nx_jpeg_entropy.nx

nx_jpeg_entropy.nx -- baseline-JPEG entropy-coded segment decoder. Per ITU-T Rec. T.81 sec F.2. Heaviest brick of JPEG decode. Per-MCU decode shape (baseline sequential, T.81 sec F.2.1.2): for each color component in the scan: -- DC coefficient (T.81 sec F.2.2.1) T = HUFF_DECODE(DC_table) // 0..15 = "category" DIFF = if T == 0 then 0 else RECEIVE(T) extended via EXTEND(...) DC[0] = prev_dc + DIFF prev_dc = DC[0] -- 63 AC coefficients (T.81 sec F.2.2.2) k = 1 while k < 64: RS = HUFF_DECODE(AC_table) // 8-bit: high4=run, low4=size R = RS >> 4 S = RS & 0x0F if S == 0: if R == 15: k = k + 16 // ZRL (zero-run-length=16) else: k = 64 // EOB (end of block) else: k = k + R // skip R zeros AC[k] = RECEIVE(S) extended via EXTEND(...) k = k + 1 EXTEND(v, T) per T.81 sec F.2.2.1: if v < 2^(T-1) then v - (2^T - 1) else v RECEIVE(T) reads T bits MSB-first from the bitstream. Output: zig-zag-ordered 64-entry coefficient block. Consumer dequantizes + un-zigzags + IDCTs. nx_safety_envelope: intended_use: "Entropy decode for baseline JPEG MCUs." sil_target: SIL1 evidence: [t81_section_f_2_canonical_basis,