Substitutes H264DSPContext.chroma_dc_dequant_idct in the 4:2:0 /
bit_depth=8 init path with a wrapper that composes the daedalus
chroma DC Hadamard primitive (daedalus-fourier PR #25) with the
qmul scaling FFmpeg's reference does in one fused function
(h264idct_template.c::ff_h264_chroma_dc_dequant_idct).
Algorithm per H.264 §8.5.11.1 / §8.5.11.2:
1. Extract 4 DCs from the scattered positions in the per-MB
coefficient buffer (stride=32, xStride=16)
2. 2x2 Hadamard transform (daedalus primitive)
3. qmul scale + >> 7, write back to original positions
Bit-exact against ff_h264_chroma_dc_dequant_idct_8_c. The Hadamard
itself is gated by the fourier PR #23 7-case test suite (including
the H·H = 4·I algebraic invariant), and the public-API parity
test added in PR #25 confirms the src/ symbol matches the test ref.
4:2:2 chroma stays on the in-tree ff_h264_chroma422_dc_dequant_idct_c
path — same chroma_format_idc<=1 gating shape as 0009 chroma deblock.
Pin bump: _daedalus_fourier_commit / DAEDALUS_FOURIER_COMMIT bumped
to b9f9ff2a (post-PR #25) so the build picks up the public
daedalus_h264_chroma_dc_hadamard_2x2 symbol.
Verified the patch applies cleanly on top of 0001-0010 against the
pinned upstream commit b57fbbe5 on hertz.
claude-noether
d8aa3aae8d