Function bitLength

src/big-decimal/utils.ts:47–62

(n: bigint)

/** Bit length of |n| (the number of bits in its binary representation). */
export function bitLength(n: bigint): number {
  if (n < 0n) n = -n;
  if (n === 0n) return 0;
  let bits = 0;
  // Doubling search to bracket the bit length.
  let high = 1;
  while (n >> BigInt(high) > 0n) high *= 2;
  // Binary search within [0, high].
  for (let shift = high >> 1; shift >= 1; shift >>= 1) {
    if (n >> BigInt(shift) > 0n) {
      bits += shift;
      n >>= BigInt(shift);
    }
  }
  return bits + 1;
}

/** Fixed-point multiply on the base-2 grid: (a * b) >> bits */
export function fpmul(a: bigint, b: bigint, bits: number): bigint {