Spectrum ROM | 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 | 14261 | RST 40 | X | ||||
Perform step i.
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14262 | DEFB 57 | 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 | 14263 | DEFB 49 | duplicate: W, W | ||||
14264 | DEFB 49 | duplicate: W, W, W | |||||
14265 | DEFB 4 | multiply: W, W*W | |||||
14266 | DEFB 49 | duplicate: W, W*W, W*W | |||||
14267 | DEFB 15 | addition: W, 2*W*W | |||||
14268 | DEFB 161 | stk_one: W, 2*W*W, 1 | |||||
14269 | DEFB 3 | 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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14270 | DEFB 134 | series_06: W, Z | |||||
14271 | DEFB 20,230 | ||||||
14273 | DEFB 92,31,11 | ||||||
14276 | DEFB 163,143,56,238 | ||||||
14280 | DEFB 233,21,99,187,35 | ||||||
14285 | DEFB 238,146,13,205,237 | ||||||
14290 | DEFB 241,35,93,27,234 | ||||||
At the end of the last loop the 'last value' is (SIN (π*W/2))/W.
Perform step iv.
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14295 | DEFB 4 | multiply: SIN (π*W/2)=SIN X (or COS X) | |||||
14296 | DEFB 56 | end_calc | |||||
14297 | RET | Finished: 'last value'=SIN X (or COS X). |
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