softfloat: add APIs to handle alternative sNaN propagation for fmax/fmin

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 only if ft1 == NaN && ft2 == NaN.

The IEEE 754 spec allows both implementation and some architecture such
as riscv choose different defintions 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>
Signed-off-by: Frank Chang <frank.chang@sifive.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20211021160847.2748577-2-frank.chang@sifive.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>

fpu/softfloat-parts.c.inc

@@ -1219,14 +1219,35 @@ static FloatPartsN *partsN(minmax)(FloatPartsN *a, FloatPartsN *b,
 
     if (unlikely(ab_mask & float_cmask_anynan)) {
         /*
-         * For minnum/maxnum, if one operand is a QNaN, and the other
+         * For minNum/maxNum (IEEE 754-2008)
+         * or minimumNumber/maximumNumber (IEEE 754-2019),
+         * if one operand is a QNaN, and the other
          * operand is numerical, then return numerical argument.
          */
-        if ((flags & minmax_isnum)
+        if ((flags & (minmax_isnum | minmax_isnumber))
             && !(ab_mask & float_cmask_snan)
             && (ab_mask & ~float_cmask_qnan)) {
             return is_nan(a->cls) ? b : a;
         }
+
+        /*
+         * In IEEE 754-2019, minNum, maxNum, minNumMag and maxNumMag
+         * are removed and replaced with minimum, minimumNumber, maximum
+         * and maximumNumber.
+         * minimumNumber/maximumNumber behavior for SNaN is changed to:
+         *   If both operands are NaNs, a QNaN is returned.
+         *   If either operand is a SNaN,
+         *   an invalid operation exception is signaled,
+         *   but unless both operands are NaNs,
+         *   the SNaN is otherwise ignored and not converted to a QNaN.
+         */
+        if ((flags & minmax_isnumber)
+            && (ab_mask & float_cmask_snan)
+            && (ab_mask & ~float_cmask_anynan)) {
+            float_raise(float_flag_invalid, s);
+            return is_nan(a->cls) ? b : a;
+        }
+
         return parts_pick_nan(a, b, s);
     }
 

fpu/softfloat.c

@@ -436,6 +436,11 @@ enum {
     minmax_isnum = 2,
     /* Set for the IEEE 754-2008 minNumMag() and minNumMag() operations. */
     minmax_ismag = 4,
+    /*
+     * Set for the IEEE 754-2019 minimumNumber() and maximumNumber()
+     * operations.
+     */
+    minmax_isnumber = 8,
 };
 
 /* Simple helpers for checking if, or what kind of, NaN we have */
@@ -3927,12 +3932,14 @@ static float128 float128_minmax(float128 a, float128 b,
     { return type##_minmax(a, b, s, flags); }
 
 #define MINMAX_2(type) \
-    MINMAX_1(type, max, 0)                                      \
-    MINMAX_1(type, maxnum, minmax_isnum)                        \
-    MINMAX_1(type, maxnummag, minmax_isnum | minmax_ismag)      \
-    MINMAX_1(type, min, minmax_ismin)                           \
-    MINMAX_1(type, minnum, minmax_ismin | minmax_isnum)         \
-    MINMAX_1(type, minnummag, minmax_ismin | minmax_isnum | minmax_ismag)
+    MINMAX_1(type, max, 0)                                                \
+    MINMAX_1(type, maxnum, minmax_isnum)                                  \
+    MINMAX_1(type, maxnummag, minmax_isnum | minmax_ismag)                \
+    MINMAX_1(type, maximum_number, minmax_isnumber)                       \
+    MINMAX_1(type, min, minmax_ismin)                                     \
+    MINMAX_1(type, minnum, minmax_ismin | minmax_isnum)                   \
+    MINMAX_1(type, minnummag, minmax_ismin | minmax_isnum | minmax_ismag) \
+    MINMAX_1(type, minimum_number, minmax_ismin | minmax_isnumber)        \
 
 MINMAX_2(float16)
 MINMAX_2(bfloat16)

include/fpu/softfloat.h

@@ -243,6 +243,8 @@ 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_minimum_number(float16, float16, float_status *status);
+float16 float16_maximum_number(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);
@@ -422,6 +424,8 @@ bfloat16 bfloat16_minnum(bfloat16, bfloat16, float_status *status);
 bfloat16 bfloat16_maxnum(bfloat16, bfloat16, float_status *status);
 bfloat16 bfloat16_minnummag(bfloat16, bfloat16, float_status *status);
 bfloat16 bfloat16_maxnummag(bfloat16, bfloat16, float_status *status);
+bfloat16 bfloat16_minimum_number(bfloat16, bfloat16, float_status *status);
+bfloat16 bfloat16_maximum_number(bfloat16, bfloat16, float_status *status);
 bfloat16 bfloat16_sqrt(bfloat16, float_status *status);
 FloatRelation bfloat16_compare(bfloat16, bfloat16, float_status *status);
 FloatRelation bfloat16_compare_quiet(bfloat16, bfloat16, float_status *status);
@@ -589,6 +593,8 @@ 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_minimum_number(float32, float32, float_status *status);
+float32 float32_maximum_number(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);
@@ -778,6 +784,8 @@ 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_minimum_number(float64, float64, float_status *status);
+float64 float64_maximum_number(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);
@@ -1210,6 +1218,8 @@ float128 float128_minnum(float128, float128, float_status *status);
 float128 float128_maxnum(float128, float128, float_status *status);
 float128 float128_minnummag(float128, float128, float_status *status);
 float128 float128_maxnummag(float128, float128, float_status *status);
+float128 float128_minimum_number(float128, float128, float_status *status);
+float128 float128_maximum_number(float128, float128, float_status *status);
 bool float128_is_quiet_nan(float128, float_status *status);
 bool float128_is_signaling_nan(float128, float_status *status);
 float128 float128_silence_nan(float128, float_status *status);