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  #ifdef HAVE_CONFIG_H
  #include "config.h"
  #endif
  
  #include "SigProc_FIX.h"
  
  /* Apply sine window to signal vector.                                      */
  /* Window types:                                                            */
  /*    1 -> sine window from 0 to pi/2                                       */
  /*    2 -> sine window from pi/2 to pi                                      */
  /* Every other sample is linearly interpolated, for speed.                  */
  /* Window length must be between 16 and 120 (incl) and a multiple of 4.     */
  
  /* Matlab code for table:
     for k=16:9*4:16+2*9*4, fprintf(' %7.d,', -round(65536*pi ./ (k:4:k+8*4))); fprintf('\n'); end
  */
  static const opus_int16 freq_table_Q16[27] = {
          12111, 9804, 8235, 7100, 6239, 5565, 5022, 4575, 4202,
          3885, 3612, 3375, 3167, 2984, 2820, 2674, 2542, 2422,
          2313, 2214, 2123, 2038, 1961, 1889, 1822, 1760, 1702,
  };
  
  void silk_apply_sine_window(
          opus_int16 px_win[],           /* O    Pointer to windowed signal                                  */
          const opus_int16 px[],               /* I    Pointer to input signal                                     */
          const opus_int win_type,           /* I    Selects a window type                                       */
          const opus_int length              /* I    Window length, multiple of 4                                */
  ) {
      opus_int k, f_Q16, c_Q16;
      opus_int32 S0_Q16, S1_Q16;
  
      silk_assert(win_type == 1 || win_type == 2);
  
      /* Length must be in a range from 16 to 120 and a multiple of 4 */
      silk_assert(length >= 16 && length <= 120);
      silk_assert((length & 3) == 0);
  
      /* Frequency */
      k = (length >> 2) - 4;
      silk_assert(k >= 0 && k <= 26);
      f_Q16 = (opus_int) freq_table_Q16[k];
  
      /* Factor used for cosine approximation */
      c_Q16 = silk_SMULWB((opus_int32) f_Q16, -f_Q16);
      silk_assert(c_Q16 >= -32768);
  
      /* initialize state */
      if (win_type == 1) {
          /* start from 0 */
          S0_Q16 = 0;
          /* approximation of sin(f) */
          S1_Q16 = f_Q16 + silk_RSHIFT(length, 3);
      } else {
          /* start from 1 */
          S0_Q16 = ((opus_int32) 1 << 16);
          /* approximation of cos(f) */
          S1_Q16 = ((opus_int32) 1 << 16) + silk_RSHIFT(c_Q16, 1) + silk_RSHIFT(length, 4);
      }
  
      /* Uses the recursive equation:   sin(n*f) = 2 * cos(f) * sin((n-1)*f) - sin((n-2)*f)    */
      /* 4 samples at a time */
      for (k = 0; k < length; k += 4) {
          px_win[k] = (opus_int16) silk_SMULWB(silk_RSHIFT(S0_Q16 + S1_Q16, 1), px[k]);
          px_win[k + 1] = (opus_int16) silk_SMULWB(S1_Q16, px[k + 1]);
          S0_Q16 = silk_SMULWB(S1_Q16, c_Q16) + silk_LSHIFT(S1_Q16, 1) - S0_Q16 + 1;
          S0_Q16 = silk_min(S0_Q16, ((opus_int32) 1 << 16));
  
          px_win[k + 2] = (opus_int16) silk_SMULWB(silk_RSHIFT(S0_Q16 + S1_Q16, 1), px[k + 2]);
          px_win[k + 3] = (opus_int16) silk_SMULWB(S0_Q16, px[k + 3]);
          S1_Q16 = silk_SMULWB(S0_Q16, c_Q16) + silk_LSHIFT(S0_Q16, 1) - S1_Q16;
          S1_Q16 = silk_min(S1_Q16, ((opus_int32) 1 << 16));
      }
  }
  