nx_bond_lib.nx

nx_bond_lib.nx -- FIXED-INCOME VALUATION: bond price, yield-to-maturity, duration. Integer-exact. The fixed-income companion to nx_dcf_lib (equity intrinsic value). A bond is a stream of coupons plus a face repayment; its PRICE is the present value of that stream at a discount yield, and its YIELD-TO-MATURITY is the inverse -- the single rate that makes the PV equal the market price. Together, DCF (equities) + this (bonds) value both sides of a real portfolio. NO FLOATS. The discount factor is carried scaled x1e6 and rolled forward one period at a time (df_t = df_{t-1} * 10000 / (10000 + ytm_bp)); every present value is exact integer arithmetic with defined downward truncation, identical to nx_dcf_lib. Coupons and yields are basis points (10% -> 1000). *YTM BY INTEGER BISECTION, NOT NEWTON-RAPHSON. Price is strictly monotone-decreasing in yield, so a bisection on basis points is exact and cannot diverge -- unlike the float Newton step every mainstream library uses, which can oscillate or shoot to a garbage root on a bad initial guess. And it is FAIL-CLOSED: a target price above the zero-yield maximum (would require a negative yield) or below the max-search-yield floor is REFUSED (BOND_NO_CONVERGE) rather than returning an invented number. A yield you cannot bracket honestly is not a yield. SCALE ENVELOPE (declared): face*coupon_bp and cf*df fit i64 for face up to ~9e8 minor units at bp<=1e5. bisection is O(log(YTM_MAX) * periods). Self-contained (no imports); the df identity is shared with nx_dcf_lib by design, not by copy of a service. license_tier: ORIGINAL No hw writes (Rule 26). LIB.