I found a way to reduce the control to only 3 wires. It is an extension to the method described in the previous log. The NOT A function was dropped, this can also be done with XOR FF or XNOR 0.

Only four gates are needed. It is based on the observation that the combination M1 = 0 and M3 = 0 was not used. This combination is now detected by the leftmost NOR gate, and this sets the F0 control wire HIGH, and sets the F1 signal HIGH to create the SUB (B-A) and XNOR function.

The XNOR function can be used to check if two values are equal. The XNOR will result in a FF value in this case, and that can be detected by using a 74HC30 (8-input NAND gate, 14 pins). If XOR was used for compare, equality would result in a zero value, and to detect that we would need an 8-input OR gate, that does not exist in a single package (unless the big 74HC688 is used, 20 pins).

Here is the new function table, sorted according to the 3-bit control value.

The PCB's were ordered today, I hope to have them within 10 days.