date and time created 85/09/06 17:52:42 by zliu

SCCS-vsn: lib/libm/common_source/atanh.c 1.1

diff --git a/usr/src/lib/libm/common_source/atanh.c b/usr/src/lib/libm/common_source/atanh.c
new file mode 100644 (file)
index 0000000..42b1414
--- /dev/null
+++ b/usr/src/lib/libm/common_source/atanh.c
@@ -0,0 +1,62 @@
+/* 
+ * Copyright (c) 1985 Regents of the University of California.
+ * 
+ * Use and reproduction of this software are granted  in  accordance  with
+ * the terms and conditions specified in  the  Berkeley  Software  License
+ * Agreement (in particular, this entails acknowledgement of the programs'
+ * source, and inclusion of this notice) with the additional understanding
+ * that  all  recipients  should regard themselves as participants  in  an
+ * ongoing  research  project and hence should  feel  obligated  to report
+ * their  experiences (good or bad) with these elementary function  codes,
+ * using "sendbug 4bsd-bugs@BERKELEY", to the authors.
+ */
+
+#ifndef lint
+static char sccsid[] = "@(#)atanh.c    1.1 (ELEFUNT) %G%";
+#endif not lint
+
+/* ATANH(X)
+ * RETURN THE HYPERBOLIC ARC TANGENT OF X
+ * DOUBLE PRECISION (VAX D format 56 bits, IEEE DOUBLE 53 BITS)
+ * CODED IN C BY K.C. NG, 1/8/85; 
+ * REVISED BY K.C. NG on 2/7/85, 3/7/85, 8/18/85.
+ *
+ * Required kernel function:
+ *     log1p(x)        ...return log(1+x)
+ *
+ * Method :
+ *     Return 
+ *                          1              2x                          x
+ *             atanh(x) = --- * log(1 + -------) = 0.5 * log1p(2 * --------)
+ *                          2             1 - x                      1 - x
+ *
+ * Special cases:
+ *     atanh(x) is NaN if |x| > 1 with signal;
+ *     atanh(NaN) is that NaN with no signal;
+ *     atanh(+-1) is +-INF with signal.
+ *
+ * Accuracy:
+ *     atanh(x) returns the exact hyperbolic arc tangent of x nearly rounded.
+ *     In a test run with 512,000 random arguments on a VAX, the maximum
+ *     observed error was 1.87 ulps (units in the last place) at
+ *     x= -3.8962076028810414000e-03.
+ */
+#ifdef VAX
+#include <errno.h>
+#endif
+
+double atanh(x)
+double x;
+{
+       double copysign(),log1p(),z;
+       z = copysign(0.5,x);
+       x = copysign(x,1.0);
+#ifdef VAX
+       if (x == 1.0) {
+           extern double infnan();
+           return(copysign(1.0,z)*infnan(ERANGE));     /* sign(x)*INF */
+       }
+#endif
+       x = x/(1.0-x);
+       return( z*log1p(x+x) );
+}