typedef enum : int {
    None  = 0,
    ReLU  = 1,
    ReLU6 = 2,
} conv_activation_type;

inline ftype4 activate(ftype4 value, conv_activation_type type) {
    switch (type) {
        case ReLU:
            return max(value, (ftype4)0);
        case ReLU6:
            return clamp(value, (ftype4)0, (ftype4)6);
        default: // None
            return value;
    }
}