Re: [PATCH 05/10] target/tricore: Implement ftohp insn

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

On 8/27/23 00:09, Bastian Koppelmann wrote:
> On Sat, Aug 26, 2023 at 09:55:05PM -0700, Richard Henderson wrote:
>> On 8/26/23 09:02, Bastian Koppelmann wrote:
>>> +uint32_t helper_ftohp(CPUTriCoreState *env, uint32_t arg)
>>> +{
>>> +    float32 f_arg = make_float32(arg);
>>> +    uint32_t result = 0;
>>> +    int32_t flags = 0;
>>> +
>>> +    if (float32_is_infinity(f_arg)) {
>>> +        if (float32_is_neg(f_arg)) {
>>> +            return  HP_NEG_INFINITY;
>>> +        } else {
>>> +            return  HP_POS_INFINITY;
>>> +        }
>>> +    } else if (float32_is_any_nan(f_arg)) {
>>> +        if (float32_is_signaling_nan(f_arg, &env->fp_status)) {
>>> +            flags |= float_flag_invalid;
>>> +        }
>>> +        result = float16_set_sign(result, arg >> 31);
>>> +        result = deposit32(result, 10, 5, 0x1f);
>>> +        result = deposit32(result, 8, 2, extract32(arg, 21, 2));
>>> +        result = deposit32(result, 0, 8, extract32(arg, 0, 8));
>>> +        if (extract32(result, 0, 10) == 0) {
>>> +            result |= (1 << 8);
>>> +        }
>>> +    } else {
>>> +        set_flush_to_zero(0, &env->fp_status);
>>> +        result = float32_to_float16(f_arg, true, &env->fp_status);
>>> +        set_flush_to_zero(1, &env->fp_status);
>>> +        flags = f_get_excp_flags(env);
>>> +    }
>>
>> All of this is standard behaviour.  All you need is the final else case.
> 
> Unfortunately not quite. For NANs the top 2 and lower 8 output mantissa bits need to be
> set to the top 2 and lower 8 input mantissa bits respectively. This behaviour is
> unique to ftohp and hptof, so I don't think we should specialize it in
> parts64_default_nan().

Ah, whereas softfloat grabs the top 10 mantissa bits.
This could use a comment to that effect.

Certainly you don't need to special case infinity though.


r~