creating orient and rotating points around vector

I think Toadstorm posted this somewhere on odforce... but it's a useful little vex snippet

 vector fwd = v@N;

vector up = {0,1,0};
// if you don't have a defined up vector but want to compute one the way houdini does it natively,
// compute the rotation that rotates +Z to N and apply this to +Y...
// matrix3 d = dihedral({0,0,1}, fwd);
// up = normalize(d * up);matrix3 m = maketransform(fwd, up);
// now you can rotate this around whatever axis you want.
vector axis = normalize(chv("axis")); // or use an existing vector attribute!
float angle = @noiseVal*radians(ch("angle")); // or use a random float attribute!
rotate(m, angle, axis);// now convert this rotated matrix to a quaternion and bind to p@orient. copy to points and/or DOPs will understand this.
@orient = quaternion(m);