diff options
Diffstat (limited to 'common/sinetables.cpp')
| -rw-r--r-- | common/sinetables.cpp | 40 |
1 files changed, 31 insertions, 9 deletions
diff --git a/common/sinetables.cpp b/common/sinetables.cpp index c01705e3dc..c85a7bf7cf 100644 --- a/common/sinetables.cpp +++ b/common/sinetables.cpp @@ -32,17 +32,39 @@ SineTable::SineTable(int bitPrecision) { _bitPrecision = bitPrecision; - int m = 1 << _bitPrecision; - double freq = 2 * M_PI / m; - _table = new float[m / 2]; + _nPoints = 1 << _bitPrecision; + _radResolution = 2.0 * M_PI / _nPoints; + _refSize = _nPoints / 4; + _table = new float[_nPoints / 2]; - // Table contains sin(2*pi*i/m) for 0<=i<m/4, - // followed by m/2<=i<3m/4 - for (int i = 0; i < m / 4; i++) - _table[i] = sin(i * freq); + // Table contains sin(2*pi*i/_nPoints) for 0<=i<_nPoints/4, + // followed by _nPoints/2<=i<3_nPoints/4 + for (int i = 0; i < _nPoints / 4; i++) + _table[i] = sin(i * _radResolution); - for (int i = 0; i < m / 4; i++) - _table[m / 4 + i] = -_table[i]; + for (int i = 0; i < _nPoints / 4; i++) + _table[_nPoints / 4 + i] = -_table[i]; + +} + +float SineTable::at(int index) const { + assert((index >= 0) && (index < _nPoints)); + if (index < _refSize) + // [0,pi/2) + return _table[index]; + if (index == _refSize) + // pi/2 + return 1.0f; // sin(pi/2) = 1.0 + if ((index > _refSize) && (index < 2 * _refSize)) + // (pi/2,pi) + return _table[2 * _refSize - index]; + if ((index >= 2 * _refSize) && (index < 3 * _refSize)) + // [pi,3/2pi) + return -_table[index - 2 * _refSize]; + if ((index > 3 * _refSize) && (index < _nPoints)) + // (3/2pi,2pi) + return -_table[_nPoints - index]; + return -1.0f; // sin(3pi/2) = -1.0 } SineTable::~SineTable() { |