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#755 fix, sin_f32 fails at 180

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#755 fix, sin_f32 returns incorrect result at 180 degrees, clean up
This commit is contained in:
rusty.labs 2022-12-28 01:13:42 -05:00
parent 25c267a3d9
commit e69c9bbc7b
1 changed files with 10 additions and 14 deletions
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24
firmware/common/sine_table.hpp
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@ -35,11 +35,9 @@ w = numpy.arange(length, dtype=numpy.float64) * (2 * numpy.pi / length)
v = numpy.sin(w) v = numpy.sin(w)
print(v) print(v)
*/ */
constexpr size_t sine_table_f32_period_log2 = 8; constexpr uint16_t sine_table_f32_period = 256;
constexpr size_t sine_table_f32_period = 1 << sine_table_f32_period_log2;
constexpr uint32_t sine_table_f32_index_mask = sine_table_f32_period - 1;
static constexpr std::array<float, sine_table_f32_period + 1> sine_table_f32 { { static constexpr std::array<float, sine_table_f32_period + 2> sine_table_f32{
0.00000000e+00, 2.45412285e-02, 4.90676743e-02, 0.00000000e+00, 2.45412285e-02, 4.90676743e-02,
7.35645636e-02, 9.80171403e-02, 1.22410675e-01, 7.35645636e-02, 9.80171403e-02, 1.22410675e-01,
1.46730474e-01, 1.70961889e-01, 1.95090322e-01, 1.46730474e-01, 1.70961889e-01, 1.95090322e-01,
@ -125,24 +123,22 @@ static constexpr std::array<float, sine_table_f32_period + 1> sine_table_f32 { {
-2.42980180e-01, -2.19101240e-01, -1.95090322e-01, -2.42980180e-01, -2.19101240e-01, -1.95090322e-01,
-1.70961889e-01, -1.46730474e-01, -1.22410675e-01, -1.70961889e-01, -1.46730474e-01, -1.22410675e-01,
-9.80171403e-02, -7.35645636e-02, -4.90676743e-02, -9.80171403e-02, -7.35645636e-02, -4.90676743e-02,
-2.45412285e-02, 0.00000000e+00, -2.45412285e-02, 0.00000000e+00, 0.00000000e+00
} }; };
inline float sin_f32(const float w) { inline float sin_f32(const float w) {
constexpr float normalize = 1.0 / (2 * pi); const float x = w / (2 * pi); // normalization
const float x_frac = x - std::floor(x); // [0, 1]
const float x = w * normalize;
const int32_t x_int = std::floor(x);
const float x_frac = x - x_int;
const float n = x_frac * sine_table_f32_period; const float n = x_frac * sine_table_f32_period;
const int32_t n_int = static_cast<uint32_t>(n) & sine_table_f32_index_mask; const uint16_t n_int = static_cast<uint16_t>(n);
const float n_frac = n - n_int; const float n_frac = n - n_int;
const float p0 = sine_table_f32[n_int + 0]; const float p0 = sine_table_f32[n_int];
const float p1 = sine_table_f32[n_int + 1]; const float p1 = sine_table_f32[n_int + 1];
const float diff = p1 - p0; const float diff = p1 - p0;
const float result = p0 + n_frac * diff; const float result = p0 + n_frac * diff; // linear interpolation
return result; return result;
} }