softfloat: Fix single-to-half precision float conversions

Fix various bugs in the single-to-half-precision conversion code:
 * input NaNs not correctly converted in IEEE mode
   (fixed by defining and using a commonNaNToFloat16())
 * wrong values returned when converting NaN/Inf into non-IEEE
   half precision value
 * wrong values returned for conversion of values which are
   on the boundary between denormal and zero for the half
   precision format
 * zeroes not correctly identified
 * excessively large results in non-IEEE mode should
   generate InvalidOp, not Overflow

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Aurelien Jarno <aurelien@aurel32.net>

1 files changed, 21 insertions, 0 deletions

diff --git a/fpu/softfloat-specialize.h b/fpu/softfloat-specialize.h
index 1b7521f8e6..1c0b12b573 100644
--- a/fpu/softfloat-specialize.h
+++ b/fpu/softfloat-specialize.h
@@ -120,6 +120,27 @@ float16 float16_maybe_silence_nan(float16 a_)
 }
 
 /*----------------------------------------------------------------------------
+| Returns the result of converting the canonical NaN `a' to the half-
+| precision floating-point format.
+*----------------------------------------------------------------------------*/
+
+static float16 commonNaNToFloat16(commonNaNT a STATUS_PARAM)
+{
+    uint16_t mantissa = a.high>>54;
+
+    if (STATUS(default_nan_mode)) {
+        return float16_default_nan;
+    }
+
+    if (mantissa) {
+        return make_float16(((((uint16_t) a.sign) << 15)
+                             | (0x1F << 10) | mantissa));
+    } else {
+        return float16_default_nan;
+    }
+}
+
+/*----------------------------------------------------------------------------
 | The pattern for a default generated single-precision NaN.
 *----------------------------------------------------------------------------*/
 #if defined(TARGET_SPARC)