Add DSP code to filter data, allowing for integration/differentiation

[fw/altos] / ao-tools / lib / chbevl.c

diff --git a/ao-tools/lib/chbevl.c b/ao-tools/lib/chbevl.c
new file mode 100644 (file)
index 0000000..2289241
--- /dev/null
+++ b/ao-tools/lib/chbevl.c
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+/*                                                     chbevl.c
+ *
+ *     Evaluate Chebyshev series
+ *
+ *
+ *
+ * SYNOPSIS:
+ *
+ * int N;
+ * double x, y, coef[N], chebevl();
+ *
+ * y = chbevl( x, coef, N );
+ *
+ *
+ *
+ * DESCRIPTION:
+ *
+ * Evaluates the series
+ *
+ *        N-1
+ *         - '
+ *  y  =   >   coef[i] T (x/2)
+ *         -            i
+ *        i=0
+ *
+ * of Chebyshev polynomials Ti at argument x/2.
+ *
+ * Coefficients are stored in reverse order, i.e. the zero
+ * order term is last in the array.  Note N is the number of
+ * coefficients, not the order.
+ *
+ * If coefficients are for the interval a to b, x must
+ * have been transformed to x -> 2(2x - b - a)/(b-a) before
+ * entering the routine.  This maps x from (a, b) to (-1, 1),
+ * over which the Chebyshev polynomials are defined.
+ *
+ * If the coefficients are for the inverted interval, in
+ * which (a, b) is mapped to (1/b, 1/a), the transformation
+ * required is x -> 2(2ab/x - b - a)/(b-a).  If b is infinity,
+ * this becomes x -> 4a/x - 1.
+ *
+ *
+ *
+ * SPEED:
+ *
+ * Taking advantage of the recurrence properties of the
+ * Chebyshev polynomials, the routine requires one more
+ * addition per loop than evaluating a nested polynomial of
+ * the same degree.
+ *
+ */
+\f/*                                                    chbevl.c        */
+
+/*
+Cephes Math Library Release 2.0:  April, 1987
+Copyright 1985, 1987 by Stephen L. Moshier
+Direct inquiries to 30 Frost Street, Cambridge, MA 02140
+*/
+
+#include "cephes.h"
+
+double chbevl(double x,void* array,int n )
+{
+double b0, b1, b2, *p;
+int i;
+
+p = (double *) array;
+b0 = *p++;
+b1 = 0.0;
+i = n - 1;
+
+do
+       {
+       b2 = b1;
+       b1 = b0;
+       b0 = x * b1  -  b2  + *p++;
+       }
+while( --i );
+
+return( 0.5*(b0-b2) );
+}