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[ctsim.git] / libctsim / convolve.cpp

diff --git a/libctsim/convolve.cpp b/libctsim/convolve.cpp
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--- a/libctsim/convolve.cpp
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-/*****************************************************************************
-** FILE IDENTIFICATION
-**
-**     Name:           Convolve.c              Convolution functions
-**     Date Started:   13 Mar 86
-**
-**  This is part of the CTSim program
-**  Copyright (C) 1983-2000 Kevin Rosenberg
-**
-**  This program is free software; you can redistribute it and/or modify
-**  it under the terms of the GNU General Public License (version 2) as
-**  published by the Free Software Foundation.
-**
-**  This program 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 General Public License for more details.
-**
-**  You should have received a copy of the GNU General Public License
-**  along with this program; if not, write to the Free Software
-**  Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
-******************************************************************************/
-
-#include "ct.h"
-
-
-/* NAME
- *    convolve                 Discrete convolution of two functions
- *
- * SYNOPSIS
- *    r = convolve (f1, f2, dx, n, np, func_type)
- *    double r                 Convolved result
- *    double f1[], f2[]                Functions to be convolved
- *    double dx                        Difference between successive x values
- *    int n                    Array index to center convolution about
- *    int np                   Number of points in f1 array
- *    int func_type            EVEN or ODD or EVEN_AND_ODD function f2
- *
- * NOTES
- *    f1 is the projection data, its indices range from 0 to np - 1.
- *    The index for f2, the filter, ranges from -(np-1) to (np-1).
- *    There are 3 ways to handle the negative vertices of f2:
- *     1. If we know f2 is an EVEN function, then f2[-n] = f2[n].
- *        All filters used in reconstruction are even.
- *      2. If we know f2 is an ODD function, then f2[-n] = -f2[n] 
- *      3. If f2 is both ODD AND EVEN, then we must store the value of f2
- *        for negative indices.  Since f2 must range from -(np-1) to (np-1),
- *        if we add (np - 1) to f2's array index, then f2's index will
- *        range from 0 to 2 * (np - 1), and the origin, x = 0, will be
- *        stored at f2[np-1].
- */
-
-double 
-convolve (const double f1[], const double f2[], const double dx, const int n, const int np, const FunctionSymmetry func_type)
-{
-  double sum = 0.0;
-
-  if (func_type == FUNC_BOTH) {
-#if UNOPTIMIZED_CONVOLUTION
-    for (int i = 0; i < np; i++)
-      sum += f1[i] * f2[n - i + (np - 1)];
-#else
-    f2 += n + (np - 1);
-    for (int i = 0; i < np; i++)
-      sum += *f1++ * *f2--;
-#endif
-  }  else if (func_type == FUNC_EVEN) {
-    for (int i = 0; i < np; i++) {
-      int k = abs (n - i);
-      sum += f1[i] * f2[k];
-    }
-  } else if (func_type == FUNC_ODD) {
-    for (int i = 0; i < np; i++) {
-      int k = n - i;
-      if (k < 0)
-       sum -= f1[i] * f2[k];
-      else
-       sum += f1[i] * f2[k];
-    }
-  } else
-    sys_error (ERR_WARNING, "Illegal function type %d [convolve]", func_type);
-
-  return (sum * dx);
-}