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Merge 07aa5c13b5 into febd4caeed

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Charles Karney 2025-02-20 17:26:51 +02:00 committed by GitHub
commit f1a6602804
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1 changed files with 26 additions and 6 deletions
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kissfft.hh
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@ -25,12 +25,31 @@ class kissfft
:_nfft(nfft)
,_inverse(inverse)
{
using std::acos; using std::cos; using std::sin;
// fill twiddle factors
_twiddles.resize(_nfft);
const scalar_t phinc = (_inverse?2:-2)* std::acos( (scalar_t) -1) / _nfft;
for (std::size_t i=0;i<_nfft;++i)
_twiddles[i] = std::exp( cpx_t(0,i*phinc) );
{
const scalar_t s = _inverse ? 1 : -1;
const scalar_t d = acos( (scalar_t) -1) / (2 * _nfft);
int i = 0, N = _nfft; // signed ints needed for subtractions
// enforce trigonometric symmetries by evaluating sin and cos
// with arguments in the range [-pi/4, pi/4]
for (; 8*i < N; ++i)
_twiddles[i] = cpx_t(+ cos((4*i )*d),
+s*sin((4*i )*d)); // pi/4*[0, 1)
for (; 8*i < 3*N; ++i)
_twiddles[i] = cpx_t(- sin((4*i- N)*d),
+s*cos((4*i- N)*d)); // pi/4*[1, 3)
for (; 8*i < 5*N; ++i)
_twiddles[i] = cpx_t(- cos((4*i-2*N)*d),
-s*sin((4*i-2*N)*d)); // pi/4*[3, 5)
for (; 8*i < 7*N; ++i)
_twiddles[i] = cpx_t(+ sin((4*i-3*N)*d),
-s*cos((4*i-3*N)*d)); // pi/4*[5, 7)
for (; i < N; ++i)
_twiddles[i] = cpx_t(+ cos((4*i-4*N)*d),
+s*sin((4*i-4*N)*d)); // pi/4*[5, 8)
}
//factorize
//start factoring out 4's, then 2's, then 3,5,7,9,...
std::size_t n= _nfft;
@ -154,6 +173,7 @@ class kissfft
void transform_real( const scalar_t * const src,
cpx_t * const dst ) const
{
using std::acos; using std::exp;
const std::size_t N = _nfft;
if ( N == 0 )
return;
@ -166,9 +186,9 @@ class kissfft
dst[0].real() - dst[0].imag() );
// post processing for all the other k = 1, 2, ..., N-1
const scalar_t pi = std::acos( (scalar_t) -1);
const scalar_t pi = acos( (scalar_t) -1);
const scalar_t half_phi_inc = ( _inverse ? pi : -pi ) / N;
const cpx_t twiddle_mul = std::exp( cpx_t(0, half_phi_inc) );
const cpx_t twiddle_mul = exp( cpx_t(0, half_phi_inc) );
for ( std::size_t k = 1; 2*k < N; ++k )
{
const cpx_t w = (scalar_t)0.5 * cpx_t(