diff mbox series

[2/3] softfloat: add APIs to handle alternative sNaN propagation

Message ID 1596102747-20226-3-git-send-email-chihmin.chao@sifive.com (mailing list archive)
State New, archived
Headers show
Series float16 APIs and alternative sNaN handling | expand

Commit Message

Chih-Min Chao July 30, 2020, 9:52 a.m. UTC 
For "fmax/fmin ft0, ft1, ft2" and if one of the inputs is sNaN,
  The original logic
    return NaN and set invalid flag if ft1 == sNaN || ft2 == sNan

  The alternative path
    set invalid flag if ft1 == sNaN || ft2 == sNaN
    return NaN if ft1 == sNaN && ft2 == sNaN

   The ieee754 spec allows both implementation and some architecture such
   as riscv choose differenct defintion in two spec versions.
   (riscv-spec-v2.2 use original version, riscv-spec-20191213 changes to
    alternative)

Signed-off-by: Chih-Min Chao <chihmin.chao@sifive.com>
---
 fpu/softfloat.c         | 75 +++++++++++++++++++++++++++++++------------------
 include/fpu/softfloat.h |  6 ++++
 2 files changed, 54 insertions(+), 27 deletions(-)

Comments

Richard Henderson Aug. 13, 2020, 5:21 p.m. UTC | #1 
On 7/30/20 2:52 AM, Chih-Min Chao wrote:
> For "fmax/fmin ft0, ft1, ft2" and if one of the inputs is sNaN,
>   The original logic
>     return NaN and set invalid flag if ft1 == sNaN || ft2 == sNan
> 
>   The alternative path
>     set invalid flag if ft1 == sNaN || ft2 == sNaN
>     return NaN if ft1 == sNaN && ft2 == sNaN
> 
>    The ieee754 spec allows both implementation and some architecture such
>    as riscv choose differenct defintion in two spec versions.
>    (riscv-spec-v2.2 use original version, riscv-spec-20191213 changes to
>     alternative)
> 
> Signed-off-by: Chih-Min Chao <chihmin.chao@sifive.com>

If both ft1 and ft2 are SNaN, surely the returned result is silenced?  That is
something that is handled by pick_nan, but is not handled here.

Also, the patch subject should be modified to emphasize that this only applies
to min/max and not propagation of all SNaN.


r~
Chih-Min Chao Aug. 14, 2020, 8:59 a.m. UTC | #2 
On Fri, Aug 14, 2020 at 1:21 AM Richard Henderson <
richard.henderson@linaro.org> wrote:

> On 7/30/20 2:52 AM, Chih-Min Chao wrote:
> > For "fmax/fmin ft0, ft1, ft2" and if one of the inputs is sNaN,
> >   The original logic
> >     return NaN and set invalid flag if ft1 == sNaN || ft2 == sNan
> >
> >   The alternative path
> >     set invalid flag if ft1 == sNaN || ft2 == sNaN
> >     return NaN if ft1 == sNaN && ft2 == sNaN
> >
> >    The ieee754 spec allows both implementation and some architecture such
> >    as riscv choose differenct defintion in two spec versions.
> >    (riscv-spec-v2.2 use original version, riscv-spec-20191213 changes to
> >     alternative)
> >
> > Signed-off-by: Chih-Min Chao <chihmin.chao@sifive.com>
>
> If both ft1 and ft2 are SNaN, surely the returned result is silenced?
> That is
> something that is handled by pick_nan, but is not handled here.
>
 Yes, it returns the default_nan, qNaN.


>
> Also, the patch subject should be modified to emphasize that this only
> applies
> to min/max and not propagation of all SNaN.
>
> Will be fixed in the next version.
By the way,  the other patches have been queued in softfloat-next.
Do I need to resend the other two patches in the next version or just this
one ?

Chih-Min Chao

>

>
> r~
>
>
>
Richard Henderson Aug. 14, 2020, 4:15 p.m. UTC | #3 
On 8/14/20 1:59 AM, Chih-Min Chao wrote:
> By the way,  the other patches have been queued in softfloat-next. 
> Do I need to resend the other two patches in the next version or just this one ?

Just this one.  Thanks.


r~
diff mbox series

Patch

diff --git a/fpu/softfloat.c b/fpu/softfloat.c
index 79be4f5..4466ece 100644
--- a/fpu/softfloat.c
+++ b/fpu/softfloat.c
@@ -870,11 +870,16 @@  static FloatParts return_nan(FloatParts a, float_status *s)
     return a;
 }
 
-static FloatParts pick_nan(FloatParts a, FloatParts b, float_status *s)
+static void set_snan_flag(FloatParts a, FloatParts b, float_status *s)
 {
     if (is_snan(a.cls) || is_snan(b.cls)) {
         s->float_exception_flags |= float_flag_invalid;
     }
+}
+
+static FloatParts pick_nan(FloatParts a, FloatParts b, float_status *s)
+{
+    set_snan_flag(a, b, s);
 
     if (s->default_nan_mode) {
         return parts_default_nan(s);
@@ -2743,23 +2748,32 @@  float64 uint16_to_float64(uint16_t a, float_status *status)
  * and minNumMag() from the IEEE-754 2008.
  */
 static FloatParts minmax_floats(FloatParts a, FloatParts b, bool ismin,
-                                bool ieee, bool ismag, float_status *s)
+                                bool ieee, bool ismag, bool issnan_prop,
+                                float_status *s)
 {
     if (unlikely(is_nan(a.cls) || is_nan(b.cls))) {
         if (ieee) {
             /* Takes two floating-point values `a' and `b', one of
              * which is a NaN, and returns the appropriate NaN
              * result. If either `a' or `b' is a signaling NaN,
-             * the invalid exception is raised.
+             * the invalid exception is raised but the NaN
+             * propagation is 'shall'.
              */
             if (is_snan(a.cls) || is_snan(b.cls)) {
-                return pick_nan(a, b, s);
-            } else if (is_nan(a.cls) && !is_nan(b.cls)) {
+                if (issnan_prop) {
+                    return pick_nan(a, b, s);
+                } else {
+                    set_snan_flag(a, b, s);
+                }
+            }
+
+            if (is_nan(a.cls) && !is_nan(b.cls)) {
                 return b;
             } else if (is_nan(b.cls) && !is_nan(a.cls)) {
                 return a;
             }
         }
+
         return pick_nan(a, b, s);
     } else {
         int a_exp, b_exp;
@@ -2813,37 +2827,44 @@  static FloatParts minmax_floats(FloatParts a, FloatParts b, bool ismin,
     }
 }
 
-#define MINMAX(sz, name, ismin, isiee, ismag)                           \
+#define MINMAX(sz, name, ismin, isiee, ismag, issnan_prop)              \
 float ## sz float ## sz ## _ ## name(float ## sz a, float ## sz b,      \
                                      float_status *s)                   \
 {                                                                       \
     FloatParts pa = float ## sz ## _unpack_canonical(a, s);             \
     FloatParts pb = float ## sz ## _unpack_canonical(b, s);             \
-    FloatParts pr = minmax_floats(pa, pb, ismin, isiee, ismag, s);      \
+    FloatParts pr = minmax_floats(pa, pb, ismin, isiee, ismag,          \
+                                  issnan_prop, s);                      \
                                                                         \
     return float ## sz ## _round_pack_canonical(pr, s);                 \
 }
 
-MINMAX(16, min, true, false, false)
-MINMAX(16, minnum, true, true, false)
-MINMAX(16, minnummag, true, true, true)
-MINMAX(16, max, false, false, false)
-MINMAX(16, maxnum, false, true, false)
-MINMAX(16, maxnummag, false, true, true)
-
-MINMAX(32, min, true, false, false)
-MINMAX(32, minnum, true, true, false)
-MINMAX(32, minnummag, true, true, true)
-MINMAX(32, max, false, false, false)
-MINMAX(32, maxnum, false, true, false)
-MINMAX(32, maxnummag, false, true, true)
-
-MINMAX(64, min, true, false, false)
-MINMAX(64, minnum, true, true, false)
-MINMAX(64, minnummag, true, true, true)
-MINMAX(64, max, false, false, false)
-MINMAX(64, maxnum, false, true, false)
-MINMAX(64, maxnummag, false, true, true)
+MINMAX(16, min, true, false, false, true)
+MINMAX(16, minnum, true, true, false, true)
+MINMAX(16, minnum_noprop, true, true, false, false)
+MINMAX(16, minnummag, true, true, true, true)
+MINMAX(16, max, false, false, false, true)
+MINMAX(16, maxnum, false, true, false, true)
+MINMAX(16, maxnum_noprop, false, true, false, false)
+MINMAX(16, maxnummag, false, true, true, true)
+
+MINMAX(32, min, true, false, false, true)
+MINMAX(32, minnum, true, true, false, true)
+MINMAX(32, minnum_noprop, true, true, false, false)
+MINMAX(32, minnummag, true, true, true, true)
+MINMAX(32, max, false, false, false, true)
+MINMAX(32, maxnum, false, true, false, true)
+MINMAX(32, maxnum_noprop, false, true, false, false)
+MINMAX(32, maxnummag, false, true, true, true)
+
+MINMAX(64, min, true, false, false, true)
+MINMAX(64, minnum, true, true, false, true)
+MINMAX(64, minnum_noprop, true, true, false, false)
+MINMAX(64, minnummag, true, true, true, true)
+MINMAX(64, max, false, false, false, true)
+MINMAX(64, maxnum, false, true, false, true)
+MINMAX(64, maxnum_noprop, false, true, false, false)
+MINMAX(64, maxnummag, false, true, true, true)
 
 #undef MINMAX
 
diff --git a/include/fpu/softfloat.h b/include/fpu/softfloat.h
index 573fce9..65842b0 100644
--- a/include/fpu/softfloat.h
+++ b/include/fpu/softfloat.h
@@ -231,6 +231,8 @@  float16 float16_minnum(float16, float16, float_status *status);
 float16 float16_maxnum(float16, float16, float_status *status);
 float16 float16_minnummag(float16, float16, float_status *status);
 float16 float16_maxnummag(float16, float16, float_status *status);
+float16 float16_minnum_noprop(float16, float16, float_status *status);
+float16 float16_maxnum_noprop(float16, float16, float_status *status);
 float16 float16_sqrt(float16, float_status *status);
 FloatRelation float16_compare(float16, float16, float_status *status);
 FloatRelation float16_compare_quiet(float16, float16, float_status *status);
@@ -392,6 +394,8 @@  float32 float32_minnum(float32, float32, float_status *status);
 float32 float32_maxnum(float32, float32, float_status *status);
 float32 float32_minnummag(float32, float32, float_status *status);
 float32 float32_maxnummag(float32, float32, float_status *status);
+float32 float32_minnum_noprop(float32, float32, float_status *status);
+float32 float32_maxnum_noprop(float32, float32, float_status *status);
 bool float32_is_quiet_nan(float32, float_status *status);
 bool float32_is_signaling_nan(float32, float_status *status);
 float32 float32_silence_nan(float32, float_status *status);
@@ -581,6 +585,8 @@  float64 float64_minnum(float64, float64, float_status *status);
 float64 float64_maxnum(float64, float64, float_status *status);
 float64 float64_minnummag(float64, float64, float_status *status);
 float64 float64_maxnummag(float64, float64, float_status *status);
+float64 float64_minnum_noprop(float64, float64, float_status *status);
+float64 float64_maxnum_noprop(float64, float64, float_status *status);
 bool float64_is_quiet_nan(float64 a, float_status *status);
 bool float64_is_signaling_nan(float64, float_status *status);
 float64 float64_silence_nan(float64, float_status *status);