def log_int_fixed(n, prec, ln2=None):
    """
    Fast computation of log(n), caching the value for small n,
    intended for zeta sums.
    """
    if n in log_int_cache:
        value, vprec = log_int_cache[n]
        if vprec >= prec:
            return value >> (vprec - prec)
    wp = prec + 10
    if wp <= LOG_TAYLOR_SHIFT:
        if ln2 is None:
            ln2 = ln2_fixed(wp)
        r = bitcount(n)
        x = n << (wp-r)
        v = log_taylor_cached(x, wp) + r*ln2
    else:
        v = to_fixed(mpf_log(from_int(n), wp+5), wp)
    if n < MAX_LOG_INT_CACHE:
        log_int_cache[n] = (v, wp)
    return v >> (wp-prec)
dataset/ETHPy150Open fredrik-johansson/mpmath/mpmath/libmp/libelefun.py/log_int_fixed/original