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1706
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1 *
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2 * Arithmetic routines for VIEW
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3 *
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4 *
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5 ifp1
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1912
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6 use os9defs.d
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1706
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7 endc
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8
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9 psect view_arith_a,0,0,0,0,0
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10 *
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11 * Divide A by B, return fixed-point result in A.B, rounded.
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12 *
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13 divAB:
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14 pshs b Put divisor on stack
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15 ldb #17 17-bit result, with last bit in C.
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16 pshs b
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17 clrb
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18 pshs b
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19 divABloop
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20 rol ,s
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21 rola
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22 rolb Shift into B.
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23 cmpb 2,s
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24 blo divAB1
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25 subb 2,s
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26 orcc #Carry
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27 bra divAB2
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28 divAB1
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29 andcc #^Carry
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30 divAB2
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31 dec 1,s
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32 bne divABloop
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33 puls b Get fraction part into B
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34 adcb #0 Round by adding in extra decimal place.
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35 adca #0
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36 leas 2,s Clear up stack.
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37 rts
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38
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39 * Divide 16-bit value in X by 8-bit value in A, return 16-bit result in D.
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40 *
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41 div168:
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42 pshs x The division we want is (XH * 256 + XL) / A
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43 pshs d
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44 lda 3,s First, calculate XL / A
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45 ldb ,s
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46 bsr divAB
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47 sta 1,s Save it.
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48 lda 2,s Now do (XH/A) *256
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49 ldb ,s
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50 clr ,s
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51 bsr divAB
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52 addd ,s Add them to get answer.
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53 std ,s
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54 puls d
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55 puls x,pc
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56
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57 endsect
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