From: John Payson via Scott Dattalo
see
http://www.dattalo.com/technical/software/pic/bcd.txt
for notes on how this works. Plan on a headache. <GRIN>
[ed: quick guess at speed is that about 200 instructions will be executed
and 50 bytes + 7 registers used]
;Takes hex number in NumH:NumL Returns decimal in ;TenK:Thou:Hund:Tens:Ones ;written by John Payson ;input ;=A3*163 + A2*162 + A1*161 + A0*160 ;=A3*4096 + A2*256 + A1*16 + A0 NumH equ AD3M ;A3*16+A2 NumL equ AD3L ;A1*16+A0 ;share variables ;=B4*104 + B3*103 + B2*102 + B1*101 + B0*100 ;=B4*10000 + B3*1000 + B2*100 + B1*10 + B0 TenK equ LOOPER ;B4 Thou equ D2 ;B3 Hund equ D1 ;B2 Tens equ R2 ;B1 Ones equ R1 ;B0 mov W, <>NumH ;w = A2*16+A3 and W, #$0F ;w = A3 *** PERSONALLY, I'D REPLACE THESE 2 ;*** WARNING: ADDLW was expanded in three instructions! Check if previous instruction is a skip instruction. ; addlw $F0 ;w = A3-16 *** LINES WITH "IORLW 11110000B" -AW mov Hack, W mov W, #$F0 ;w = A3-16 *** LINES WITH "IORLW 11110000B" -AW add W, Hack mov Thou, W ;B3 = A3-16 add Thou, W ;B3 = 2*(A3-16) = 2A3 - 32 ;*** WARNING: ADDLW was expanded in three instructions! Check if previous instruction is a skip instruction. ; addlw $E2 ;w = A3-16 - 30 = A3-46 mov Hack, W mov W, #$E2 ;w = A3-16 - 30 = A3-46 add W, Hack mov Hund, W ;B2 = A3-46 ;*** WARNING: ADDLW was expanded in three instructions! Check if previous instruction is a skip instruction. ; addlw $32 ;w = A3-46 + 50 = A3+4 mov Hack, W mov W, #$32 ;w = A3-46 + 50 = A3+4 add W, Hack mov Ones, W ;B0 = A3+4 mov W, NumH ;w = A3*16+A2 and W, #$0F ;w = A2 add Hund, W ;B2 = A3-46 + A2 = A3+A2-46 add Hund, W ;B2 = A3+A2-46 + A2 = A3+2A2-46 add Ones, W ;B0 = A3+4 + A2 = A3+A2+4 ;*** WARNING: ADDLW was expanded in three instructions! Check if previous instruction is a skip instruction. ; addlw $E9 ;w = A2 - 23 mov Hack, W mov W, #$E9 ;w = A2 - 23 add W, Hack mov Tens, W ;B1 = A2-23 add Tens, W ;B1 = 2*(A2-23) add Tens, W ;B1 = 3*(A2-23) = 3A2-69 (Doh! thanks NG) mov W, <>NumL ;w = A0*16+A1 and W, #$0F ;w = A1 add Tens, W ;B1 = 3A2-69 + A1 = 3A2+A1-69 range -69...-9 add Ones, W ;B0 = A3+A2+4 + A1 = A3+A2+A1+4 and Carry = 0 (thanks NG) rl Tens ;B1 = 2*(3A2+A1-69) + C = 6A2+2A1-138 and Carry is now 1 as tens register had to be negitive rl Ones ;B0 = 2*(A3+A2+A1+4) + C = 2A3+2A2+2A1+9 (+9 not +8 due to the carry from prev line, Thanks NG) not Ones ;B0 = ~(2A3+2A2+2A1+9) = -2A3-2A2-2A1-10 (ones complement plus 1 is twos complement. Thanks SD) ;;Nikolai Golovchenko [golovchenko at MAIL.RU] says: comf can be regarded like: ;; not Ones ;; inc Ones ;; dec Ones ;;First two instructions make up negation. So, ;;Ones = -1 * Ones - 1 ;; = - 2 * (A3 + A2 + A1) - 9 - 1 ;; = - 2 * (A3 + A2 + A1) - 10 rl Ones ;B0 = 2*(-2A3-2A2-2A1-10) = -4A3-4A2-4A1-20 mov W, NumL ;w = A1*16+A0 and W, #$0F ;w = A0 add Ones, W ;B0 = -4A3-4A2-4A1-20 + A0 = A0-4(A3+A2+A1)-20 range -215...-5 Carry=0 rl Thou ;B3 = 2*(2A3 - 32) = 4A3 - 64 mov W, #$07 ;w = 7 mov TenK, W ;B4 = 7 ;B0 = A0-4(A3+A2+A1)-20 ;-5...-200 ;B1 = 6A2+2A1-138 ;-18...-138 ;B2 = A3+2A2-46 ;-1...-46 ;B3 = 4A3-64 ;-4...-64 ;B4 = 7 ;7 ; At this point, the original number is ; equal to TenK*10000+Thou*1000+Hund*100+Tens*10+Ones ; if those entities are regarded as two's compliment ; binary. To be precise, all of them are negative ; except TenK. Now the number needs to be normal- ; ized, but this can all be done with simple byte ; arithmetic. mov W, #$0A ;w = 10 Lb1: ;do add Ones, W ; B0 += 10 dec Tens ; B1 -= 1 sb 3.0 ;skip no carry jmp Lb1 ; while B0 < 0 ;jmp carry Lb2: ;do add Tens, W ; B1 += 10 dec Hund ; B2 -= 1 sb 3.0 jmp Lb2 ; while B1 < 0 Lb3: ;do add Hund, W ; B2 += 10 dec Thou ; B3 -= 1 sb 3.0 jmp Lb3 ; while B2 < 0 Lb4: ;do add Thou, W ; B3 += 10 dec TenK ; B4 -= 1 sb 3.0 jmp Lb4 ; while B3 < 0 retw #0