mathjs/src/utils/bignumber/formatter.js

import { mapObject } from '../object'

/**
 * Convert a BigNumber to a formatted string representation.
 *
 * Syntax:
 *
 *    format(value)
 *    format(value, options)
 *    format(value, precision)
 *    format(value, fn)
 *
 * Where:
 *
 *    {number} value   The value to be formatted
 *    {Object} options An object with formatting options. Available options:
 *                     {string} notation
 *                         Number notation. Choose from:
 *                         'fixed'          Always use regular number notation.
 *                                          For example '123.40' and '14000000'
 *                         'exponential'    Always use exponential notation.
 *                                          For example '1.234e+2' and '1.4e+7'
 *                         'auto' (default) Regular number notation for numbers
 *                                          having an absolute value between
 *                                          `lower` and `upper` bounds, and uses
 *                                          exponential notation elsewhere.
 *                                          Lower bound is included, upper bound
 *                                          is excluded.
 *                                          For example '123.4' and '1.4e7'.
 *                     {number} precision   A number between 0 and 16 to round
 *                                          the digits of the number.
 *                                          In case of notations 'exponential',
 *                                          'engineering', and 'auto',
 *                                          `precision` defines the total
 *                                          number of significant digits returned.
 *                                          In case of notation 'fixed',
 *                                          `precision` defines the number of
 *                                          significant digits after the decimal
 *                                          point.
 *                                          `precision` is undefined by default.
 *                     {number} lowerExp    Exponent determining the lower boundary
 *                                          for formatting a value with an exponent
 *                                          when `notation='auto`.
 *                                          Default value is `-3`.
 *                     {number} upperExp    Exponent determining the upper boundary
 *                                          for formatting a value with an exponent
 *                                          when `notation='auto`.
 *                                          Default value is `5`.
 *    {Function} fn    A custom formatting function. Can be used to override the
 *                     built-in notations. Function `fn` is called with `value` as
 *                     parameter and must return a string. Is useful for example to
 *                     format all values inside a matrix in a particular way.
 *
 * Examples:
 *
 *    format(6.4)                                        // '6.4'
 *    format(1240000)                                    // '1.24e6'
 *    format(1/3)                                        // '0.3333333333333333'
 *    format(1/3, 3)                                     // '0.333'
 *    format(21385, 2)                                   // '21000'
 *    format(12e8, {notation: 'fixed'})                  // returns '1200000000'
 *    format(2.3,    {notation: 'fixed', precision: 4})  // returns '2.3000'
 *    format(52.8,   {notation: 'exponential'})          // returns '5.28e+1'
 *    format(12400,  {notation: 'engineering'})          // returns '12.400e+3'
 *
 * @param {BigNumber} value
 * @param {Object | Function | number} [options]
 * @return {string} str The formatted value
 */
export function format (value, options) {
  if (typeof options === 'function') {
    // handle format(value, fn)
    return options(value)
  }

  // handle special cases
  if (!value.isFinite()) {
    return value.isNaN() ? 'NaN' : (value.gt(0) ? 'Infinity' : '-Infinity')
  }

  // default values for options
  let notation = 'auto'
  let precision

  if (options !== undefined) {
    // determine notation from options
    if (options.notation) {
      notation = options.notation
    }

    // determine precision from options
    if (typeof options === 'number') {
      precision = options
    } else if (options.precision) {
      precision = options.precision
    }
  }

  // handle the various notations
  switch (notation) {
    case 'fixed':
      return toFixed(value, precision)

    case 'exponential':
      return toExponential(value, precision)

    case 'engineering':
      return toEngineering(value, precision)

    case 'auto':
      // TODO: clean up some day. Deprecated since: 2018-01-24
      // @deprecated upper and lower are replaced with upperExp and lowerExp since v4.0.0
      if (options && options.exponential && (options.exponential.lower !== undefined || options.exponential.upper !== undefined)) {
        const fixedOptions = mapObject(options, function (x) { return x })
        fixedOptions.exponential = undefined
        if (options.exponential.lower !== undefined) {
          fixedOptions.lowerExp = Math.round(Math.log(options.exponential.lower) / Math.LN10)
        }
        if (options.exponential.upper !== undefined) {
          fixedOptions.upperExp = Math.round(Math.log(options.exponential.upper) / Math.LN10)
        }

        console.warn('Deprecation warning: Formatting options exponential.lower and exponential.upper ' +
            '(minimum and maximum value) ' +
            'are replaced with exponential.lowerExp and exponential.upperExp ' +
            '(minimum and maximum exponent) since version 4.0.0. ' +
            'Replace ' + JSON.stringify(options) + ' with ' + JSON.stringify(fixedOptions))

        return format(value, fixedOptions)
      }

      // determine lower and upper bound for exponential notation.
      // TODO: implement support for upper and lower to be BigNumbers themselves
      const lowerExp = (options && options.lowerExp !== undefined) ? options.lowerExp : -3
      const upperExp = (options && options.upperExp !== undefined) ? options.upperExp : 5

      // handle special case zero
      if (value.isZero()) return '0'

      // determine whether or not to output exponential notation
      let str
      const rounded = value.toSignificantDigits(precision)
      const exp = rounded.e
      if (exp >= lowerExp && exp < upperExp) {
        // normal number notation
        str = rounded.toFixed()
      } else {
        // exponential notation
        str = toExponential(value, precision)
      }

      // remove trailing zeros after the decimal point
      return str.replace(/((\.\d*?)(0+))($|e)/, function () {
        const digits = arguments[2]
        const e = arguments[4]
        return (digits !== '.') ? digits + e : e
      })

    default:
      throw new Error('Unknown notation "' + notation + '". ' +
          'Choose "auto", "exponential", or "fixed".')
  }
}

/**
 * Format a BigNumber in engineering notation. Like '1.23e+6', '2.3e+0', '3.500e-3'
 * @param {BigNumber | string} value
 * @param {number} [precision]        Optional number of significant figures to return.
 */
export function toEngineering (value, precision) {
  // find nearest lower multiple of 3 for exponent
  const e = value.e
  const newExp = e % 3 === 0 ? e : (e < 0 ? (e - 3) - (e % 3) : e - (e % 3))

  // find difference in exponents, and calculate the value without exponent
  const valueWithoutExp = value.mul(Math.pow(10, -newExp))

  let valueStr = valueWithoutExp.toPrecision(precision)
  if (valueStr.indexOf('e') !== -1) {
    valueStr = valueWithoutExp.toString()
  }

  return valueStr + 'e' + (e >= 0 ? '+' : '') + newExp.toString()
}

/**
 * Format a number in exponential notation. Like '1.23e+5', '2.3e+0', '3.500e-3'
 * @param {BigNumber} value
 * @param {number} [precision]  Number of digits in formatted output.
 *                              If not provided, the maximum available digits
 *                              is used.
 * @returns {string} str
 */
export function toExponential (value, precision) {
  if (precision !== undefined) {
    return value.toExponential(precision - 1) // Note the offset of one
  } else {
    return value.toExponential()
  }
}

/**
 * Format a number with fixed notation.
 * @param {BigNumber} value
 * @param {number} [precision=undefined] Optional number of decimals after the
 *                                       decimal point. Undefined by default.
 */
export function toFixed (value, precision) {
  return value.toFixed(precision)
}