Some from the 1960s. Quoting numpy/lib/function_base.py:

    We use the algorithm published by Clenshaw [1]_ and referenced by
    Abramowitz and Stegun [2]_, for which the function domain is ...
    .. [1] C. W. Clenshaw, "Chebyshev series for mathematical functions", in
           *National Physical Laboratory Mathematical Tables*, vol. 5, London:
           Her Majesty's Stationery Office, 1962.
    .. [2] M. Abramowitz and I. A. Stegun, *Handbook of Mathematical
           Functions*, 10th printing, New York: Dover, 1964, pp. 379.
           http://www.math.sfu.ca/~cbm/aands/page_379.htm

Quoting numpy/core/src/npymath/npy_math_complex.c.src:

    /* Algorithm 312, CACM vol 10, Oct 1967. */
    if (a >= 0) {
        t = npy_sqrt@c@((a + npy_hypot@c@(a, b)) * 0.5@c@);
        result = npy_cpack@c@(t, b / (2 * t));
    }