Since meson 0.58.0 (released in May 2021), meson accepts adding '.S'
assembly files as source files to the clang-cl compiler.

If using an older version of meson, keep using gas-preprocessor
just like for MSVC builds.

Section 7.9.2 returns 0 "If RefMiRows[ srcIdx ] is not equal to MiRows,
RefMiCols[ srcIdx ] is not equal to MiCols"

dav1d was comparing pixel width/height, not block width/height,
so conform with the spec

Individual OBMC lapped predictions have a max width of 64 pixels
for the top lap and have a max height of 64 for the left laps

This is 7.11.3.9. Overlapped motion compensation process
step4 = Clip3( 2, 16, Num_4x4_Blocks_Wide[ candSz ] )

dav1d wasn't clipping this as needed, which means that with scaled MC, the
interpolation of the 2nd half of a 128 block was incorrect, since mx/my
for subpel filter selection need to be reset at the 64 pixel boundary

This is the parameter combination:
num_y_points == 0 && num_cb_points == 0 && num_cr_points == 0 &&
chroma_scaling_from_luma == 1 && clip_to_restricted_range == 1

Film grain application has two effects: adding noise, and optionally
clipping to video range

For luma, the spec skips film grain application if there's no noise
(num_y_points == 0), but for chroma, it's only skipped if there's no
chroma noise *and* chroma_scaling_from_luma is false

This means it's possible for there to be no noise (num_*_points = 0), but
if clip_to_restricted_range is true then chroma pixels can be clipped to
video range, if chroma_scaling_from_luma is true. Luma pixels, however,
aren't clipped to video range unless there's noise to apply.
dav1d currently skips applying film grain entirely if there is no noise,
regardless of the secondary clipping.

The syntax of itu_t_t35_payload_bytes is not defined in the AV1
specification, but it does state that decoders should ignore the
entire OBU if they do not understand it.

In section 5.11.34 txSz is always defined to TX_4X4 if Lossless is true

Chroma deblock filter size calculation needs to use this overridden txSz
when lossless is enabled

The spec divides err by two, rounding to 0, instead of >>1,
which rounds towards negative infinity

It's possible to encode a large coefficient that becomes 0 after
the clipping in dequant (Abs( dq ) & 0xFFFFFF), e.g. 0x1000000
After that &0xFFFFFF, coeffs are saturated in the range of
[-(1 << (bitdepth+7)), 1 << (bitdepth+7))

dav1d implements this saturation via umin(dq - sign, cf_max), then applies
the sign afterwards via xor. However, for dq = 0 and sign = 1, this step
evaulates to umin(UINT_MAX, cf_max) == cf_max instead of the expected 0.

So instead, do unsigned saturate as umin(dq, cf_max + sign),
then apply sign via (sign ? -dq : dq)
On arm this is the same number of instructions, since cneg exists and is used
On x86 this requires an additional instruction, but this isn't a
latency-critical path

In 8-bit adst, it's possible that the final Round2(x[0], 12) can exceed
16-bits signed

Specifically, in 7.13.2.6. Inverse ADST4 process, the precision requirement is:
"It is a requirement of bitstream conformance that all values stored in the
s and x arrays by this process are representable by a signed integer using
r + 12 bits of precision."

For 8 bits, r is 16 for both row and column, so x[] can be 28-bit signed.
For values [134215680, 134217727] (within 2047 of the maximum 28-bit value),
the final Round2(x[0], 12) evaluates to 32768, exceeding 16-bits signed.

So switch to using sqrshrn, which saturates to 16-bits signed

This is a continuation of: Commit b53ff29d
arm: itx: Do clipping in all narrowing downshifts

Previously, they could be allocated with any random alignment
matching the end of the MuxerContext/DemuxerContext. The
priv structs themselves can have members that require specific
alignment, or at least the default alignment of malloc()/calloc()
(which is sufficient for native types such as uint64_t and
doubles).

This fixes crashes in some arm builds, where GCC (correctly) wants
to use 64 bit aligned stores to write to MD5Context.

Increase the probing size, and change the logic to assume a stream is
valid even if no conclusive decision could be made within the probing
window as long as a sequence header was detected.

Allow checkasm to run.

It is now handled by the gitlab runner.

Ref: 7d859f9c

* Android armv7: target API 19 since it's the lowest directly provided
  by the new NDK.
* Newer NDK has generic tools for ar, strip, etc.
* Remove windres as it's only relevant for Windows targets.

Remove experimental since gcc12, clang14, mold are now in unstable.

Store the used size instead of the allocated size.

The used size can be smaller than the allocated size, which results in
a wrong computation of the linear progress from the frame_progress
bitfield.

The width parameter is used directly as a pointer offset, so ensure
that it has an appropriately sized data type.

This has been done previously for luma, but chroma was overlooked.

Henrik Gramner authored 2 years ago and Henrik Gramner committed 2 years ago

We don't have a separate 8-bit AVX-512 5-tap Wiener filter so the 7-tap
function is used for chroma as well, and in some esoteric edge cases
chroma dst pointers may only have a 32-byte alignment despite having
a width larger than 32, so use an unaligned store as a workaround.

The pattern matching feature has been improved and is now performed
under the new --function parameter, rendering this one obsolete.

Allows to run checkasm only for functions matching a given pattern.

The copy_lpf_progress bitfield might not be fully cleared when size goes
down.

Credit to Oss-Fuzz.

Fixes a regression since commit 3d3c51a0.

The code size increase of inlining every call to certain functions
isn't a worthwhile trade-off, and most compilers actually ends up
overriding those particular inlining hints anyway.

In some cases it's also better to split the function into separate
luma and chroma functions.

Henrik Gramner authored 2 years ago and Henrik Gramner committed 2 years ago

In 0aca76c3 sequences of pand/pandn/por was replaced by pblendvb, but
one instruction (which now acts as a no-op) was accidentally left in.

The NEON loop filter's innermost asm function can return to a different
location than the address that called it. This messes up the return stack
predictor, causing returns to be mispredicted

Instead, rework the function to always return to the address that calls it,
and instead return the information needed for the caller to short-circuit
storing pixels

Konstantin Pavlov authored 2 years ago and Henrik Gramner committed 2 years ago

snapcraft version we use is no longer compatible with authentication
schemes snap store uses.  This could be fixed by updating the snapcraft
inside the docker image, but Ubuntu no longer ships an up to date
snapcraft version in their own repositories.  The other way to install
snapcraft is to manually fetch the project and core snaps just like we
do in https://code.videolan.org/videolan/docker-images/-/blob/master/vlc-ubuntu-focal/Dockerfile,
but that currently fails on Jammy due to conflict in Python versions
between what is shipped in Jammy and inside snapcraft project.

All in all, it seems snapcraft seems to be abandoned for our CI
use-case, and the usefulness of dav1d snap is disputable, so just drop
it altogether.  Packaging is still available in package/snap/ for the
brave souls who want to build it on their own.

Henrik Gramner authored 2 years ago and Henrik Gramner committed 2 years ago

When compiling with asm enabled there's no point in compiling
C versions of DSP functions that have asm implementations using
instruction sets that the compiler can unconditionally use.

E.g. when compiling with -mssse3 we can remove the C version
of all functions with SSSE3 implementations.

This is accomplished using the compiler's dead code elimination
functionality.

Can be configured using the new 'trim_dsp' meson option, which
by default is enabled when compiling in release mode.

Enabling/disabling signal handlers is very slow and requires a syscall.

A better approach is to keep the signal handlers enabled all the time,
and use a simple flag variable to determine if a given signal should
be handled or passed on to the default signal handler.

GetTickCount() increases at a very low frequency, >10ms per tick.
When running multiple loops of checkasm instances in parallel
different instances regularly ends up using identical seeds.

Prefer the use of QueryPerformanceCounter() instead, which ticks at
a significantly higher rate, which in turn increases randomness.