For the contest...

Okay, I have been able to test the routine, and in fact it did work first time it executed... It didn't assemble first time because I had left out a local symbol, but with that corrected it built on the second try. In designing the algorithm I used, I noted that converting to Roman is the same as converting a binary value to decimal (finding the digit 0-9 for a given power-of-ten) but with the added step of converting that digit to the appropriate characters for the given power-of-ten. The routine has a table of values which are used for successively subtracting a power of ten from the value until it has a digit 0-9 and a remainder (which is handled by decreasing powers of ten on successive passes through the loop). It also maintains a pointer to the current roman numeral corresponding with the current power-of-ten. The conversion for 0-3 is easy, it simply outputs the requisite number of the current roman numeral. For 4, it outputs the current numeral followed by the numeral one higher. For 5-8, it starts by printing the numeral one higher followed by 0-3 of the current numeral. For 9, it outputs the current numeral followed by the numeral two higher. At the end of each loop, the power-of-ten pointer is incremented to the next entry, but the pointer to the roman numeral is also incremented by two. This way, the 'current numeral' pointer is always pointing to 'M', 'C', 'X', or 'I'. Since no number in the range which can be converted required numerals above 'M', I only have to worry about C, X and I. The numeral one higher than each is, respectively, D, L and V. The numeral two higher than each is, respectively, M, C and X. That's it... I didn't get info on cycles, but I did for number of instructions, which I included in the comments for the routine. One last thing - since there are quite a few members in the family of pdp-11 CPUs, the code is written to run correctly on any one of them. There are no restrictions, so using the T-11 (as I think Allison mentioned) would be possible. Megan Gentry Former RT-11 Developer +--------------------------------+-------------------------------------+ | Megan Gentry, EMT/B, PP-ASEL | Internet (work): gentry(a)zk3.dec.com | | Unix Support Engineering Group | (home): mbg(a)world.std.com | | Compaq Computer Corporation | | | 110 Spitbrook Rd. ZK03-2/T43 | URL: http://world.std.com/~mbg/ | | Nashua, NH 03062 | "pdp-11 programmer - some assembler | | (603) 884 1055 | required." - mbg | +--------------------------------+-------------------------------------+ - - - - - .SBTTL CVBTAR - Convert Binary to Ascii Roman Numerals ;+ ; ; Copyright (c) 1999 by Megan Gentry ; ; CVBTAR ; Converts a binary value to string of ascii characters which ; represent the value in Roman Numerals. ; ; Call: ; R0 = Binary value to convert ; R1 -> Storage space for resulting string (nul-terminated) ; ; Returns: ; R0 = zero ; R1 -> Byte beyond end of nul-terminated string ; other registers are unaffected as they are saved and restored ; ; Notes: ; o Valid range for input is 1 to 3999. ; o Roman numerals are: ; M 1000 ; D 500 ; C 100 ; L 50 ; X 10 ; V 5 ; I 1 ; ; 60 words (120 bytes) of code ; 5 words (10 bytes) of data ; 7 bytes of text ; 3 words (6 bytes) of stack used ; ; Code ROMable: yes ; Data ROMable: yes ; Code Reentrant: yes ; Data Reentrant: yes ; Undefined opcodes: no ; Undefined behaviour: no ; ; Value Instructions executed ; 0 5 ; 4000 7 ; 1 78 ; 3999 185 ; 3888 220 ; ;- .PSECT .CODE. .ENABL LSB CVBTAR: ; Range check the input TST R0 ;Is it valid? BLE 100$ ;Nope... CMP R0,#3999. ;Maybe, check upper limit... BGT 100$ ;Nope... ; Save registers and do some setup MOV R2,-(SP) ;Save R2 MOV R3,-(SP) ; and R3 while they are used MOV #BTDTAB,R2 ;R2 -> Decimal conversion table MOV #ROMCHR,R3 ;R3 -> Roman numeral character list BR 20$ ;Just starting conversion... ; Head of the loop 10$: TST @R2 ;End of the conversion table? BEQ 90$ ;Yep, conversion should be complete 20$: MOV R0,-(SP) ;Save current binary on stack CLR R0 ;Reset R0 for conversion 30$: INC R0 ;Bump count for this digit SUB @R2,@SP ;Reduce by current factor of 10 BHIS 30$ ;Continue if still positive... ADD (R2)+,@SP ;We went too far, add it back ; (and bump conversion table pointer) ; remainder is still on stack DEC R0 ;Reduce the count BEQ 80$ ;If zero, no characters to output ; Here we convert the decimal digit to Roman Numerals CMP R0,#9. ;Is it a nine? BNE 40$ ;Nope... MOVB @R3,(R1)+ ;Yes, it converts to current numeral MOVB -2(R3),(R1)+ ; followed by the numeral two higher BR 80$ 40$: CMP R0,#4. ;Is it a four? BNE 50$ ;Nope... MOVB @R3,(R1)+ ;Yes, it converts to current numeral MOVB -1(R3),(R1)+ ; followed by the numeral one higher BR 80$ 50$: SUB #5.,R0 ;Is value five or greater? BLT 60$ ;Nope, in range zero to three MOVB -1(R3),(R1)+ ;Yes, prefix with one higher numeral SUB #5.,R0 ; followed by one to three current 60$: ADD #5.,R0 ;Return value to range zero to three BEQ 80$ ;It was zero, nothing to do... 70$: MOVB @R3,(R1)+ ;Store a numeral DEC R0 ;More to do? BGT 70$ ;Yep... ; Tail of the loop 80$: ADD #2,R3 ;Bump the numeral pointer by *2* MOV (SP)+,R0 ;Pop the remainder (already popped ; the power of ten pointer) BNE 10$ ;More conversion to do if non-zero ; Clean-up 90$: MOV (SP)+,R3 ;Restore previously saved R3 MOV (SP)+,R2 ; and R2 BR 110$ ; Out-of-range string 100$: MOVB #'*,(R1)+ ;Out-of-range conversion string ; String termination and return 110$: CLRB (R1)+ ;String is to be nul-terminated RETURN .DSABL LSB ; Conversion data .PSECT .DATA. ; Binary to decimal conversion table BTDTAB: .WORD 1000. .WORD 100. .WORD 10. .WORD 1. .WORD 0 ; ** Table Fence ** .PSECT .TEXT. ; Roman Numerals (1st, 3rd... entries match entries in BTDTAB) ROMCHR: .ASCII /MDCLXVI/ .EVEN .END