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aica_xm: document constants

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This commit is contained in:
Zack Buhman 2025-06-23 09:48:35 -05:00
parent ff3f8f0837
commit ef29e0ac25
1 changed files with 6 additions and 1 deletions
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7
example/aica/aica_xm.cpp
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@ -376,6 +376,10 @@ void writeback(void const * const buf, uint32_t size)
}
// quater-semitones
//
// for i in range(48):
// round(1024 * (2 ** (i / 48) - 1))
//
const static int cent_to_fns[] = {
0, 15, 30, 45, 61, 77, 93, 109, 125, 142, 159, 176,
194, 211, 229, 248, 266, 285, 304, 323, 343, 363, 383, 403,
@ -387,6 +391,7 @@ const int cent_to_fns_length = (sizeof (cent_to_fns)) / (sizeof (cent_to_fns[0])
uint16_t
note_to_oct_fns(const int8_t note)
{
// log(8363 / 44100) / log(2)
const float base_ratio = -2.3986861877015477;
float c4_note = (float)note - 49.0;
@ -403,7 +408,7 @@ note_to_oct_fns(const int8_t note)
}
assert(fraction >= 0.0);
assert(fraction <= 1.0);
assert(fraction < 1.0);
int fns = cent_to_fns[(int)(fraction * cent_to_fns_length)];