fpu/softfloat: Replace float_class_dnan with parts_default_nan

With a canonical representation of NaNs, we can return the
default nan directly rather than delay the expansion until
the final format is known.

Note one case where we uselessly assigned to a.sign, which was
overwritten/ignored later when expanding float_class_dnan.

Tested-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>

1 files changed, 37 insertions, 0 deletions

diff --git a/fpu/softfloat-specialize.h b/fpu/softfloat-specialize.h
index 515cb12cfa..0d3d81a52b 100644
--- a/fpu/softfloat-specialize.h
+++ b/fpu/softfloat-specialize.h
@@ -102,6 +102,43 @@ static bool parts_is_snan_frac(uint64_t frac, float_status *status)
 }
 
 /*----------------------------------------------------------------------------
+| The pattern for a default generated deconstructed floating-point NaN.
+*----------------------------------------------------------------------------*/
+
+static FloatParts parts_default_nan(float_status *status)
+{
+    bool sign = 0;
+    uint64_t frac;
+
+#if defined(TARGET_SPARC) || defined(TARGET_M68K)
+    frac = (1ULL << DECOMPOSED_BINARY_POINT) - 1;
+#elif defined(TARGET_PPC) || defined(TARGET_ARM) || defined(TARGET_ALPHA) || \
+      defined(TARGET_S390X) || defined(TARGET_RISCV)
+    frac = 1ULL << (DECOMPOSED_BINARY_POINT - 1);
+#elif defined(TARGET_HPPA)
+    frac = 1ULL << (DECOMPOSED_BINARY_POINT - 2);
+#else
+    if (status->snan_bit_is_one) {
+        frac = (1ULL << (DECOMPOSED_BINARY_POINT - 1)) - 1;
+    } else {
+#if defined(TARGET_MIPS)
+        frac = 1ULL << (DECOMPOSED_BINARY_POINT - 1);
+#else
+        frac = 1ULL << (DECOMPOSED_BINARY_POINT - 1);
+        sign = 1;
+#endif
+    }
+#endif
+
+    return (FloatParts) {
+        .cls = float_class_qnan,
+        .sign = sign,
+        .exp = INT_MAX,
+        .frac = frac
+    };
+}
+
+/*----------------------------------------------------------------------------
 | The pattern for a default generated half-precision NaN.
 *----------------------------------------------------------------------------*/
 float16 float16_default_nan(float_status *status)