convert_base.js

convert_base.js

function convert_base(input, fromBase, toBase)
{
    const chars = '0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ'

    if (typeof fromBase == 'number') {
        if (fromBase < 2 || fromBase > 62) {
            throw ('Invalid base for from chars, min=2 & max=62')
        }
        fromBase = chars.substr(0, fromBase)
    }

    if (typeof toBase == 'number') {
        if (toBase < 2 || toBase > 62) {
            throw ('Invalid base for to chars, min=2 & max=62')
        }
        toBase = chars.substr(0, toBase)
    }

    input = '' + input
    if (!input || fromBase == toBase) {
        return input
    }

    const [inputLen, fromBaseLen, toBaseLen]
        = [input.length, fromBase.length, toBase.length]

    const numbers = []
    for (var i = 0; i < inputLen; i++) {
        numbers[i] = fromBase.indexOf(input[i])
    }

    var ret = ''
    var oldLen = inputLen

    do {
        var newLen = div = 0

        for (var i = 0; i < oldLen; i++) {
            div = (div * fromBaseLen) + numbers[i]
            if (div >= toBaseLen) {
                numbers[newLen++] = (div / toBaseLen) | 0
                div = div % toBaseLen
            } else if (newLen > 0) {
                numbers[newLen++] = 0
            }
        }

        oldLen = newLen

        ret = (toBase[div] ?? '') + ret
    } while (newLen != 0)

    return ret
}

console.log(convert_base('f8a8d807fa864a679049e0e9e8ab965a', 16, 62))
console.log(convert_base('f8a8d807fa864a679049e0e9e8ab965a', 16, 62) === '7zdg3qSDsAQGNYn94aRvYu')

console.log(convert_base('f8a8d807fa864a679049e0e9e8ab965a', 16, 36))
console.log(convert_base('f8a8d807fa864a679049e0e9e8ab965a', 16, 36) === 'epyqhxglnkss4a7jx2lrjlt96')