[Qemu-devel] [RFC PATCH v2 1/2] softfloat: Handle float64 rounding properly for underflow case

[Bharata B Rao]

When rounding a floating point result to float64 precision, the
existing code doesn't re-calculate the required round increment
for the underflow case. Fix this.

Signed-off-by: Bharata B Rao <address@hidden>
---
 fpu/softfloat.c | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/fpu/softfloat.c b/fpu/softfloat.c
index c295f31..b04699c 100644
--- a/fpu/softfloat.c
+++ b/fpu/softfloat.c
@@ -651,6 +651,23 @@ static float64 roundAndPackFloat64(flag zSign, int zExp, 
uint64_t zSig,
             if (isTiny && roundBits) {
                 float_raise(float_flag_underflow, status);
             }
+            switch (roundingMode) {
+            case float_round_nearest_even:
+            case float_round_ties_away:
+                roundIncrement = 0x200;
+                break;
+            case float_round_to_zero:
+                roundIncrement = 0;
+                break;
+            case float_round_up:
+                roundIncrement = zSign ? 0 : 0x3ff;
+                break;
+            case float_round_down:
+                roundIncrement = zSign ? 0x3ff : 0;
+                break;
+            default:
+                abort();
+            }
         }
     }
     if (roundBits) {
-- 
2.7.4