nx_jpeg_mcu.nx

nx_jpeg_mcu.nx -- baseline-JPEG MCU walker. Per ITU-T Rec. T.81 sec A.2.3. The top-level orchestrator that ties together every per-block primitive shipped earlier in Arc C1. MCU = Minimum Coded Unit. For each MCU position in the image: for each component (in scan order): for each data unit (block) in this MCU for this component: (Hi * Vi blocks total for component i) 1. nx_jpeg_ent_decode_block -- entropy decode -> zz-order 64 coeffs 2. nx_jpeg_dequant_un_zigzag -- * QTable, un-zigzag -> 64 nat coeffs 3. nx_jpeg_idct_8x8 -- inverse DCT -> 64 samples 4. level shift +128 + clamp to [0..255] -> 64 u8 samples 5. write to component sample plane at correct (x,y) Per-component plane dimensions (T.81 sec A.2.4): x_i = ceil(X * Hi / max_h) y_i = ceil(Y * Vi / max_v) For 4:2:0 YCbCr (max_h = max_v = 2; Y has H=V=2, Cb/Cr H=V=1): Y plane: full image width x height (each MCU contributes 16x16 px = 4 blocks) Cb plane: half width x half height (each MCU contributes 8x8 px = 1 block) Cr plane: half width x half height (each MCU contributes 8x8 px = 1 block) nx_safety_envelope: intended_use: "Top-level MCU walker for baseline JPEG decode." sil_target: SIL1 evidence: [t81_section_a_2_3_canonical_basis, composes_9_per_block_primitives, bounded_iteration_via_sof_mcu_rows_cols] hazard_register: [bug-tape-mcu-grid-overrun, bug-tape-component-plane-stride-mismatch, bug-tape-prev-dc-not-reset-per-scan] residual_risk: "Restart-marker (DRI) interval handling not yet wired -- baseline JPEGs without restart markers decode correctly; those with RST0..RST7 markers need a follow-on stone." verdict: NOT_YET_EVALUATED