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[v2,for-10.0,43/54] target/mips: Set default NaN pattern explicitly

Message ID 20241202131347.498124-44-peter.maydell@linaro.org
State Superseded
Headers show
Series fpu: Remove pickNaNMulAdd, default-NaN ifdefs | expand

Commit Message

Peter Maydell Dec. 2, 2024, 1:13 p.m. UTC 
Set the default NaN pattern explicitly for MIPS. Note that this
is our only target which currently changes the default NaN
at runtime (which it was previously doing indirectly when it
changed the snan_bit_is_one setting).

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
---
 target/mips/fpu_helper.h | 7 +++++++
 target/mips/msa.c        | 3 +++
 2 files changed, 10 insertions(+)

Comments

Richard Henderson Dec. 2, 2024, 5:31 p.m. UTC | #1 
On 12/2/24 07:13, Peter Maydell wrote:
> Set the default NaN pattern explicitly for MIPS. Note that this
> is our only target which currently changes the default NaN
> at runtime (which it was previously doing indirectly when it
> changed the snan_bit_is_one setting).
> 
> Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
> ---
>   target/mips/fpu_helper.h | 7 +++++++
>   target/mips/msa.c        | 3 +++
>   2 files changed, 10 insertions(+)

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>

r~
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Patch

diff --git a/target/mips/fpu_helper.h b/target/mips/fpu_helper.h
index 8ca0ca7ea39..6ad1e466cfd 100644
--- a/target/mips/fpu_helper.h
+++ b/target/mips/fpu_helper.h
@@ -47,6 +47,13 @@  static inline void restore_snan_bit_mode(CPUMIPSState *env)
     set_float_infzeronan_rule(izn_rule, &env->active_fpu.fp_status);
     nan3_rule = nan2008 ? float_3nan_prop_s_cab : float_3nan_prop_s_abc;
     set_float_3nan_prop_rule(nan3_rule, &env->active_fpu.fp_status);
+    /*
+     * With nan2008, the default NaN value has the sign bit clear and the
+     * frac msb set; with the older mode, the sign bit is clear, and all
+     * frac bits except the msb are set.
+     */
+    set_float_default_nan_pattern(nan2008 ? 0b01000000 : 0b00111111,
+                                  &env->active_fpu.fp_status);
 
 }
 
diff --git a/target/mips/msa.c b/target/mips/msa.c
index 93a9a87d76d..fc77bfc7b9a 100644
--- a/target/mips/msa.c
+++ b/target/mips/msa.c
@@ -81,4 +81,7 @@  void msa_reset(CPUMIPSState *env)
     /* Inf * 0 + NaN returns the input NaN */
     set_float_infzeronan_rule(float_infzeronan_dnan_never,
                               &env->active_tc.msa_fp_status);
+    /* Default NaN: sign bit clear, frac msb set */
+    set_float_default_nan_pattern(0b01000000,
+                                  &env->active_tc.msa_fp_status);
 }