Re: [FFmpeg-devel] [FFmpeg-cvslog] checkasm: test for abs_pow34

[James Almer <jamrial@gmail.com>]

On 1/23/2024 4:49 PM, Michael Niedermayer wrote:
> On Tue, Jan 23, 2024 at 04:40:46PM -0300, James Almer wrote:
>> On 1/23/2024 4:33 PM, Michael Niedermayer wrote:
>>> On Tue, Jan 23, 2024 at 04:17:22PM -0300, James Almer wrote:
>>>> On 1/23/2024 4:07 PM, Michael Niedermayer wrote:
>>>>> On Mon, Dec 11, 2023 at 04:42:26PM +0000, sunyuechi wrote:
>>>>>> ffmpeg | branch: master | sunyuechi <sunyuechi@iscas.ac.cn> | Tue Nov 28 14:08:12 2023 +0800| [1c3620b2bbe73db9239fcf605e8f535b58f03b86] | committer: Rémi Denis-Courmont
>>>>>>
>>>>>> checkasm: test for abs_pow34
>>>>>>
>>>>>> Signed-off-by: Rémi Denis-Courmont <remi@remlab.net>
>>>>>>
>>>>>>> http://git.videolan.org/gitweb.cgi/ffmpeg.git/?a=commit;h=1c3620b2bbe73db9239fcf605e8f535b58f03b86
>>>>>> ---
>>>>>>
>>>>>>     tests/checkasm/Makefile    |  1 +
>>>>>>     tests/checkasm/aacencdsp.c | 70 ++++++++++++++++++++++++++++++++++++++++++++++
>>>>>>     tests/checkasm/checkasm.c  |  3 ++
>>>>>>     tests/checkasm/checkasm.h  |  1 +
>>>>>>     tests/fate/checkasm.mak    |  3 +-
>>>>>>     5 files changed, 77 insertions(+), 1 deletion(-)
>>>>> [...]
>>>>>> +static void test_abs_pow34(AACEncContext *s) {
>>>>>> +#define BUF_SIZE 1024
>>>>>> +    LOCAL_ALIGNED_32(float, in, [BUF_SIZE]);
>>>>>> +
>>>>>> +    declare_func(void, float *, const float *, int);
>>>>>> +
>>>>>> +    randomize_float(in, BUF_SIZE);
>>>>>> +
>>>>>> +    if (check_func(s->abs_pow34, "abs_pow34")) {
>>>>>> +        LOCAL_ALIGNED_32(float, out, [BUF_SIZE]);
>>>>>> +        LOCAL_ALIGNED_32(float, out2, [BUF_SIZE]);
>>>>>> +
>>>>>> +        call_ref(out, in, BUF_SIZE);
>>>>>> +        call_new(out2, in, BUF_SIZE);
>>>>>> +
>>>>>> +        if (memcmp(out, out2, BUF_SIZE * sizeof(float)) != 0)
>>>>>> +            fail();
>>>>>
>>>>> This is wrong if one of the functions is implemented in C
>>>>> C does not specify float to give bitexact results. Any equality check with
>>>>> float thats expected to end in a reproduceable outcome is generally wrong
>>>>
>>>> Yes, that's why float_near_abs_eps_array() or float_near_ulp_array() should
>>>> be used.
>>>>
>>>>>
>>>>> it also fails in practice
>>>>>
>>>>> TEST    checkasm-aacencdsp
>>>>> Test checkasm-aacencdsp failed. Look at tests/data/fate/checkasm-aacencdsp.err for details.
>>>>> src/tests/Makefile:308: recipe for target 'fate-checkasm-aacencdsp' failed
>>>>> make: *** [fate-checkasm-aacencdsp] Error 1
>>>>>
>>>>> checkasm: using random seed 2523748868
>>>>> SSE:
>>>>>       abs_pow34_sse (aacencdsp.c:55)
>>>>>     - aacencdsp.abs_pow34 [FAILED]
>>>>> checkasm: 1 of 1 tests have failed
>>>>> threads=1
>>>>>
>>>>> thats on plain simple x86-32
>>>>
>>>> Can you check if the following passes for x86-32?
>>>>
>>>>> diff --git a/tests/checkasm/aacencdsp.c b/tests/checkasm/aacencdsp.c
>>>>> index 684c775862..7cc8a01158 100644
>>>>> --- a/tests/checkasm/aacencdsp.c
>>>>> +++ b/tests/checkasm/aacencdsp.c
>>>>> @@ -19,6 +19,7 @@
>>>>>     */
>>>>>
>>>>>    #include <string.h>
>>>>> +#include <float.h>
>>>>>
>>>>>    #include "libavutil/mem.h"
>>>>>    #include "libavutil/mem_internal.h"
>>>>> @@ -51,7 +52,7 @@ static void test_abs_pow34(AACEncContext *s) {
>>>>>            call_ref(out, in, BUF_SIZE);
>>>>>            call_new(out2, in, BUF_SIZE);
>>>>>
>>>>> -        if (memcmp(out, out2, BUF_SIZE * sizeof(float)) != 0)
>>>>> +        if (!float_near_abs_eps_array(out, out2, FLT_EPSILON, BUF_SIZE))
>>>>>                fail();
>>>>>
>>>>>            bench_new(out, in, BUF_SIZE);
>>>>
>>>> That target tends to be pretty picky about the epsilon value because of the
>>>> 80 bits precision for floats.
>>>
>>>
>>> with float.h
>>>
>>> float_near_abs_eps_array
>>>
>>> Test checkasm-aacencdsp failed. Look at tests/data/fate/checkasm-aacencdsp.err for details.
>>> checkasm: using random seed 4097080137
>>> test failed comparing 5.68635 with 5.68635 (abs diff=4.76837e-07 with EPS=1.19209e-07)
>>> SSE:
>>>      abs_pow34_sse (aacencdsp.c:56)
>>>    - aacencdsp.abs_pow34 [FAILED]
>>> checkasm: 1 of 1 tests have failed
>>> threads=1
>>> src/tests/Makefile:317: recipe for target 'fate-checkasm-aacencdsp' failed
>>> make: *** [fate-checkasm-aacencdsp] Error 1
>>>
>>> if (!float_near_abs_eps_array(out, out2, FLT_EPSILON*10, BUF_SIZE))
>>> works but feels wrong
>>>
>>> this works too (only tested 100x on only x86-32 yet)
>>> if (!float_near_ulp_array(out, out2, 1, BUF_SIZE))
>>>
>>> thx
>>
>> 1 is excessive. Some tests use an epsilon value like 0.005, so
>> FLT_EPSILON*10 is IMO fine. Or we could hardcode something like 0.000005
>> instead if it passes.
> 
> 1 ULP is the smallest that works
> tested 100x on mips, arm, mingw32 now too
> 
> epsilon anything is IMHO wrong but iam happy to hear an argument why
> absolute is better than relative here (which is the difference bascially
> IIUC)
> 
> absolute is bad as the difference in what can be represented is relative
> to the values size and so a absolute check will inevitably be very loose
> on small values or will fail on large ones

My bad, didn't notice you suggested float_near_ulp_array() instead of 
float_near_abs_eps_array(), and thought you were suggesting an epsilon 
of 1.0

Should be ok then.
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