ArbitraryBase.js

/**
 * Divide two numbers and get the result of floor division and remainder
 * @param {number} dividend
 * @param {number} divisor
 * @returns {[result: number, remainder: number]}
 */
const floorDiv = (dividend, divisor) => {
 const remainder = dividend % divisor
 const result = Math.floor(dividend / divisor)

 return [result, remainder]
}

/**
 * Converts a string from one base to other. Loses accuracy above the value of `Number.MAX_SAFE_INTEGER`.
 * @param {string} stringInBaseOne String in input base
 * @param {string} baseOneCharacters Character set for the input base
 * @param {string} baseTwoCharacters Character set for the output base
 * @returns {string}
 */
const convertArbitraryBase = (
 stringInBaseOne,
 baseOneCharacterString,
 baseTwoCharacterString
) => {
 if (
 [stringInBaseOne, baseOneCharacterString, baseTwoCharacterString]
 .map((arg) => typeof arg)
 .some((type) => type !== 'string')
 ) {
 throw new TypeError('Only string arguments are allowed')
 }

 const baseOneCharacters = [...baseOneCharacterString]
 const baseTwoCharacters = [...baseTwoCharacterString]

 for (const charactersInBase of [baseOneCharacters, baseTwoCharacters]) {
 if (charactersInBase.length !== new Set(charactersInBase).size) {
 throw new TypeError(
 'Duplicate characters in character set are not allowed'
 )
 }
 }
 const reversedStringOneChars = [...stringInBaseOne].reverse()
 const stringOneBase = baseOneCharacters.length
 let value = 0
 let placeValue = 1
 for (const digit of reversedStringOneChars) {
 const digitNumber = baseOneCharacters.indexOf(digit)
 if (digitNumber === -1) {
 throw new TypeError(`Not a valid character: ${digit}`)
 }
 value += digitNumber * placeValue
 placeValue *= stringOneBase
 }
 const outputChars = []
 const stringTwoBase = baseTwoCharacters.length
 while (value > 0) {
 const [divisionResult, remainder] = floorDiv(value, stringTwoBase)
 outputChars.push(baseTwoCharacters[remainder])
 value = divisionResult
 }
 return outputChars.reverse().join('') || baseTwoCharacters[0]
}

/**
 * Converts a arbitrary-length string from one base to other. Doesn't lose accuracy.
 * @param {string} stringInBaseOne String in input base
 * @param {string} baseOneCharacters Character set for the input base
 * @param {string} baseTwoCharacters Character set for the output base
 * @returns {string}
 */
const convertArbitraryBaseBigIntVersion = (
 stringInBaseOne,
 baseOneCharacterString,
 baseTwoCharacterString
) => {
 if (
 [stringInBaseOne, baseOneCharacterString, baseTwoCharacterString]
 .map((arg) => typeof arg)
 .some((type) => type !== 'string')
 ) {
 throw new TypeError('Only string arguments are allowed')
 }

 const baseOneCharacters = [...baseOneCharacterString]
 const baseTwoCharacters = [...baseTwoCharacterString]

 for (const charactersInBase of [baseOneCharacters, baseTwoCharacters]) {
 if (charactersInBase.length !== new Set(charactersInBase).size) {
 throw new TypeError(
 'Duplicate characters in character set are not allowed'
 )
 }
 }
 const reversedStringOneChars = [...stringInBaseOne].reverse()
 const stringOneBase = BigInt(baseOneCharacters.length)
 let value = 0n
 let placeValue = 1n
 for (const digit of reversedStringOneChars) {
 const digitNumber = BigInt(baseOneCharacters.indexOf(digit))
 if (digitNumber === -1n) {
 throw new TypeError(`Not a valid character: ${digit}`)
 }
 value += digitNumber * placeValue
 placeValue *= stringOneBase
 }
 const outputChars = []
 const stringTwoBase = BigInt(baseTwoCharacters.length)
 while (value > 0n) {
 const divisionResult = value / stringTwoBase
 const remainder = value % stringTwoBase
 outputChars.push(baseTwoCharacters[remainder])
 value = divisionResult
 }
 return outputChars.reverse().join('') || baseTwoCharacters[0]
}

export { convertArbitraryBase, convertArbitraryBaseBigIntVersion }