add oversampler

oversampling/WDL/cmath/bessel_polynomial.h

@@ -0,0 +1,75 @@
+/*
+  bessel_polynomial.h
+  Copyright (C) 2011 and later Lubomir I. Ivanov (neolit123 [at] gmail)
+
+  This software is provided 'as-is', without any express or implied
+  warranty.  In no event will the authors be held liable for any damages
+  arising from the use of this software.
+
+  Permission is granted to anyone to use this software for any purpose,
+  including commercial applications, and to alter it and redistribute it
+  freely, subject to the following restrictions:
+
+  1. The origin of this software must not be misrepresented; you must not
+     claim that you wrote the original software. If you use this software
+     in a product, an acknowledgment in the product documentation would be
+     appreciated but is not required.
+  2. Altered source versions must be plainly marked as such, and must not be
+     misrepresented as being the original software.
+  3. This notice may not be removed or altered from any source distribution.
+*/
+
+/*
+  algorithm to calculate coefficients for a bessel polynomial from krall & fink
+  series.
+*/
+
+#ifndef _BESSEL_POLYNOMIAL_H_
+#define _BESSEL_POLYNOMIAL_H_
+
+#include "custom_math.h"
+#include "factorial.h"
+
+#ifdef _BESSEL_USE_INLINE_
+  #define _BESSEL_INLINE _CMATH_INLINE
+#else
+  #define _BESSEL_INLINE
+#endif
+
+#ifndef _CMATH_ANSI
+  #define _BESSEL_MAX_ORDER 10
+#else
+  #define _BESSEL_MAX_ORDER 3
+#endif
+
+/* return a coefficient */
+_BESSEL_INLINE cmath_std_int_t
+bessel_coefficient(const cmath_uint16_t k, const cmath_uint16_t n)
+{
+  register cmath_std_int_t c;
+  const cmath_uint16_t nmk = (cmath_uint16_t)(n - k);
+  c = factorial(2*n - k);
+  c /= (factorial(nmk)*factorial(k)) * (1 << nmk);
+  return c;
+}
+
+/* calculate all coefficients for n-th order polynomial */
+_BESSEL_INLINE
+void bessel_polynomial( cmath_std_int_t *coeff,
+                        const cmath_uint16_t order,
+                        const cmath_uint16_t reverse )
+{
+  register cmath_uint16_t i = (cmath_uint16_t)(order + 1);
+  if (reverse)
+  {
+    while (i--)
+      coeff[order-i] = bessel_coefficient(i, order);
+  }
+  else
+  {
+    while (i--)
+      coeff[i] = bessel_coefficient(i, order);
+  }
+}
+
+#endif /* _BESSEL_POLYNOMIAL_H */