FFmpeg

mirror of https://mirror.skon.top/https://github.com/FFmpeg/FFmpeg synced 2026-04-20 21:00:41 +08:00

Files

Andreas Rheinhardt 581050a175 tests/checkasm: Add mpegvideo unquantize test

This adds a test for the mpegvideo unquantize functions.

It has been written in order to be able to easily bench
these functions. It should be noted that the random input
fed to the tested functions is not necessarily representative
of the stuff actually occuring in the wild. So benchmarks should
be taken with a grain of salt; but comparisons between two functions
that do not depend on branch predictions are valid (the usecase
for this is to port the x86 mmx functions to use xmm registers).

During testing I have found a bug in the arm/aarch64 neon optimizations
when using the LIBMPEG2 permutation (used by FF_IDCT_INT): The code
seems to be based on the presumption that the remainder of the number
of coefficients to process is always <= 4 mod 16. The test therefore
sometimes fails for these arches.

Hint: I am not certain that 16 bits are enough for the intermediate
values of all the computations involved; e.g. both FLV and MPEG-4
escape values can go beyond that after the corresponding
multiplications. The input in this test is nevertheless designed
to fit into 16 bits.

Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>

2025-12-03 10:23:39 +01:00