Function toFixedPoint

src/big-decimal/transcendentals.ts:125–133

* Convert a BigDecimal to a base-2 fixed-point bigint. * * Returns [fp, bits] where fp / 2^bits represents the same value. * `precision` is the requested number of significant *decimal* digits; the * binary grid is sized to hold them with a small guard.

(x: BigDecimal, precision: number)

 * binary grid is sized to hold them with a small guard.
 */
function toFixedPoint(x: BigDecimal, precision: number): [bigint, number] {
  const bits = Math.ceil(precision * LOG2_10) + GUARD_BITS;
  const B = BigInt(bits);
  // value · 2^bits = significand · 10^exponent · 2^bits
  if (x.exponent >= 0) return [(x.significand * pow10(x.exponent)) << B, bits];
  // exponent < 0: divide by 10^(-exponent) after shifting in the binary scale
  // (loses digits below the precision window, as before).
  return [(x.significand << B) / pow10(-x.exponent), bits];
}

/**
 * Convert a base-2 fixed-point bigint (value = fp / 2^bits) back to a