diff --git a/libao2/remez.c b/libao2/remez.c new file mode 100644 index 0000000000..afdce2c088 --- /dev/null +++ b/libao2/remez.c @@ -0,0 +1,704 @@ +/************************************************************************** + * Parks-McClellan algorithm for FIR filter design (C version) + *------------------------------------------------- + * Copyright (c) 1995,1998 Jake Janovetz (janovetz@uiuc.edu) + * + * This library is free software; you can redistribute it and/or + * modify it under the terms of the GNU Library General Public + * License as published by the Free Software Foundation; either + * version 2 of the License, or (at your option) any later version. + * + * This library is distributed in the hope that it will be useful, + * but WITHOUT ANY WARRANTY; without even the implied warranty of + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU + * Library General Public License for more details. + * + * You should have received a copy of the GNU Library General Public + * License along with this library; if not, write to the Free + * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA + * + *************************************************************************/ + + +#include "remez.h" +#include + +/******************* + * CreateDenseGrid + *================= + * Creates the dense grid of frequencies from the specified bands. + * Also creates the Desired Frequency Response function (D[]) and + * the Weight function (W[]) on that dense grid + * + * + * INPUT: + * ------ + * int r - 1/2 the number of filter coefficients + * int numtaps - Number of taps in the resulting filter + * int numband - Number of bands in user specification + * double bands[] - User-specified band edges [2*numband] + * double des[] - Desired response per band [numband] + * double weight[] - Weight per band [numband] + * int symmetry - Symmetry of filter - used for grid check + * + * OUTPUT: + * ------- + * int gridsize - Number of elements in the dense frequency grid + * double Grid[] - Frequencies (0 to 0.5) on the dense grid [gridsize] + * double D[] - Desired response on the dense grid [gridsize] + * double W[] - Weight function on the dense grid [gridsize] + *******************/ + +void CreateDenseGrid(int r, int numtaps, int numband, double bands[], + double des[], double weight[], int *gridsize, + double Grid[], double D[], double W[], + int symmetry) +{ + int i, j, k, band; + double delf, lowf, highf; + + delf = 0.5/(GRIDDENSITY*r); + +/* + * For differentiator, hilbert, + * symmetry is odd and Grid[0] = max(delf, band[0]) + */ + + if ((symmetry == NEGATIVE) && (delf > bands[0])) + bands[0] = delf; + + j=0; + for (band=0; band < numband; band++) + { + Grid[j] = bands[2*band]; + lowf = bands[2*band]; + highf = bands[2*band + 1]; + k = (int)((highf - lowf)/delf + 0.5); /* .5 for rounding */ + for (i=0; i (0.5 - delf)) && + (numtaps % 2)) + { + Grid[*gridsize-1] = 0.5-delf; + } +} + + +/******************** + * InitialGuess + *============== + * Places Extremal Frequencies evenly throughout the dense grid. + * + * + * INPUT: + * ------ + * int r - 1/2 the number of filter coefficients + * int gridsize - Number of elements in the dense frequency grid + * + * OUTPUT: + * ------- + * int Ext[] - Extremal indexes to dense frequency grid [r+1] + ********************/ + +void InitialGuess(int r, int Ext[], int gridsize) +{ + int i; + + for (i=0; i<=r; i++) + Ext[i] = i * (gridsize-1) / r; +} + + +/*********************** + * CalcParms + *=========== + * + * + * INPUT: + * ------ + * int r - 1/2 the number of filter coefficients + * int Ext[] - Extremal indexes to dense frequency grid [r+1] + * double Grid[] - Frequencies (0 to 0.5) on the dense grid [gridsize] + * double D[] - Desired response on the dense grid [gridsize] + * double W[] - Weight function on the dense grid [gridsize] + * + * OUTPUT: + * ------- + * double ad[] - 'b' in Oppenheim & Schafer [r+1] + * double x[] - [r+1] + * double y[] - 'C' in Oppenheim & Schafer [r+1] + ***********************/ + +void CalcParms(int r, int Ext[], double Grid[], double D[], double W[], + double ad[], double x[], double y[]) +{ + int i, j, k, ld; + double sign, xi, delta, denom, numer; + +/* + * Find x[] + */ + for (i=0; i<=r; i++) + x[i] = cos(Pi2 * Grid[Ext[i]]); + +/* + * Calculate ad[] - Oppenheim & Schafer eq 7.132 + */ + ld = (r-1)/15 + 1; /* Skips around to avoid round errors */ + for (i=0; i<=r; i++) + { + denom = 1.0; + xi = x[i]; + for (j=0; j0.0) && (E[0]>E[1])) || + ((E[0]<0.0) && (E[0]=E[i-1]) && (E[i]>E[i+1]) && (E[i]>0.0)) || + ((E[i]<=E[i-1]) && (E[i]0.0) && (E[j]>E[j-1])) || + ((E[j]<0.0) && (E[j] 0) + { + if (E[foundExt[0]] > 0.0) + up = 1; /* first one is a maxima */ + else + up = 0; /* first one is a minima */ + + l=0; + alt = 1; + for (j=1; j 0.0)) + up = 1; /* switch to a maxima */ + else + { + alt = 0; + break; /* Ooops, found two non-alternating */ + } /* extrema. Delete smallest of them */ + } /* if the loop finishes, all extrema are alternating */ + +/* + * If there's only one extremal and all are alternating, + * delete the smallest of the first/last extremals. + */ + if ((alt) && (extra == 1)) + { + if (fabs(E[foundExt[k-1]]) < fabs(E[foundExt[0]])) + l = foundExt[k-1]; /* Delete last extremal */ + else + l = foundExt[0]; /* Delete first extremal */ + } + + for (j=l; j max) + max = current; + } + if (((max-min)/max) < 0.0001) + return 1; + return 0; +} + +/******************** + * remez + *======= + * Calculates the optimal (in the Chebyshev/minimax sense) + * FIR filter impulse response given a set of band edges, + * the desired reponse on those bands, and the weight given to + * the error in those bands. + * + * INPUT: + * ------ + * int numtaps - Number of filter coefficients + * int numband - Number of bands in filter specification + * double bands[] - User-specified band edges [2 * numband] + * double des[] - User-specified band responses [numband] + * double weight[] - User-specified error weights [numband] + * int type - Type of filter + * + * OUTPUT: + * ------- + * double h[] - Impulse response of final filter [numtaps] + ********************/ + +void remez(double h[], int numtaps, + int numband, double bands[], double des[], double weight[], + int type) +{ + double *Grid, *W, *D, *E; + int i, iter, gridsize, r, *Ext; + double *taps, c; + double *x, *y, *ad; + int symmetry; + + if (type == BANDPASS) + symmetry = POSITIVE; + else + symmetry = NEGATIVE; + + r = numtaps/2; /* number of extrema */ + if ((numtaps%2) && (symmetry == POSITIVE)) + r++; + +/* + * Predict dense grid size in advance for memory allocation + * .5 is so we round up, not truncate + */ + gridsize = 0; + for (i=0; i 0.0001) + W[i] = W[i]/Grid[i]; + } + } + +/* + * For odd or Negative symmetry filters, alter the + * D[] and W[] according to Parks McClellan + */ + if (symmetry == POSITIVE) + { + if (numtaps % 2 == 0) + { + for (i=0; i