction

[Richard Henderson <richard.henderson@linaro.org>]

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