nx_logadd_lib.nx

nx_logadd_lib.nx -- FIXED-POINT LOG-DOMAIN ARITHMETIC, no floats anywhere: the primitive a linear-chain CRF's forward-backward pass needs (log-sum-exp) and the probability it reads back (exp of a non-positive log-domain value). Scale LA_S = 1024 units per nat (Q10). la_lse(a, b) = ln(e^a + e^b) in Q10; la_exp_neg(x), x <= 0 -> a Q10 probability. The two tables are built ONCE from first principles rather than typed: e^(-1/S) in Q30 from its Taylor series (the third term is already below one unit at this scale, so the constant is exact to the last bit), the powers e^(-d/S) by recurrence, and softplus(d) = S*ln(1 + e^(-d/S)) through the estate's ONE integer logarithm (nx_intlog ilog2_1024) -- composed, never re-implemented. The horizon LA past which softplus rounds to zero is DERIVED at init by scanning the table, never declared. Minus infinity is LA_NEG_INF, the same sentinel the aspect model's Viterbi already uses, so a masked transition reads identically in both decoders. license_tier: ORIGINAL No hw writes (Rule 26). LIB.