From 1077fa4d772832f77a677ce7fb7c2d513b959e3f Mon Sep 17 00:00:00 2001
From: Eric Andersen <andersen@codepoet.org>
Date: Thu, 10 May 2001 00:40:28 +0000
Subject: uClibc now has a math library.  muahahahaha!  -Erik

---
 libm/double/iv.c | 116 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 116 insertions(+)
 create mode 100644 libm/double/iv.c

(limited to 'libm/double/iv.c')

diff --git a/libm/double/iv.c b/libm/double/iv.c
new file mode 100644
index 000000000..ec0e96244
--- /dev/null
+++ b/libm/double/iv.c
@@ -0,0 +1,116 @@
+/*							iv.c
+ *
+ *	Modified Bessel function of noninteger order
+ *
+ *
+ *
+ * SYNOPSIS:
+ *
+ * double v, x, y, iv();
+ *
+ * y = iv( v, x );
+ *
+ *
+ *
+ * DESCRIPTION:
+ *
+ * Returns modified Bessel function of order v of the
+ * argument.  If x is negative, v must be integer valued.
+ *
+ * The function is defined as Iv(x) = Jv( ix ).  It is
+ * here computed in terms of the confluent hypergeometric
+ * function, according to the formula
+ *
+ *              v  -x
+ * Iv(x) = (x/2)  e   hyperg( v+0.5, 2v+1, 2x ) / gamma(v+1)
+ *
+ * If v is a negative integer, then v is replaced by -v.
+ *
+ *
+ * ACCURACY:
+ *
+ * Tested at random points (v, x), with v between 0 and
+ * 30, x between 0 and 28.
+ *                      Relative error:
+ * arithmetic   domain     # trials      peak         rms
+ *    DEC       0,30          2000      3.1e-15     5.4e-16
+ *    IEEE      0,30         10000      1.7e-14     2.7e-15
+ *
+ * Accuracy is diminished if v is near a negative integer.
+ *
+ * See also hyperg.c.
+ *
+ */
+/*							iv.c	*/
+/*	Modified Bessel function of noninteger order		*/
+/* If x < 0, then v must be an integer. */
+
+
+/*
+Cephes Math Library Release 2.8:  June, 2000
+Copyright 1984, 1987, 1988, 2000 by Stephen L. Moshier
+*/
+
+
+#include <math.h>
+#ifdef ANSIPROT
+extern double hyperg ( double, double, double );
+extern double exp ( double );
+extern double gamma ( double );
+extern double log ( double );
+extern double fabs ( double );
+extern double floor ( double );
+#else
+double hyperg(), exp(), gamma(), log(), fabs(), floor();
+#endif
+extern double MACHEP, MAXNUM;
+
+double iv( v, x )
+double v, x;
+{
+int sign;
+double t, ax;
+
+/* If v is a negative integer, invoke symmetry */
+t = floor(v);
+if( v < 0.0 )
+	{
+	if( t == v )
+		{
+		v = -v;	/* symmetry */
+		t = -t;
+		}
+	}
+/* If x is negative, require v to be an integer */
+sign = 1;
+if( x < 0.0 )
+	{
+	if( t != v )
+		{
+		mtherr( "iv", DOMAIN );
+		return( 0.0 );
+		}
+	if( v != 2.0 * floor(v/2.0) )
+		sign = -1;
+	}
+
+/* Avoid logarithm singularity */
+if( x == 0.0 )
+	{
+	if( v == 0.0 )
+		return( 1.0 );
+	if( v < 0.0 )
+		{
+		mtherr( "iv", OVERFLOW );
+		return( MAXNUM );
+		}
+	else
+		return( 0.0 );
+	}
+
+ax = fabs(x);
+t = v * log( 0.5 * ax )  -  x;
+t = sign * exp(t) / gamma( v + 1.0 );
+ax = v + 0.5;
+return( t * hyperg( ax,  2.0 * ax,  2.0 * x ) );
+}
-- 
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