Function divideWithPrecision

repos/effect/packages/effect/src/BigDecimal.ts:472–521

(
  num: bigint,
  den: bigint,
  scale: number,
  precision: number
)

  precision: number
): BigDecimal => {
  const numNegative = num < bigint0
  const denNegative = den < bigint0
  const negateResult = numNegative !== denNegative

  num = numNegative ? -num : num
  den = denNegative ? -den : den

  // Shift digits until numerator is larger than denominator (set scale appropriately).
  while (num < den) {
    num *= bigint10
    scale++
  }

  // First division.
  let quotient = num / den
  let remainder = num % den

  if (remainder === bigint0) {
    // No remainder, return immediately.
    return make(negateResult ? -quotient : quotient, scale)
  }

  // The quotient is guaranteed to be non-negative at this point. No need to consider sign.
  let count = `${quotient}`.length

  // Shift the remainder by 1 decimal; The quotient will be 1 digit upon next division.
  remainder *= bigint10
  while (remainder !== bigint0 && count < precision) {
    const q = remainder / den
    const r = remainder % den
    quotient = quotient * bigint10 + q
    remainder = r * bigint10

    count++
    scale++
  }

  if (remainder !== bigint0) {
    // Round final number with remainder.
    quotient += roundTerminal(remainder / den)
  }

  return make(negateResult ? -quotient : quotient, scale)
}

/**
 * Internal function used for rounding.
 *
 * Returns 1 if the most significant digit is >= 5, otherwise 0.
 *
 * This is used after dividing a number by a power of ten and rounding the last digit.
 *
 * @internal