Interpolation

var e = se.m_fRecencyValue * (O.NUM_RECENCY_STEPS - 1 - .001),
    t = Math.floor(e),
    a = t + 1,
    r = 1 - (e - t),
    n = 1 - r,
    o = se.m_fPopularityValue * (O.NUM_POPULARITY_STEPS - 1 - .001),
    i = Math.floor(o),
    c = i + 1,
    l = 1 - (o - i),
    s = 1 - l,

u = [];
u.push({ index: i * O.NUM_RECENCY_STEPS + t, weight: l * r }),
u.push({ index: c * O.NUM_RECENCY_STEPS + t, weight: s * r }),
u.push({ index: i * O.NUM_RECENCY_STEPS + a, weight: l * n }),
u.push({ index: c * O.NUM_RECENCY_STEPS + a, weight: s * n });

for (var _ = new Map, p = 0, d = 0, h = u; d < h.length; d++) {
    var m = h[d],
    E = N[m.index]; if (p = Math.max(p, E.score_scale), E)
    for (var v = 0; v < E.app_ids.length; v++) {
        var b = E.app_ids[v]; if (D[b] && !D[b].o && !D[b].i) {
            var g = (_.get(b) || 0) + E.scores[v] * m.weight * E.score_scale;
            _.set(b, g)
        }
    }
}
_.forEach(function(e, t) { return _.set(t, e / p) }); var f = [];

_.forEach(function(e, t) { return f.push({ appid: t, score: e }) }),

Reference: javascript code archived here.