nx_alu_select.nx

nx_alu_select.nx -- THE one ALU op-select builder, written against NxCellSink. Called with a MEM sink it fills an NxGsim the Verifier runs; called with a TEXT sink it emits the .nxgate the shipping synth ships. Same code -> the verifier proves exactly what the emitter ships (one source, two sinks). Topology (per op K in 1..N-1): CONST(K) opcode + subnet + EQ(op_in==K) match; then a cascade MUX(match_K, subnet_K, prev). use_divider=1 makes DIV/DIVU take the PROVEN restoring divider's quotient and REM/REMU its remainder (the first hardware invention, in the shipped ALU); use_divider=0 keeps the single-cell stub from the single-source op->kind map (the baseline that catches holes). na/nb/nop are pre-existing net ids for a / b / op_in in the sink's net space. Returns the cascade result net id (caller wires it to the result port / records it as the sim output).