Re: [PATCH 04/10] target/tricore: Implement FTOU insn

[Richard Henderson <richard.henderson@linaro.org>]

On 8/27/23 09:36, Bastian Koppelmann wrote:
> On Sun, Aug 27, 2023 at 07:49:52AM -0700, Richard Henderson wrote:
>> On 8/27/23 04:07, Bastian Koppelmann wrote:
>>> On Sat, Aug 26, 2023 at 09:50:51PM -0700, Richard Henderson wrote:
>>>> On 8/26/23 09:02, Bastian Koppelmann wrote:
>>>>> +uint32_t helper_ftou(CPUTriCoreState *env, uint32_t arg)
>>>>> +{
>>>>> +    float32 f_arg = make_float32(arg);
>>>>> +    uint32_t result;
>>>>> +    int32_t flags = 0;
>>>>> +
>>>>> +    if (float32_is_any_nan(f_arg)) {
>>>>> +        result = 0;
>>>>> +        flags |= float_flag_invalid;
>>>>> +    } else if (float32_lt_quiet(f_arg, 0, &env->fp_status)) {
>>>>> +        result = 0;
>>>>> +        flags = float_flag_invalid;
>>>>> +    } else {
>>>>> +        result = float32_to_uint32(f_arg, &env->fp_status);
>>>>> +        flags = f_get_excp_flags(env);
>>>>> +    }
>>>>
>>>> You should allow softfloat to diagnose the special cases, and negative -> 0
>>>> is standard behaviour.  Therefore:
>>>
>>> You're right. However, there is one special case, negative -> 0 ought to raise
>>> float_flags_invalid.
>>
>> https://gitlab.com/qemu-project/qemu/-/blob/master/fpu/softfloat-parts.c.inc?ref_type=heads#L1162
> 
> Lets say the exponent is negative and the sign is negative, then we raise
> float_flag_inexact and we never reach the code you mentioned here. However,
> TriCore HW raises float_flag_invalid as well in that case. This is what I'm
> catching with float32_lt_quiet() in the same manner as ftouz.

Hmph.  Buggy hardware.  You'd better document this special case,
that less-than-zero is detected before rounding.

I presume -0.0 does not raise invalid, that the bug does not extend that far?


r~