[PULL 052/101] target/ppc: Update fres to new flags and float64r32

[Cédric Le Goater]

From: Richard Henderson <richard.henderson@linaro.org>

There is no double-rounding bug here, because the result is
merely an estimate to within 1 part in 256, but perform the
operation with float64r32_div for consistency.

Use float_flag_invalid_snan instead of recomputing the
snan-ness of the operand.

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20211119160502.17432-34-richard.henderson@linaro.org>
Signed-off-by: Cédric Le Goater <clg@kaod.org>
---
 target/ppc/fpu_helper.c | 20 ++++++++++----------
 1 file changed, 10 insertions(+), 10 deletions(-)

diff --git a/target/ppc/fpu_helper.c b/target/ppc/fpu_helper.c
index 83c8f2556cc7..c955b20739ac 100644
--- a/target/ppc/fpu_helper.c
+++ b/target/ppc/fpu_helper.c
@@ -861,20 +861,20 @@ float64 helper_fre(CPUPPCState *env, float64 arg)
 /* fres - fres. */
 uint64_t helper_fres(CPUPPCState *env, uint64_t arg)
 {
-    CPU_DoubleU farg;
-    float32 f32;
-
-    farg.ll = arg;
+    /* "Estimate" the reciprocal with actual division.  */
+    float64 ret = float64r32_div(float64_one, arg, &env->fp_status);
+    int flags = get_float_exception_flags(&env->fp_status);
 
-    if (unlikely(float64_is_signaling_nan(farg.d, &env->fp_status))) {
-        /* sNaN reciprocal */
+    if (unlikely(flags & float_flag_invalid_snan)) {
         float_invalid_op_vxsnan(env, GETPC());
     }
-    farg.d = float64_div(float64_one, farg.d, &env->fp_status);
-    f32 = float64_to_float32(farg.d, &env->fp_status);
-    farg.d = float32_to_float64(f32, &env->fp_status);
+    if (unlikely(flags & float_flag_divbyzero)) {
+        float_zero_divide_excp(env, GETPC());
+        /* For FPSCR.ZE == 0, the result is 1/2.  */
+        ret = float64_set_sign(float64_half, float64_is_neg(arg));
+    }
 
-    return farg.ll;
+    return ret;
 }
 
 /* frsqrte  - frsqrte. */
-- 
2.31.1