softfloat: Fix uint64_to_float64

The interface to normalizeRoundAndPackFloat64 requires that the
high bit be clear.  Perform one shift-right-and-jam if needed.

Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Richard Henderson <rth@twiddle.net>
Signed-off-by: Blue Swirl <blauwirbel@gmail.com>

1 files changed, 10 insertions, 3 deletions

diff --git a/fpu/softfloat.c b/fpu/softfloat.c
index 0cfa6b4831..20b05d4392 100644
--- a/fpu/softfloat.c
+++ b/fpu/softfloat.c
@@ -1271,11 +1271,18 @@ float64 int64_to_float64( int64 a STATUS_PARAM )
 
 }
 
-float64 uint64_to_float64( uint64 a STATUS_PARAM )
+float64 uint64_to_float64(uint64 a STATUS_PARAM)
 {
-    if ( a == 0 ) return float64_zero;
-    return normalizeRoundAndPackFloat64( 0, 0x43C, a STATUS_VAR );
+    int exp =  0x43C;
 
+    if (a == 0) {
+        return float64_zero;
+    }
+    if ((int64_t)a < 0) {
+        shift64RightJamming(a, 1, &a);
+        exp += 1;
+    }
+    return normalizeRoundAndPackFloat64(0, exp, a STATUS_VAR);
 }
 
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