src/rate_poly_fir.h

   1 /* Effect: change sample rate     Copyright (c) 2008 robs@users.sourceforge.net
   2  *
   3  * This library is free software; you can redistribute it and/or modify it
   4  * under the terms of the GNU Lesser General Public License as published by
   5  * the Free Software Foundation; either version 2.1 of the License, or (at
   6  * your option) any later version.
   7  *
   8  * This library is distributed in the hope that it will be useful, but
   9  * WITHOUT ANY WARRANTY; without even the implied warranty of
  10  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser
  11  * General Public License for more details.
  12  *
  13  * You should have received a copy of the GNU Lesser General Public License
  14  * along with this library; if not, write to the Free Software Foundation,
  15  * Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
  16  */
  17
  18 /* Up-sample by step in (0,1) using a poly-phase FIR with length LEN.*/
  19 /* Input must be preceded by LEN >> 1 samples. */
  20 /* Input must be followed by (LEN-1) >> 1 samples. */
  21
  22 #define a (coef(p->shared->poly_fir_coefs, COEF_INTERP, FIR_LENGTH, phase, 0,j))
  23 #define b (coef(p->shared->poly_fir_coefs, COEF_INTERP, FIR_LENGTH, phase, 1,j))
  24 #define c (coef(p->shared->poly_fir_coefs, COEF_INTERP, FIR_LENGTH, phase, 2,j))
  25 #define d (coef(p->shared->poly_fir_coefs, COEF_INTERP, FIR_LENGTH, phase, 3,j))
  26 #if COEF_INTERP == 0
  27   #define _ sum += a *at[j], ++j;
  28 #elif COEF_INTERP == 1
  29   #define _ sum += (b *x + a)*at[j], ++j;
  30 #elif COEF_INTERP == 2
  31   #define _ sum += ((c *x + b)*x + a)*at[j], ++j;
  32 #elif COEF_INTERP == 3
  33   #define _ sum += (((d*x + c)*x + b)*x + a)*at[j], ++j;
  34 #else
  35   #error COEF_INTERP
  36 #endif
  37
  38 static void FUNCTION(stage_t * p, fifo_t * output_fifo)
  39 {
  40   sample_t const * input = stage_read_p(p);
  41   int i, num_in = stage_occupancy(p), max_num_out = 1 + num_in*p->out_in_ratio;
  42   sample_t * output = fifo_reserve(output_fifo, max_num_out);
  43
  44   for (i = 0; p->at.parts.integer < num_in; ++i, p->at.all += p->step.all) {
  45     sample_t const * at = input + p->at.parts.integer;
  46     uint32_t fraction = p->at.parts.fraction;
  47     int phase = fraction >> (32 - PHASE_BITS); /* high-order bits */
  48 #if COEF_INTERP > 0              /* low-order bits, scaled to [0,1) */
  49     sample_t x = (sample_t) (fraction << PHASE_BITS) * (1 / MULT32);
  50 #endif
  51     sample_t sum = 0;
  52     int j = 0;
  53     CONVOLVE
  54     assert(j == FIR_LENGTH);
  55     output[i] = sum;
  56   }
  57   assert(max_num_out - i >= 0);
  58   fifo_trim_by(output_fifo, max_num_out - i);
  59   fifo_read(&p->fifo, p->at.parts.integer, NULL);
  60   p->at.parts.integer = 0;
  61 }
  62
  63 #undef _
  64 #undef a
  65 #undef b
  66 #undef c
  67 #undef d
  68 #undef COEF_INTERP
  69 #undef CONVOLVE
  70 #undef FIR_LENGTH
  71 #undef FUNCTION
  72 #undef PHASE_BITS