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Routines |
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The address of this routine is found in the table of addresses. It is called via the calculator literal +1F by the routines at DRAW, CD_PRMS1 and tan. It is also called indirectly via fp_calc_2.
This subroutine handles the function SIN X and is the third of the four routines that use the series generator to produce Chebyshev polynomials.
The approximation to SIN X is found as follows:
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sin | 37B5 | RST $28 | X | |||||
Perform step i.
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37B6 | DEFB $39 | get_argt: W | ||||||
Perform step ii. The subroutine from now on is common to both the SINE and COSINE functions.
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C_ENT | 37B7 | DEFB $31 | duplicate: W, W | |||||
37B8 | DEFB $31 | duplicate: W, W, W | ||||||
37B9 | DEFB $04 | multiply: W, W*W | ||||||
37BA | DEFB $31 | duplicate: W, W*W, W*W | ||||||
37BB | DEFB $0F | addition: W, 2*W*W | ||||||
37BC | DEFB $A1 | stk_one: W, 2*W*W, 1 | ||||||
37BD | DEFB $03 | subtract: W, 2*W*W-1=Z | ||||||
Perform step iii, passing to the series generator the parameter '6' and the six constants required.
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37BE | DEFB $86 | series_06: W, Z | ||||||
37BF | DEFB $14,$E6 | |||||||
37C1 | DEFB $5C,$1F,$0B | |||||||
37C4 | DEFB $A3,$8F,$38,$EE | |||||||
37C8 | DEFB $E9,$15,$63,$BB,$23 | |||||||
37CD | DEFB $EE,$92,$0D,$CD,$ED | |||||||
37D2 | DEFB $F1,$23,$5D,$1B,$EA | |||||||
At the end of the last loop the 'last value' is (SIN (π*W/2))/W.
Perform step iv.
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37D7 | DEFB $04 | multiply: SIN (π*W/2)=SIN X (or COS X) | ||||||
37D8 | DEFB $38 | end_calc | ||||||
37D9 | RET | Finished: 'last value'=SIN X (or COS X). |
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