Photoshop-style Overlay blend mode

Most of the main blend modes that someone using Photoshop might be used to are accounted for in Shapes, but the 'Overlay' blend mode, which is like a hybrid of both Multiply and Screen, is not yet included.

As an example, here is an implementation that has worked for me in the past, though I make no claims to its correctness:

#define BLEND_OVERLAY(a, b) b <= 0.5 ? (2*b)*a : (1 - (1-2*(b-0.5)) * (1-a)) 
half3 overlayBlend(half3 back, half3 front)
{
    return
        half3(
            BLEND_OVERLAY(back.r, front.r),
            BLEND_OVERLAY(back.g, front.g),
            BLEND_OVERLAY(back.b, front.b)
        );
}

Referenced from here: http://www.deepskycolors.com/archive/2010/04/21/formulas-for-Photoshop-blending-modes.html