Comment by lifthrasiir

You can also premultiply w with a, as every occurrence of `w` looks like `w*a`. This should shave three more bytes:

  w=g-g*exp(...),g-=w*a,c+=w*a*d*9.+...,c.r+=w*a*a*2,...
  w=g-g*exp(...),g-=w*=a,c+=w*d*9.+...,c.r+=w*a*2,...

(I've tested this with the Shadertoy version. YMMV.)