Rewrite Type 9/9a decode: five sub-encodings
Type 9a (register-file, unconditional):
- XREG=bits11-8 (4 bits), YREG=bits3-0 (4 bits), both reg0[]
- Discriminated by bits5-4 = 10
- Verified: ar=mx0 xor my0, mr=ax0*ay0(ss)
Type 9 standard (conditional):
- XOP=bits10-8, YOP=bits12-11, COND=bits3-0
- bits7-4 = 0000 required
- Verified: all ALU ops, conditional MAC
Type 9 YOP=0:
- bits12-11 = 11, bits7-4 = 0000
- Renders f(xop, 0)
Type 9 MAC squaring:
- bits12-11 = 00, bit4 = 1, bits7-5 = 000
- Renders f(xop^2)
Type 9 constant YOP:
- CC=bits7-6, BO=bits5-4
- Renders f(xop, const)
Tested with open21xx assembler output for 15 instructions.
Full regression: isa_test, fir, iir unchanged.
1c28f027b8