|| beta definitions
.include beta

.macro MyMUL(ra, rb, rc) betaop(0x07, ra, rb, rc)
.macro MyMULC(ra, c, rc) betaopc(0x0F, ra, c, rc)

|| start:
BR(main) 
|| illegal op:
BR(IllegalOp)

SavedRegs:
        .= .+32

.macro SAVE(Rn)  ST(Rn, SavedRegs+Rn, r31)
.macro RSTR(Rn)  LD(r31, SavedRegs+Rn, Rn)

IllegalOp:
        | save state
        SAVE(r0)  SAVE(r1)  SAVE(r2)   SAVE(r3)
        SAVE(r4)  SAVE(r5)  SAVE(r6)   SAVE(r7)
        SAVE(r8)  SAVE(r9)  SAVE(r10)  SAVE(r11)
        SAVE(r12) SAVE(r13) SAVE(r14)  SAVE(r15)
        SAVE(r16) SAVE(r17) SAVE(r18)  SAVE(r19)
        SAVE(r20) SAVE(r21) SAVE(r22)  SAVE(r23)
        SAVE(r24) SAVE(r25) SAVE(r26)  SAVE(r27)
        SAVE(r28) SAVE(r29) SAVE(r30)  SAVE(r31)

        LD(xp, -1, r0)          | load [xp-1] (illegal instruction) into r0
        SHRC(r0, 26, r0)        | shift right to get the actual opcode
        LD(r0, optable, r0)     | load trap address from table into r0
        JMP(r0)

UNK = UnknownOp

optable:
        UNK UNK UNK UNK UNK UNK UNK Mult
        UNK UNK UNK UNK UNK UNK UNK MultC
        UNK UNK UNK UNK UNK UNK UNK UNK
        UNK UNK UNK UNK UNK UNK UNK UNK
        UNK UNK UNK UNK UNK UNK UNK UNK
        UNK UNK UNK UNK UNK UNK UNK UNK
        UNK UNK UNK UNK UNK UNK UNK UNK
        UNK UNK UNK UNK UNK UNK UNK UNK

UnknownOp:
        HALT()

Mult:
        || get Rb into r2
        LD(xp, -1, r0)          | load illegal instruction into r0
        SHRC(r0, 5, r2)         |
        ANDC(r2, 31, r2)        | r2 now holds Rb
        LD(r2, SavedRegs, r2)   | r2 now holds <Rb>
        BR(GetRa)

MultC:
        || fetch constant into r2
        LD(xp, -1, r0)          | load illegal instruction into r0
        SHLC(r0, 32-16-5, r2)   | shove constant up to high end
        SRAC(r2, 16, r2)        | bring constant back arithmetically

GetRa:
        | get Ra into r1
        LD(xp, -1, r0)          | load illegal instruction into r0
        SHRC(r0, 21, r1)        |        
        ANDC(r1, 31, r1)        | r1 now holds Ra
        LD(r1, SavedRegs, r1)   | r1 now holds <Ra>


DoMult:                 || r0 will be product
                        || r1 will be multiplier
                        || r2 will be multiplicand
                        || r3 will be testing value
        CMPLTC(r1, 0, r3)
        BF(r3, propersign)
        SUB(r31, r1, r1)
        SUB(r31, r2, r2)
propersign:
        MOVC(0, r0)     || initialize product
loop:   
        ANDC(r1, 1, r3)
        BZ(r3, shift)
        ADD(r2, r0, r0)
shift:  SHRC(r1, 1, r1)
        SHLC(r2, 1, r2)
        BNZ(r1, loop)

|| answer is now in r0

        LD(xp, -1, r1)          | load illegal instruction into r0
        ANDC(r1, 31, r1)        | r1 now holds Rc
        ST(r0, SavedRegs, r1)   | save value into saved regs

RestoreState:
        RSTR(r0)  RSTR(r1)  RSTR(r2)   RSTR(r3)
        RSTR(r4)  RSTR(r5)  RSTR(r6)   RSTR(r7)
        RSTR(r8)  RSTR(r9)  RSTR(r10)  RSTR(r11)
        RSTR(r12) RSTR(r13) RSTR(r14)  RSTR(r15)
        RSTR(r16) RSTR(r17) RSTR(r18)  RSTR(r19)
        RSTR(r20) RSTR(r21) RSTR(r22)  RSTR(r23)
        RSTR(r24) RSTR(r25) RSTR(r26)  RSTR(r27)
        RSTR(r28) RSTR(r29) RSTR(r30)  RSTR(r31)
        JMP(xp)

main:
        MOVC(stack, sp)
        MOVC(10, r0)
        MOVC(-5, r5)
        MyMUL(r0, r5, r7)
        MyMULC(r0, -5, r8)
        HALT()

stack: