def _rspiral(width, height):
        """Reversed spiral generator.

        Parameters
        ----------
        width : `int`
            Spiral width.
        height : `int`
            Spiral height.

        Returns
        -------
        `generator` of (`int`, `int`)
            Points.
        """

        x0 = 0
        y0 = 0
        x1 = width - 1
        y1 = height - 1

        while x0 < x1 and y0 < y1:
            for x in range(x0, x1):
                yield x, y0
            for y in range(y0, y1):
                yield x1, y
            for x in range(x1, x0, -1):
                yield x, y1
            for y in range(y1, y0, -1):
                yield x0, y

            x0 += 1
            y0 += 1
            x1 -= 1
            y1 -= 1

        if x0 == x1:
            for y in range(y0, y1 + 1):
                yield x0, y
        elif y0 == y1:
            for x in range(x0, x1 + 1):
                yield x, y0
Reversed spiral generator.

        Parameters
        ----------
        width : `int`
            Spiral width.
        height : `int`
            Spiral height.

        Returns
        -------
        `generator` of (`int`, `int`)
            Points.