1 | * ------------------------------------------------------------------------------
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2 | * tofpu.s -- convert between millisecond time interval and FPU increment formats
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3 | * Version 9 -- 1987-12-21 -- D.N. Lynx Crowe
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4 | *
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5 | * unsigned short
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6 | * tofpu(time)
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7 | * unsigned short time;
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8 | *
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9 | * Converts 'time' in milliseconds to FPU format.
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10 | *
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11 | * unsigned short
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12 | * fromfpu(fputime)
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13 | * unsigned short fputime;
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14 | *
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15 | * Converts 'fputime' from FPU format to milliseconds.
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16 | * ------------------------------------------------------------------------------
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17 | .text
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18 | *
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19 | .xdef _tofpu
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20 | .xdef _fromfpu
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21 | *
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22 | TIME .equ 8 * WORD - time argument (either format)
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23 | *
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24 | TCYCL .equ $3B000000 * LONG - scaled FPU cycle time (.4608)
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25 | *
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26 | .page
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27 | _tofpu: link a6,#0 * link stack frames
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28 | move.w TIME(a6),d1 * get time interval
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29 | beq notime * jump if zero time
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30 | *
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31 | clr.w d2 * clear shift count
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32 | *
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33 | sloop: btst #15,d1 * see if MSB is set yet
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34 | bne gotexp * jump if so
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35 | *
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36 | lsl.w d1 * shift time left a bit
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37 | addq.w #1,d2 * increment the shift count
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38 | cmpi.w #15,d2 * see if we've hit the maximum
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39 | bne sloop * try again if not
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40 | *
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41 | gotexp: move.l #TCYCL,d0 * divide FPU cycle time by shifted value
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42 | divu d1,d0 * ...
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43 | andi.w #$FFF0,d0 * mask result
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44 | or.w d2,d0 * set the exponent
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45 | *
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46 | finis: unlk a6 * unlink stack frames
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47 | rts * return to caller
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48 | *
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49 | notime: clr.w d0 * zero time is zero ...
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50 | bra finis * return value for zero time
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51 | *
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52 | .page
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53 | _fromfpu: link a6,#0 * link stack frames
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54 | move.w TIME(a6),d1 * get FPU formatted time
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55 | beq zerotime * done if it's zero
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56 | *
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57 | move.w d1,d2 * extract shift count
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58 | andi.w #$000F,d2 * ...
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59 | andi.w #$FFF0,d1 * extract mantissa
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60 | beq zerotime * ... just in case it's zero (an error)
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61 | *
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62 | move.l #TCYCL,d0 * get FPU cycle time
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63 | divu d1,d0 * divide by mantissa
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64 | bvc divok * jump if divide ok
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65 | *
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66 | move.w #$FFFF,d0 * jam maximum value for overflow
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67 | *
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68 | divok: lsr.w d2,d0 * shift result into position
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69 | *
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70 | byebye: unlk a6 * unlink stack frames
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71 | rts * return to caller
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72 | *
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73 | zerotime: clr.l d0 * return a zero result
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74 | bra byebye * ...
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75 | *
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76 | .end
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