[Qemu-devel] [V5 PATCH 03/22] softfloat: Fix float64_to_uint64_round_to_zero

[Tom Musta <tommusta@gmail.com>]

The float64_to_uint64_round_to_zero routine is incorrect.

For example, the following test pattern:

    46697351FF4AEC29 / 0x1.97351ff4aec29p+103

currently produces 8000000000000000 instead of FFFFFFFFFFFFFFFF.

This patch re-implements the routine to temporarily force the
rounding mode and use the float64_to_uint64 routine.

This contribution can be licensed under either the softfloat-2a or -2b
license.

Signed-off-by: Tom Musta <tommusta@gmail.com>
---
 fpu/softfloat.c |   12 +++++-------
 1 files changed, 5 insertions(+), 7 deletions(-)

diff --git a/fpu/softfloat.c b/fpu/softfloat.c
index 9f42a5b..67ee37b 100644
--- a/fpu/softfloat.c
+++ b/fpu/softfloat.c
@@ -6681,13 +6681,11 @@ uint64_t float64_to_uint64(float64 a STATUS_PARAM)
 
 uint64_t float64_to_uint64_round_to_zero (float64 a STATUS_PARAM)
 {
-    int64_t v;
-
-    v = float64_val(int64_to_float64(INT64_MIN STATUS_VAR));
-    v += float64_val(a);
-    v = float64_to_int64_round_to_zero(make_float64(v) STATUS_VAR);
-
-    return v - INT64_MIN;
+    signed char current_rounding_mode = STATUS(float_rounding_mode);
+    set_float_rounding_mode(float_round_to_zero STATUS_VAR);
+    int64_t v = float64_to_uint64(a STATUS_VAR);
+    set_float_rounding_mode(current_rounding_mode STATUS_VAR);
+    return v;
 }
 
 #define COMPARE(s, nan_exp)                                                  \
-- 
1.7.1