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Merge pull request #47 from jpcima/fast-pan

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Fast pan with lookup table
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JP Cimalando 2020-02-09 22:48:56 +01:00 • committed by GitHub
commit f0c4e77afd
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1 changed files with 31 additions and 3 deletions
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34
src/sfizz/SIMDHelpers.h
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@ -43,6 +43,7 @@
#include "MathHelpers.h"
#include <absl/algorithm/container.h>
#include <absl/types/span.h>
#include <array>
#include <cmath>
namespace sfz {
@ -723,12 +724,39 @@ template <>
void copy<float, true>(absl::Span<const float> input, absl::Span<float> output) noexcept;
namespace _internals {
// Number of elements in the table, odd for equal volume at center
constexpr int panSize = 4095;
// Table of pan values for the left channel, extra element for safety
const auto panData = []()
{
std::array<float, panSize + 1> pan;
int i = 0;
for (; i < panSize; ++i)
pan[i] = std::cos(i * (piTwo<double> / (panSize - 1)));
for (; i < static_cast<int>(pan.size()); ++i)
pan[i] = pan[panSize - 1];
return pan;
}();
template <class T>
inline void snippetPan(const T*& pan, T*& left, T*& right)
{
const auto circlePan = piFour<float> * (static_cast<T>(1.0) + *pan++);
*left++ *= std::cos(circlePan);
*right++ *= std::sin(circlePan);
T p = ((*pan++) + T{1.0}) * T{0.5};
p = clamp<T>(p, 0, 1);
auto lookUp = [](T pan) -> T
{
// reduce range, round to nearest
int index = static_cast<int>(T{0.5} + pan * (panSize - 1));
return panData[index];
};
*left++ = lookUp(p);
*right++ = lookUp(1 - p);
}
}