dav1d 1.5.4 Brings AV1 Decoding To OS/2

While the VideoLAN developers are busy these days working on dav2d for AV2 video decoding, they haven't let up work on dav1d and recently released dav1d 1.5.4 for continuing to enhance this leading open-source, CPU-based AV1 decoder.

With dav1d 1.5.4 they have introduced support foir OS/2. Dav1d to the OS/2 operating system ended up being a fairly easy port with just Meson build system and header file changes.

Dav1d 1.5.4 also adds Armv9.3-A Guarded Control Stack "GCS" support, AArch64 optimizations, RISC-V optimizations, portability improvements for non-POSIX systems, and other updates.

- Support for OS/2, including API exports and assembly
- Switch to external checkasm
- Add Armv9.3-A GCS (Guarded Control Stack) support
- AArch64: optimize ipred_v, ipred_h and ipred_smooth_* 8bpc functions, and reduce .text size
- ARM32: optimize prep_neon
- RISC-V: ipred_(dc, h, v, pal) optimizations for 8 and 16bpc, generate_grain_y for 8bpc, and optimizations (prep/put_8tap, 6-tap and copy paths)
- Portability improvements for non-POSIX systems (signal() fallback)
- Schedule tile tasks for all passes at once, improving threading
- Precompute the quantization matrix tables at build time
- Move loop-invariant computations out of hot loops

Dav1d 1.5.4 can be downloaded at VideoLAN.org.