phase1: substrate selector API + cross-substrate bit-exact ctest #9
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Reference: marfrit/daedalus-decoder#9
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Surfaces daedalus-fourier's substrate-override at the decoder boundary: new
daedalus_decoder_set_substrate(dec, AUTO/CPU/QPU)setter with the same mid-frame restriction as set_output_format. Default unchanged (AUTO).New ctest
idct_bitexact_cpure-runs QVGA forcing the NEON path; produces byte-identical output to the AUTO/QPU run, confirming the V3D shaders and daedalus-fourier's CPU reference agree at the spec level. Also unlocks the bit-exact suite on hosts without V3D7 (CI runners, x86).Surfaces daedalus-fourier's substrate-override capability at the decoder boundary. Lets tests run on CPU-only hosts (CI runners, x86 dev boxes) AND cross-checks V3D shader output against NEON reference on hosts that have both. API additions (pre-0.1 ABI, additive): - daedalus_decoder_substrate enum { AUTO, CPU, QPU } (mirrors daedalus_substrate; isolated for ABI reasons). - daedalus_decoder_set_substrate(dec, sub) setter, same mid-frame-change restrictions as set_output_format. - Default remains AUTO — the only sensible choice for production. Internal: - flush_frame now calls daedalus_dispatch_h264_idct{4,8} with an explicit substrate instead of daedalus_recipe_dispatch_*. Mapped via a small map_substrate() helper. No perf delta on AUTO (recipe layer was just doing the same dispatch under the hood). Test changes: - test_smoke: new EXPECTs for set_substrate (valid + bogus). - test_idct_bitexact: new argv[4] takes "auto" (default), "cpu", or "qpu" to force the substrate. - CMakeLists.txt: new ctest entry `idct_bitexact_cpu` re-runs the QVGA case forcing the CPU path. Catches silent drift between the V3D shader and the NEON reference; both must produce identical output for the same coefficient input (and they do — see ctest log below). Verified on hertz (Pi 5 / V3D 7.1 / daedalus-fourier 0.1.0): $ ctest --test-dir build --output-on-failure Start 1: smoke 1/4 Test #1: smoke ............................ Passed 0.10 sec Start 2: idct_bitexact 2/4 Test #2: idct_bitexact .................... Passed 0.03 sec Start 3: idct_bitexact_cpu 3/4 Test #3: idct_bitexact_cpu ................ Passed 0.03 sec Start 4: idct_bitexact_1080p 4/4 Test #4: idct_bitexact_1080p .............. Passed 0.06 sec 100% tests passed, 0 tests failed out of 4 CPU substrate produces byte-identical Y + Cb + Cr planes against the same C reference that the AUTO/QPU path matches — confirming the V3D shaders and the daedalus-fourier NEON path agree at the spec level. Why we plumbed the lower-level dispatch instead of leaving recipe in place: recipe is just a thin wrapper that calls dispatch with AUTO. Once we needed substrate control, the wrapper became a liability (would have required adding a parallel recipe API for each substrate); going direct is simpler and the AUTO path is unchanged. Coverage note: idct_bitexact_cpu runs at QVGA (300 MBs); not also at 1080p because the CPU path's wall time scales linearly with block count and a 1080p CPU run is ~0.5s on hertz — fine standalone but slows ctest enough that it would tempt opt-in gating. The bit-exact content is the same regardless of frame size; the 1080p variant only exists to gate index-arithmetic bugs that surface above small int boundaries.