Re: [Qemu-devel] [PATCH v1 7/9] tests/tcg: add float_madds test to multiarch

["Alex Bennée" <alex.bennee@linaro.org>]

Richard Henderson <richard.henderson@linaro.org> writes:

> On 9/17/19 2:41 PM, Alex Bennée wrote:
>> +    /* From https://bugs.launchpad.net/qemu/+bug/1841491 */
>> +    add_f32_const(0x1.ffffffffffffcp-1022);
>> +    add_f32_const(0x1.0000000000001p-1);
>> +    add_f32_const(0x0.0000000000001p-1022);
>
> These three constants do not fit in float32.
>
>> +    add_f32_const(0x8p-152);
>> +    add_f32_const(0x8p-152);
>> +    add_f32_const(0x8p-152);
>
> Why are you adding 3 of the same?

To replicate the 1841491 test case where the same number is used for
a/b/c
>
>> +        for (j = 0; j < nums; j++) {
>> +            for (k = 0; k < 3; k++) {
>> +                a = get_f32(j + ((k)%3));
>> +                b = get_f32(j + ((k+1)%3));
>> +                c = get_f32(j + ((k+2)%3));
>
> How does this not overflow nums?
> There does not appear to be an assert on overflow in get_f<N>.

get_f<N> wraps the index with a mod op.

>
>> +#if defined(__arm__)
>> +                r = __builtin_fmaf(a, b, c);
>> +#else
>> +                r = __builtin_fmaf(a, b, c);
>> +#endif
>
> Eh?

Ahh I was going to hardcode the arm madd instruction in as the builtin
wasn't expanding. I tried setting -march in the CFLAGS but that didn't
trigger it either on my buster arm-hf compiler. Any ideas how to get the
compiler to do the right thing?

>
>> +/* Number of constants in each table */
>> +int get_num_f16();
>> +int get_num_f32();
>> +int get_num_f64();
>
> This is not c++; you want (void) to indicate no arguments.

ok.

>
>
> r~


--
Alex Bennée