keras/src/activations/activations.py/hard_sigmoid
def hard_sigmoid(x):
    """Hard sigmoid activation function.

    The hard sigmoid activation is defined as:

    - `0` if `if x <= -3`
    - `1` if `x >= 3`
    - `(x/6) + 0.5` if `-3 < x < 3`

    It's a faster, piecewise linear approximation
    of the sigmoid activation.

    Args:
        x: Input tensor.

    Reference:

    - [Wikipedia "Hard sigmoid"](https://en.wikipedia.org/wiki/Hard_sigmoid)
    """
    return ops.hard_sigmoid(x)