Function fill_first_half

numpy/fft/_pocketfft.c:164–179

  }

NOINLINE static void fill_first_half(size_t n, double * restrict res)
  {
  size_t half = n>>1;
  if ((n&3)==0)
    for (size_t i=0; i<half; i+=2)
      {
      res[i+half]   = -res[i+1];
      res[i+half+1] =  res[i  ];
      }
  else
    for (size_t i=2, j=2*half-2; i<half; i+=2, j-=2)
      {
      res[j  ] = -res[i  ];
      res[j+1] =  res[i+1];
      }
  }

NOINLINE static void fill_second_half(size_t n, double * restrict res)
  {