Function fpln

src/big-decimal/utils.ts:351–362

(x: bigint, bits: number)

const LN_AGM_MIN_BITS = 40000; // ≈ 12040 decimal digits

export function fpln(x: bigint, bits: number): bigint {
  const scale = 1n << BigInt(bits);
  // Defense in depth: a non-positive input is a caller bug (callers
  // range-reduce so the kernel only sees O(1) positive values). A zero
  // input used to hang forever in the sqrt-reduction loop (fpsqrt(0) = 0).
  if (x <= 0n) throw new RangeError('fpln: input must be positive');

  // ln(1) = 0
  if (x === scale) return 0n;

  return bits >= LN_AGM_MIN_BITS ? fplnAGM(x, bits) : fplnDirect(x, bits);
}

/**
 * Direct-log fixed-point natural logarithm (machine-seed + log1p correction).