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added quick and dirty decibel approximation

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This commit is contained in:
Ahmet Inan 2019-01-21 11:36:50 +01:00
commit 97d5b68045
1 changed files with 20 additions and 0 deletions
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20
utils.hh
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@ -43,7 +43,27 @@ TYPE delta(TYPE x)
template <typename TYPE>
TYPE decibel(TYPE v)
{
#if 0
return TYPE(10) * log10(v);
#else
static constexpr TYPE
// 2*1024*10/l(10)
scale = 8894.350989378597430295120259412072085389250678859091274024013479236L,
inv1 = TYPE(1) / TYPE(1),
inv3 = TYPE(1) / TYPE(3),
inv5 = TYPE(1) / TYPE(5),
inv7 = TYPE(1) / TYPE(7),
inv9 = TYPE(1) / TYPE(9),
inv11 = TYPE(1) / TYPE(11),
inv13 = TYPE(1) / TYPE(13);
TYPE x = v;
for (int i = 0; i < 10; ++i)
x = sqrt(x);
x = (x - TYPE(1)) / (x + TYPE(1));
TYPE xx = x * x;
return scale * x * (xx * (xx * (xx * (xx * (xx * (xx *
inv13 + inv11) + inv9) + inv7) + inv5) + inv3) + inv1);
#endif
}
}