Here is an alternative that MIGHT be acceptable.
in combiner 0 alpha, calculate tex0 + (1-tex1). Since tex0 & tex1 are in the 0 to 1 range, output is in the 0 to 2 range. Scale output by 1/2, and we now have it back into the 0 to 1 range. Store this in spare 0 alpha.
in combiner 1 alpha:
A = 1
B = spare 0 alpha - 0.5
C = -1
D = spare 0 alpha - 0.5
use the mux function and scale the output by 2. Store the result in spare 0 alpha
in the final combiner, select spare 0 alpha into G
If I figured everything correctly, this should get you the absolute value of tex0-tex1. The one thing to note here is that since we scale by 1/2 before storing to spare 0, you will lose some precision in the calculation (unless the register combiners’ registers have at least 9 bits of preceission, and I cant remember if they do or not).