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annotate lib/alib/div16x8.a @ 2474:7d70b7e1cb21

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Moved net and alib files into here
author boisy
date Tue, 30 Mar 2010 02:44:42 +0000
parents
children aaba193af04f
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2474
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1 ****************************************
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2 * 16 x 8 bit integer divide
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3
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4 * Result must be an 8 bit value
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5
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6 * ENTRY: A = divisor
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7 * X = dividend
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8
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9 * EXIT: A = remainder
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10 * B = quotient
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11 * all other registers (except CC) preserved
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12
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13 nam 16x8 bit Divide
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14 ttl Assembler Library Module
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15
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16
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17 psect DIV168,0,0,0,0,0
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18
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19 vsect
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20 negcount rmb 1
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21 endsect
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22
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23 * Signed Divide
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24 SDIV168:
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25 clr negcount,u
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26 PSHS A,X
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27 tst ,s
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28 bpl testquo
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29 lda ,s
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30 coma
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31 inca
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32 sta ,s
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33 inc negcount,u
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34 testquo
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35 tst 1,s
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36 bpl ok
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37 ldd 1,s
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38 comb
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39 coma
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40 addd #$0001
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41 std 1,s
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42 inc negcount,u
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43 ok
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44 puls a,x
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45 bsr DIV168
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46 dec negcount,u
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47 bne goforit
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48 pshs a,x
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49 lda ,s
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50 coma
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51 inca
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52 sta ,s
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53 ldd 1,s
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54 coma
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55 comb
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56 addd #$0001
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57 std 1,s
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58 puls a,x
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59 goforit
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60 rts
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61
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62
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63 DIV168:
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64 LDB #8 bit counter
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65 PSHS A,B,X save count and divisor and value
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66 TFR X,D put dividend in D
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67
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68 div1
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69 ASLB shift dividend and quotient
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70 ROLA
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71 CMPA 0,S is trial subtraction successful?
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72 BCS div2
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73 SUBA 0,S yes, subtract and set bit
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74 INCB in quotient
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75
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76 div2
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77 DEC 1,S count down bits
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78 BNE div1 loop till done
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79 LEAS 2,S clean stack
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80 PULS X,PC return
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81
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82 endsect
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83