Re: [Qemu-devel] [PATCH v2 2/5] target-tricore: Added MADD.F and MSUB.F instructions

[Bastian Koppelmann]

On 11/08/2016 12:42 PM, Richard Henderson wrote:
> On 11/07/2016 03:44 PM, Bastian Koppelmann wrote:
>> Multiplies D[a] and D[b] and adds/subtracts the result to/from D[d].
>> The result is put in D[c]. All operands are floating-point numbers.
>>
>> Signed-off-by: Bastian Koppelmann <address@hidden>
>> ---
>>  target-tricore/fpu_helper.c | 93
>> ++++++++++++++++++++++++++++++++++++++++++++-
>>  target-tricore/helper.h     |  2 +
>>  target-tricore/translate.c  |  8 ++++
>>  3 files changed, 102 insertions(+), 1 deletion(-)
>>
>> diff --git a/target-tricore/fpu_helper.c b/target-tricore/fpu_helper.c
>> index f717b53..d530a0b 100644
>> --- a/target-tricore/fpu_helper.c
>> +++ b/target-tricore/fpu_helper.c
>> @@ -21,7 +21,8 @@
>>  #include "cpu.h"
>>  #include "exec/helper-proto.h"
>>
>> -#define ADD_NAN   0x7cf00001
>> +#define QUIET_NAN 0x7fc00000
>> +#define ADD_NAN   0x7fc00001
>>  #define DIV_NAN   0x7fc00008
>>  #define MUL_NAN   0x7fc00002
>>  #define FPU_FS PSW_USB_C
>> @@ -47,6 +48,42 @@ static inline bool f_is_denormal(float32 arg)
>>      return float32_is_zero_or_denormal(arg) && !float32_is_zero(arg);
>>  }
>>
>> +static inline float32 f_maddsub_nan_result(float32 arg1, float32 arg2,
>> +                                           float32 arg3, float32 result,
>> +                                           uint32_t flags)
>> +{
>> +    uint32_t aSign, bSign, cSign;
>> +    uint32_t aExp, bExp, cExp;
>> +
>> +    if (float32_is_any_nan(arg1) || float32_is_any_nan(arg2) ||
>> +        float32_is_any_nan(arg3)) {
>> +        return QUIET_NAN;
>> +    } else if (float32_is_infinity(arg1) && float32_is_zero(arg2)) {
>> +        return MUL_NAN;
>> +    } else if (float32_is_zero(arg1) && float32_is_infinity(arg2)) {
>> +        return MUL_NAN;
>> +    } else {
>> +        aSign = arg1 >> 31;
>> +        bSign = arg2 >> 31;
>> +        cSign = arg3 >> 31;
>> +
>> +        aExp = (arg1 >> 23) & 0xff;
>> +        bExp = (arg2 >> 23) & 0xff;
>> +        cExp = (arg3 >> 23) & 0xff;
>> +
>> +        if (flags & float_muladd_negate_c) {
> 
> flags here is muladd argument,
> 

I don't know what you mean by that.

However, I took this from softfloat's float32_muladd() to catch the case
of an invalid addition to return the correct NAN.

I thought of extending softfloat's muladd() to return a specializable
ADD_NAN to catch this case in the first place, but TriCore would be the
only target using it and I'm not sure if it's worth while.

Any comments on this idea?

Cheers,
    Bastian