def convert_hexstr_to_bigbase(hexstr, alphabet=ALPHABET, bigbase=BIGBASE):
    r"""
    Packs a long hexstr into a shorter length string with a larger base

    Ignore:
        # Determine the length savings with lossless conversion
        import sympy as sy
        consts = dict(hexbase=16, hexlen=256, bigbase=27)
        symbols = sy.symbols('hexbase, hexlen, bigbase, newlen')
        haexbase, hexlen, bigbase, newlen = symbols
        eqn = sy.Eq(16 ** hexlen,  bigbase ** newlen)
        newlen_ans = sy.solve(eqn, newlen)[0].subs(consts).evalf()
        print('newlen_ans = %r' % (newlen_ans,))

        # for a 27 char alphabet we can get 216
        print('Required length for lossless conversion len2 = %r' % (len2,))

        def info(base, len):
            bits = base ** len
            print('base = %r' % (base,))
            print('len = %r' % (len,))
            print('bits = %r' % (bits,))
        info(16, 256)
        info(27, 16)
        info(27, 64)
        info(27, 216)
    """
    x = int(hexstr, 16)  # first convert to base 16
    if x == 0:
        return '0'
    sign = 1 if x > 0 else -1
    x *= sign
    digits = []
    while x:
        digits.append(alphabet[x % bigbase])
        x //= bigbase
    if sign < 0:
        digits.append('-')
        digits.reverse()
    newbase_str = ''.join(digits)
    return newbase_str
r"""
    Packs a long hexstr into a shorter length string with a larger base

    Ignore:
        # Determine the length savings with lossless conversion
        import sympy as sy
        consts = dict(hexbase=16, hexlen=256, bigbase=27)
        symbols = sy.symbols('hexbase, hexlen, bigbase, newlen')
        haexbase, hexlen, bigbase, newlen = symbols
        eqn = sy.Eq(16 ** hexlen,  bigbase ** newlen)
        newlen_ans = sy.solve(eqn, newlen)[0].subs(consts).evalf()
        print('newlen_ans = %r' % (newlen_ans,))

        # for a 27 char alphabet we can get 216
        print('Required length for lossless conversion len2 = %r' % (len2,))

        def info(base, len):
            bits = base ** len
            print('base = %r' % (base,))
            print('len = %r' % (len,))
            print('bits = %r' % (bits,))
        info(16, 256)
        info(27, 16)
        info(27, 64)
        info(27, 216)