BN <-> Decimal String

decimalString.test.ts

test("decimalStringFromBN", () => {
  expect(types.decimalStringFromBN(new BN(0))).toEqual("0");
  expect(types.decimalStringFromBN(new BN(0), 1)).toEqual("0");
  expect(types.decimalStringFromBN(new BN(1000000))).toEqual("1000000");
  expect(types.decimalStringFromBN(new BN(1000000), 1)).toEqual("100000");
  expect(types.decimalStringFromBN(new BN(1000001), 1)).toEqual("100000.1");
  expect(types.decimalStringFromBN(new BN(1000100), 1)).toEqual("100010");
  expect(types.decimalStringFromBN(new BN(1000000), 2)).toEqual("10000");
  expect(types.decimalStringFromBN(new BN(1000001), 2)).toEqual("10000.01");
  expect(types.decimalStringFromBN(new BN(1000100), 2)).toEqual("10001");
  expect(types.decimalStringFromBN(new BN(1000000), 5)).toEqual("10");
  expect(types.decimalStringFromBN(new BN(1000001), 5)).toEqual("10.00001");
  expect(types.decimalStringFromBN(new BN(1000100), 5)).toEqual("10.001");
  expect(types.decimalStringFromBN(new BN(1000000), 6)).toEqual("1");
  expect(types.decimalStringFromBN(new BN(1000001), 6)).toEqual("1.000001");
  expect(types.decimalStringFromBN(new BN(1000100), 6)).toEqual("1.0001");
  expect(types.decimalStringFromBN(new BN(1000000), 7)).toEqual("0.1");
  expect(types.decimalStringFromBN(new BN(1000001), 7)).toEqual("0.1000001");
  expect(types.decimalStringFromBN(new BN(1000100), 7)).toEqual("0.10001");
  expect(types.decimalStringFromBN(new BN(1000000), 8)).toEqual("0.01");
  expect(types.decimalStringFromBN(new BN(1000001), 8)).toEqual("0.01000001");
  expect(types.decimalStringFromBN(new BN(1000100), 8)).toEqual("0.010001");
  expect(types.decimalStringFromBN(new BN(1000000), 10)).toEqual("0.0001");
  expect(types.decimalStringFromBN(new BN(1000001), 10)).toEqual(
    "0.0001000001"
  );
  expect(types.decimalStringFromBN(new BN(1000100), 10)).toEqual("0.00010001");
  expect(types.decimalStringFromBN(new BN("3141592653589793238"), 18)).toEqual(
    "3.141592653589793238"
  );

  expect(() => types.decimalStringFromBN(new BN(-1))).toThrow();
});

test("bnFromDecimalString", () => {
  expect(types.bnFromDecimalString("0")).toEqual(new BN(0));
  expect(types.bnFromDecimalString("0", 1)).toEqual(new BN(0));
  expect(types.bnFromDecimalString("1000000")).toEqual(new BN(1000000));
  expect(types.bnFromDecimalString("100000", 1)).toEqual(new BN(1000000));
  expect(types.bnFromDecimalString("100000.1", 1)).toEqual(new BN(1000001));
  expect(types.bnFromDecimalString("100010", 1)).toEqual(new BN(1000100));
  expect(types.bnFromDecimalString("10000", 2)).toEqual(new BN(1000000));
  expect(types.bnFromDecimalString("10000.01", 2)).toEqual(new BN(1000001));
  expect(types.bnFromDecimalString("10001", 2)).toEqual(new BN(1000100));
  expect(types.bnFromDecimalString("10", 5)).toEqual(new BN(1000000));
  expect(types.bnFromDecimalString("10.00001", 5)).toEqual(new BN(1000001));
  expect(types.bnFromDecimalString("10.001", 5)).toEqual(new BN(1000100));
  expect(types.bnFromDecimalString("1", 6)).toEqual(new BN(1000000));
  expect(types.bnFromDecimalString("1.000001", 6)).toEqual(new BN(1000001));
  expect(types.bnFromDecimalString("1.0001", 6)).toEqual(new BN(1000100));
  expect(types.bnFromDecimalString("0.1", 7)).toEqual(new BN(1000000));
  expect(types.bnFromDecimalString("0.1000001", 7)).toEqual(new BN(1000001));
  expect(types.bnFromDecimalString("0.10001", 7)).toEqual(new BN(1000100));
  expect(types.bnFromDecimalString("0.01", 8)).toEqual(new BN(1000000));
  expect(types.bnFromDecimalString("0.01000001", 8)).toEqual(new BN(1000001));
  expect(types.bnFromDecimalString("0.010001", 8)).toEqual(new BN(1000100));
  expect(types.bnFromDecimalString("0.0001", 10)).toEqual(new BN(1000000));
  expect(types.bnFromDecimalString("0.0001000001", 10)).toEqual(
    new BN(1000001)
  );
  expect(types.bnFromDecimalString("0.00010001", 10)).toEqual(new BN(1000100));
  expect(types.bnFromDecimalString("3.141592653589793238", 18)).toEqual(
    new BN("3141592653589793238")
  );

  expect(types.bnFromDecimalString(".", 1)).toEqual(new BN(0));
  expect(types.bnFromDecimalString("1.", 1)).toEqual(new BN(10));
  expect(types.bnFromDecimalString(".1", 1)).toEqual(new BN(1));
  expect(types.bnFromDecimalString(".1", 2)).toEqual(new BN(10));
  expect(types.bnFromDecimalString(".10", 2)).toEqual(new BN(10));
  expect(types.bnFromDecimalString("1.", 2)).toEqual(new BN(100));

  expect(types.bnFromDecimalString("3.14159265", 2)).toEqual(new BN(314));

  expect(() => types.bnFromDecimalString("-1")).toThrow();
});

decimalString.ts

/**
 * @license
 * Copyright (c) 2020 petejkim
 * SPDX-License-Identifier: MIT
 */

/**
 * Convert a BN object to a string representation of a positive decimal number
 * @param bn BN object
 * @param decimalPlaces Number of decimal places
 * @returns String representation of a positive decimal number
 */
export function decimalStringFromBN(bn: BN, decimalPlaces = 0): string {
  if (bn.isNeg()) {
    throw new Error("Number must be positive");
  }
  if (bn.isZero()) {
    return "0";
  }
  let str = bn.toString(10).padStart(decimalPlaces + 1, "0");
  if (decimalPlaces === 0) {
    return str;
  }
  str = str.slice(0, -decimalPlaces) + "." + str.slice(-decimalPlaces);
  str = str.replace(/\.0+$/, "");
  if (str.includes(".")) {
    str = str.replace(/0+$/, "");
  }
  return str;
}

/**
 * Convert a string representation of a positive decimal number to BN object
 * @param decimalNumber String representation of a positive decimal number
 * @param decimalPlaces Number of decimal places
 * @returns BN object
 * @throws Error
 */
export function bnFromDecimalString(
  decimalNumber: string,
  decimalPlaces = 0
): BN {
  if (decimalNumber.startsWith("-")) {
    throw new Error("Number must be positive");
  }
  if (!decimalNumber || !/^\d*(\.\d*)?$/.test(decimalNumber)) {
    throw new Error("Invalid string representation of a decimal number");
  }
  let [whole, fractional] = decimalNumber.split(".");
  whole = whole || "0";
  fractional = (fractional || "0")
    .slice(0, decimalPlaces)
    .padEnd(decimalPlaces, "0");

  return new BN(whole + fractional, 10);
}