Re: [PATCH v2 1/7] target/riscv: Generate nanboxed results from fp helpers

[Richard Henderson]

On 7/23/20 7:35 PM, LIU Zhiwei wrote:
> 
> 
> On 2020/7/24 8:28, Richard Henderson wrote:
>> Make sure that all results from single-precision scalar helpers
>> are properly nan-boxed to 64-bits.
>>
>> Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
>> ---
>>   target/riscv/internals.h  |  5 +++++
>>   target/riscv/fpu_helper.c | 42 +++++++++++++++++++++------------------
>>   2 files changed, 28 insertions(+), 19 deletions(-)
>>
>> diff --git a/target/riscv/internals.h b/target/riscv/internals.h
>> index 37d33820ad..9f4ba7d617 100644
>> --- a/target/riscv/internals.h
>> +++ b/target/riscv/internals.h
>> @@ -38,4 +38,9 @@ target_ulong fclass_d(uint64_t frs1);
>>   #define SEW32 2
>>   #define SEW64 3
>>   +static inline uint64_t nanbox_s(float32 f)
>> +{
>> +    return f | MAKE_64BIT_MASK(32, 32);
>> +}
>> +
> If define it here,  we can also define a more general  function with flen.
> 
> +static inline uint64_t nanbox_s(float32 f, uint32_t flen)
> +{
> +    return f | MAKE_64BIT_MASK(flen, 64 - flen);
> +}
> +
> 
> So we can reuse it in fp16 or bf16 scalar instruction and in vector 
> instructions.

While we could do that, we will not encounter all possible lengths.  In the
cover letter, I mentioned defining a second function,

static inline uint64_t nanbox_h(float16 f)
{
   return f | MAKE_64BIT_MASK(16, 48);
}

Having two separate functions will, I believe, be easier to use in practice.


r~