bignumber.js 去尾/进一 保留n位小数方式

import BigNumber from "bignumber.js"
export function bigNumberFloor(num: string|number|BigNumber, decimals: number): string {
  return new BigNumber(num).times(10**decimals).idiv(1).div(10**decimals).toFormat()
}
export function bigNumberCeil(num: string|number|BigNumber, decimals: number): BigNumber {
  return new BigNumber(num).times(10**decimals).integerValue(BigNumber.ROUND_CEIL).div(10**decimals)
}