[Qemu-arm] [PATCH v6 6/9] target-mips: Activate IEEE 754-2008 signaling NaN bit meaning

[Aleksandar Markovic]

From: Aleksandar Markovic <address@hidden>

Functions mips_cpu_reset() and msa_reset() are updated so that flag
snan_bit_is_one is properly set for any Mips FPU/MSA configuration.
For main FPUs, CPUs with FCR31's FCR31_NAN2008 bit set will invoke
set_snan_bit_is_one(0). For MSA, as it is IEEE 274-2008 compliant
from it inception, set_snan_bit_is_one(0) will always be invoked.

By applying this patch, a number of incorrect behaviors for CPU
configurations that require IEEE 754-2008 compliance will be fixed.
Those are behaviors that (up to the moment of applying this patch)
did not get the desired functionality from SoftFloat library with
respect to distinguishing between quiet and signaling NaN, getting
default NaN values (both quiet and signaling), establishing if a
floating point number is Nan or not, etc.

Two examples:

* <MAX|MAXA>.<D|S> will now correctly detect and propagate NaNs.
* CLASS.<D|S> and FCLASS.<D|S> will now correcty detect NaN flavors.

Signed-off-by: Thomas Schwinge <address@hidden>
Signed-off-by: Maciej W. Rozycki <address@hidden>
Signed-off-by: Aleksandar Markovic <address@hidden>
---
 target-mips/translate.c      | 6 +++++-
 target-mips/translate_init.c | 3 ++-
 2 files changed, 7 insertions(+), 2 deletions(-)

diff --git a/target-mips/translate.c b/target-mips/translate.c
index e934884..2cdd2bd 100644
--- a/target-mips/translate.c
+++ b/target-mips/translate.c
@@ -20129,7 +20129,11 @@ void cpu_state_reset(CPUMIPSState *env)
     env->CP0_PageGrain = env->cpu_model->CP0_PageGrain;
     env->active_fpu.fcr0 = env->cpu_model->CP1_fcr0;
     env->active_fpu.fcr31 = env->cpu_model->CP1_fcr31;
-    set_snan_bit_is_one(1, &env->active_fpu.fp_status);
+    if ((env->active_fpu.fcr31 >> FCR31_NAN2008) & 1) {
+        set_snan_bit_is_one(0, &env->active_fpu.fp_status);
+    } else {
+        set_snan_bit_is_one(1, &env->active_fpu.fp_status);
+    }
     env->msair = env->cpu_model->MSAIR;
     env->insn_flags = env->cpu_model->insn_flags;
 
diff --git a/target-mips/translate_init.c b/target-mips/translate_init.c
index e81a831..a37d8bb 100644
--- a/target-mips/translate_init.c
+++ b/target-mips/translate_init.c
@@ -893,5 +893,6 @@ static void msa_reset(CPUMIPSState *env)
     /* clear float_status nan mode */
     set_default_nan_mode(0, &env->active_tc.msa_fp_status);
 
-    set_snan_bit_is_one(1, &env->active_tc.msa_fp_status);
+    /* set proper signanling bit meaning ("1" means "quiet") */
+    set_snan_bit_is_one(0, &env->active_tc.msa_fp_status);
 }
-- 
1.9.1