Re: [Qemu-devel] [PATCH v2 1/5] target-tricore: Added FTOUZ instruction

[Bastian Koppelmann <kbastian@mail.uni-paderborn.de>]

On 11/08/2016 12:36 PM, Richard Henderson wrote:
> On 11/07/2016 03:44 PM, Bastian Koppelmann wrote:
>> Converts a 32-bit floating point number to an unsigned int. The
>> result is rounded towards zero.
>>
>> Signed-off-by: Bastian Koppelmann <kbastian@mail.uni-paderborn.de>
>> ---
>> v1 -> v2:
>>     - ftouz: Correctly convert the result from uint32 to f32
>>
>>  target-tricore/fpu_helper.c | 43
>> +++++++++++++++++++++++++++++++++++++++++++
>>  target-tricore/helper.h     |  1 +
>>  target-tricore/translate.c  |  3 +++
>>  3 files changed, 47 insertions(+)
>>
>> diff --git a/target-tricore/fpu_helper.c b/target-tricore/fpu_helper.c
>> index 98fe947..f717b53 100644
>> --- a/target-tricore/fpu_helper.c
>> +++ b/target-tricore/fpu_helper.c
>> @@ -215,3 +215,46 @@ uint32_t helper_itof(CPUTriCoreState *env,
>> uint32_t arg)
>>      }
>>      return (uint32_t)f_result;
>>  }
>> +
>> +uint32_t helper_ftouz(CPUTriCoreState *env, uint32_t arg)
>> +{
>> +    float32 f_arg = make_float32(arg);
>> +    uint32_t result;
>> +    int32_t flags;
>> +    result = float32_to_uint32_round_to_zero(f_arg, &env->fp_status);
>> +
>> +    flags = f_get_excp_flags(env);
>> +    if (flags) {
>> +        if (float32_is_any_nan(f_arg)) {
>> +            flags |= float_flag_invalid;
>> +            result = 0;
>> +        /* f_real(D[a]) < 0.0 */
>> +        } else if (float32_lt_quiet(f_arg, 0.0, &env->fp_status)) {
>> +            flags |= float_flag_invalid;
>> +            result = 0;
>> +        /* f_real(D[a]) > 2^32 -1  */
>> +        } else if (float32_lt_quiet(0x4f800000, f_arg,
>> &env->fp_status)) {
>> +            flags |= float_flag_invalid;
>> +            result = 0xffffffff;
>> +        } else {
>> +            flags &= ~float_flag_invalid;
>> +        }
> 
> I don't understand this bit.  Surely float_flag_invalid is already set
> by softfloat.  And the bounding is done as well.  What's up?
> 

Consider 0x836d4e86 as an input which is clearly negative, however
float_flag_invalid is not set. The hardware on the other hand does set it.

Cheers,
    Bastian