[Qemu-devel] [PATCH 1/7] target-ppc: VXSQRT Should Not Be Set for NaNs

[Tom Musta <tommusta@gmail.com>]

The Power ISA square root instructions (fsqrt[s], frsqrte[s]) must
set the FPSCR[VXSQRT] flag when operating on a negative value.
However, NaNs have no sign and therefore this flag should not
be set when operating on one.

Change the order of the checks in the helper code.  Move the
SNaN-to-QNaN macro to the top of the file so that it can be
re-used.

Signed-off-by: Tom Musta <tommusta@gmail.com>
---
 target-ppc/fpu_helper.c |   29 +++++++++++++++++------------
 1 files changed, 17 insertions(+), 12 deletions(-)

diff --git a/target-ppc/fpu_helper.c b/target-ppc/fpu_helper.c
index da93d12..288401d 100644
--- a/target-ppc/fpu_helper.c
+++ b/target-ppc/fpu_helper.c
@@ -19,6 +19,9 @@
 #include "cpu.h"
 #include "exec/helper-proto.h"
 
+#define float64_snan_to_qnan(x) ((x) | 0x0008000000000000ULL)
+#define float32_snan_to_qnan(x) ((x) | 0x00400000)
+
 /*****************************************************************************/
 /* Floating point operations helpers */
 uint64_t helper_float32_to_float64(CPUPPCState *env, uint32_t arg)
@@ -926,14 +929,16 @@ uint64_t helper_fsqrt(CPUPPCState *env, uint64_t arg)
 
     farg.ll = arg;
 
-    if (unlikely(float64_is_neg(farg.d) && !float64_is_zero(farg.d))) {
-        /* Square root of a negative nonzero number */
-        farg.ll = fload_invalid_op_excp(env, POWERPC_EXCP_FP_VXSQRT, 1);
-    } else {
+    if (unlikely(float64_is_any_nan(farg.d))) {
         if (unlikely(float64_is_signaling_nan(farg.d))) {
-            /* sNaN square root */
+            /* sNaN reciprocal square root */
             fload_invalid_op_excp(env, POWERPC_EXCP_FP_VXSNAN, 1);
+            farg.ll = float64_snan_to_qnan(farg.ll);
         }
+    } else if (unlikely(float64_is_neg(farg.d) && !float64_is_zero(farg.d))) {
+        /* Square root of a negative nonzero number */
+        farg.ll = fload_invalid_op_excp(env, POWERPC_EXCP_FP_VXSQRT, 1);
+    } else {
         farg.d = float64_sqrt(farg.d, &env->fp_status);
     }
     return farg.ll;
@@ -980,17 +985,20 @@ uint64_t helper_frsqrte(CPUPPCState *env, uint64_t arg)
 
     farg.ll = arg;
 
-    if (unlikely(float64_is_neg(farg.d) && !float64_is_zero(farg.d))) {
-        /* Reciprocal square root of a negative nonzero number */
-        farg.ll = fload_invalid_op_excp(env, POWERPC_EXCP_FP_VXSQRT, 1);
-    } else {
+    if (unlikely(float64_is_any_nan(farg.d))) {
         if (unlikely(float64_is_signaling_nan(farg.d))) {
             /* sNaN reciprocal square root */
             fload_invalid_op_excp(env, POWERPC_EXCP_FP_VXSNAN, 1);
+            farg.ll = float64_snan_to_qnan(farg.ll);
         }
+    } else if (unlikely(float64_is_neg(farg.d) && !float64_is_zero(farg.d))) {
+        /* Reciprocal square root of a negative nonzero number */
+        farg.ll = fload_invalid_op_excp(env, POWERPC_EXCP_FP_VXSQRT, 1);
+    } else {
         farg.d = float64_sqrt(farg.d, &env->fp_status);
         farg.d = float64_div(float64_one, farg.d, &env->fp_status);
     }
+
     return farg.ll;
 }
 
@@ -2388,9 +2396,6 @@ void helper_##op(CPUPPCState *env, uint32_t opcode)                      \
 VSX_SCALAR_CMP(xscmpodp, 1)
 VSX_SCALAR_CMP(xscmpudp, 0)
 
-#define float64_snan_to_qnan(x) ((x) | 0x0008000000000000ULL)
-#define float32_snan_to_qnan(x) ((x) | 0x00400000)
-
 /* VSX_MAX_MIN - VSX floating point maximum/minimum
  *   name  - instruction mnemonic
  *   op    - operation (max or min)
-- 
1.7.1