Function ReduceScaleBy

cpp/src/gandiva/decimal_xlarge.cc:167–183

divide input by 10^reduce_by, and round up the fractional part.

// divide input by 10^reduce_by, and round up the fractional part.
static int256_t ReduceScaleBy(int256_t in, int32_t reduce_by) {
  if (reduce_by == 0) {
    // nothing to do.
    return in;
  }

  int256_t divisor = GetScaleMultiplier(reduce_by);
  DCHECK_GT(divisor, 0);
  DCHECK_EQ(divisor % 2, 0);  // multiple of 10.
  auto result = in / divisor;
  auto remainder = in % divisor;
  // round up (same as BasicDecimal128::ReduceScaleBy)
  if (abs(remainder) >= (divisor >> 1)) {
    result += (in > 0 ? 1 : -1);
  }
  return result;
}

// multiply input by 10^increase_by.
static int256_t IncreaseScaleBy(int256_t in, int32_t increase_by) {