1 files changed, 160 insertions, 0 deletions
diff --git a/libm/float/i0f.c b/libm/float/i0f.c
new file mode 100644
index 000000000..bb62cf60a
--- /dev/null
+++ b/libm/float/i0f.c
@@ -0,0 +1,160 @@
+/*							i0f.c
+ *
+ *	Modified Bessel function of order zero
+ *
+ *
+ *
+ * SYNOPSIS:
+ *
+ * float x, y, i0();
+ *
+ * y = i0f( x );
+ *
+ *
+ *
+ * DESCRIPTION:
+ *
+ * Returns modified Bessel function of order zero of the
+ * argument.
+ *
+ * The function is defined as i0(x) = j0( 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      4.0e-7      7.9e-8
+ *
+ */
+/*							i0ef.c
+ *
+ *	Modified Bessel function of order zero,
+ *	exponentially scaled
+ *
+ *
+ *
+ * SYNOPSIS:
+ *
+ * float x, y, i0ef();
+ *
+ * y = i0ef( x );
+ *
+ *
+ *
+ * DESCRIPTION:
+ *
+ * Returns exponentially scaled modified Bessel function
+ * of order zero of the argument.
+ *
+ * The function is defined as i0e(x) = exp(-|x|) j0( ix ).
+ *
+ *
+ *
+ * ACCURACY:
+ *
+ *                      Relative error:
+ * arithmetic   domain     # trials      peak         rms
+ *    IEEE      0,30        100000      3.7e-7      7.0e-8
+ * See i0f().
+ *
+ */
+
+/*							i0.c		*/
+
+
+/*
+Cephes Math Library Release 2.2:  June, 1992
+Copyright 1984, 1987, 1992 by Stephen L. Moshier
+Direct inquiries to 30 Frost Street, Cambridge, MA 02140
+*/
+
+#include <math.h>
+
+/* Chebyshev coefficients for exp(-x) I0(x)
+ * in the interval [0,8].
+ *
+ * lim(x->0){ exp(-x) I0(x) } = 1.
+ */
+
+static float A[] =
+{
+-1.30002500998624804212E-8f,
+ 6.04699502254191894932E-8f,
+-2.67079385394061173391E-7f,
+ 1.11738753912010371815E-6f,
+-4.41673835845875056359E-6f,
+ 1.64484480707288970893E-5f,
+-5.75419501008210370398E-5f,
+ 1.88502885095841655729E-4f,
+-5.76375574538582365885E-4f,
+ 1.63947561694133579842E-3f,
+-4.32430999505057594430E-3f,
+ 1.05464603945949983183E-2f,
+-2.37374148058994688156E-2f,
+ 4.93052842396707084878E-2f,
+-9.49010970480476444210E-2f,
+ 1.71620901522208775349E-1f,
+-3.04682672343198398683E-1f,
+ 6.76795274409476084995E-1f
+};
+
+
+/* Chebyshev coefficients for exp(-x) sqrt(x) I0(x)
+ * in the inverted interval [8,infinity].
+ *
+ * lim(x->inf){ exp(-x) sqrt(x) I0(x) } = 1/sqrt(2pi).
+ */
+
+static float B[] =
+{
+ 3.39623202570838634515E-9f,
+ 2.26666899049817806459E-8f,
+ 2.04891858946906374183E-7f,
+ 2.89137052083475648297E-6f,
+ 6.88975834691682398426E-5f,
+ 3.36911647825569408990E-3f,
+ 8.04490411014108831608E-1f
+};
+
+ 
+float chbevlf(float, float *, int), expf(float), sqrtf(float);
+
+float i0f( float x )
+{
+float y;
+
+if( x < 0 )
+	x = -x;
+if( x <= 8.0f )
+	{
+	y = 0.5f*x - 2.0f;
+	return( expf(x) * chbevlf( y, A, 18 ) );
+	}
+
+return(  expf(x) * chbevlf( 32.0f/x - 2.0f, B, 7 ) / sqrtf(x) );
+}
+
+
+
+float chbevlf(float, float *, int), expf(float), sqrtf(float);
+
+float i0ef( float x )
+{
+float y;
+
+if( x < 0 )
+	x = -x;
+if( x <= 8.0f )
+	{
+	y = 0.5f*x - 2.0f;
+	return( chbevlf( y, A, 18 ) );
+	}
+
+return(  chbevlf( 32.0f/x - 2.0f, B, 7 ) / sqrtf(x) );
+}