K-PKE.Decrypt step 1 (FIPS 203 Alg 15): decode+decompress the ciphertext.
- comp_decomp_sync instance made mode-selectable: Encaps C1/C2 still compress
(mode 0), Decaps ST_DEC_DECOMP decompresses (mode 1) with d=du/dv.
- New ST_DEC_DECOMP state with an inline byteDecode_d walker (reverse of the
C1/C2 bit-packer): walks c_in_bram bytes, accumulates LSB-first into a bit
buffer, extracts d-bit symbols, feeds comp_decomp, writes each decompressed
coeff (mod q) to a bank.
c1 = K polys, d=du -> u'[i] in bank_se rel slot i (0..K-1)
c2 = 1 poly, d=dv -> v' in bank_t rel slot DEC_VSLOT=2 (avoids UPSUM=1)
- dbg_slot_i widened 4->6 bits so the TB can read v' (abs slot 26 at K=4).
- bse/bt write muxes gain the DECOMP writeback paths (dec_u_we / dec_v_we).
Verification: examples/dump_decaps.rs (ml-kem-r worktree) emits per-stage
golden (u'/v'/s_hat/u_hat/w/m') into vectors/decgold/. TB verify_d1 reads back
u'[i] and v' and compares all 256 coeffs each.
Bring-up note: dbg coeff readback latency is bank(1)+dbg_coeff_r(1); the TB's
rdcoeff initially waited 2 cyc and saw data shifted by one index -> fixed to 3.
Verified: dec D1 K=2/3/4 all cases PASS; KeyGen + Encaps unregressed.
FallenSigh
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