1 files changed, 177 insertions, 0 deletions
diff --git a/libm/float/i1f.c b/libm/float/i1f.c
new file mode 100644
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+/*							i1f.c
+ *
+ *	Modified Bessel function of order one
+ *
+ *
+ *
+ * SYNOPSIS:
+ *
+ * float x, y, i1f();
+ *
+ * y = i1f( x );
+ *
+ *
+ *
+ * DESCRIPTION:
+ *
+ * Returns modified Bessel function of order one of the
+ * argument.
+ *
+ * The function is defined as i1(x) = -i j1( ix ).
+ *
+ * The range is partitioned into the two intervals [0,8] and
+ * (8, infinity).  Chebyshev polynomial expansions are employed
+ * in each interval.
+ *
+ *
+ *
+ * ACCURACY:
+ *
+ *                      Relative error:
+ * arithmetic   domain     # trials      peak         rms
+ *    IEEE      0, 30       100000      1.5e-6      1.6e-7
+ *
+ *
+ */
+/*							i1ef.c
+ *
+ *	Modified Bessel function of order one,
+ *	exponentially scaled
+ *
+ *
+ *
+ * SYNOPSIS:
+ *
+ * float x, y, i1ef();
+ *
+ * y = i1ef( x );
+ *
+ *
+ *
+ * DESCRIPTION:
+ *
+ * Returns exponentially scaled modified Bessel function
+ * of order one of the argument.
+ *
+ * The function is defined as i1(x) = -i exp(-|x|) j1( ix ).
+ *
+ *
+ *
+ * ACCURACY:
+ *
+ *                      Relative error:
+ * arithmetic   domain     # trials      peak         rms
+ *    IEEE      0, 30       30000       1.5e-6      1.5e-7
+ * See i1().
+ *
+ */
+
+/*							i1.c 2		*/
+
+
+/*
+Cephes Math Library Release 2.0:  March, 1987
+Copyright 1985, 1987 by Stephen L. Moshier
+Direct inquiries to 30 Frost Street, Cambridge, MA 02140
+*/
+
+#include <math.h>
+
+/* Chebyshev coefficients for exp(-x) I1(x) / x
+ * in the interval [0,8].
+ *
+ * lim(x->0){ exp(-x) I1(x) / x } = 1/2.
+ */
+
+static float A[] =
+{
+ 9.38153738649577178388E-9f,
+-4.44505912879632808065E-8f,
+ 2.00329475355213526229E-7f,
+-8.56872026469545474066E-7f,
+ 3.47025130813767847674E-6f,
+-1.32731636560394358279E-5f,
+ 4.78156510755005422638E-5f,
+-1.61760815825896745588E-4f,
+ 5.12285956168575772895E-4f,
+-1.51357245063125314899E-3f,
+ 4.15642294431288815669E-3f,
+-1.05640848946261981558E-2f,
+ 2.47264490306265168283E-2f,
+-5.29459812080949914269E-2f,
+ 1.02643658689847095384E-1f,
+-1.76416518357834055153E-1f,
+ 2.52587186443633654823E-1f
+};
+
+
+/* Chebyshev coefficients for exp(-x) sqrt(x) I1(x)
+ * in the inverted interval [8,infinity].
+ *
+ * lim(x->inf){ exp(-x) sqrt(x) I1(x) } = 1/sqrt(2pi).
+ */
+
+static float B[] =
+{
+-3.83538038596423702205E-9f,
+-2.63146884688951950684E-8f,
+-2.51223623787020892529E-7f,
+-3.88256480887769039346E-6f,
+-1.10588938762623716291E-4f,
+-9.76109749136146840777E-3f,
+ 7.78576235018280120474E-1f
+};
+
+/*							i1.c	*/
+
+#define fabsf(x) ( (x) < 0 ? -(x) : (x) )
+
+#ifdef ANSIC
+float chbevlf(float, float *, int);
+float expf(float), sqrtf(float);
+#else
+float chbevlf(), expf(), sqrtf();
+#endif
+
+
+float i1f(float xx)
+{ 
+float x, y, z;
+
+x = xx;
+z = fabsf(x);
+if( z <= 8.0f )
+	{
+	y = 0.5f*z - 2.0f;
+	z = chbevlf( y, A, 17 ) * z * expf(z);
+	}
+else
+	{
+	z = expf(z) * chbevlf( 32.0f/z - 2.0f, B, 7 ) / sqrtf(z);
+	}
+if( x < 0.0f )
+	z = -z;
+return( z );
+}
+
+/*							i1e()	*/
+
+float i1ef( float xx )
+{ 
+float x, y, z;
+
+x = xx;
+z = fabsf(x);
+if( z <= 8.0f )
+	{
+	y = 0.5f*z - 2.0f;
+	z = chbevlf( y, A, 17 ) * z;
+	}
+else
+	{
+	z = chbevlf( 32.0f/z - 2.0f, B, 7 ) / sqrtf(z);
+	}
+if( x < 0.0f )
+	z = -z;
+return( z );
+}