date and time created 85/08/21 11:17:55 by miriam

SCCS-vsn: old/libm/libm/atan.c 1.1

diff --git a/usr/src/old/libm/libm/atan.c b/usr/src/old/libm/libm/atan.c
new file mode 100644 (file)
index 0000000..cd0031f
--- /dev/null
+++ b/usr/src/old/libm/libm/atan.c
@@ -0,0 +1,67 @@
+/* 
+ * 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[] = "@(#)atan.c     1.1 (Berkeley) %G%";
+#endif not lint
+
+/* ATAN(X)
+ * RETURNS ARC TANGENT OF X
+ * DOUBLE PRECISION (IEEE DOUBLE 53 bits, VAX D FORMAT 56 bits)
+ * CODED IN C BY K.C. NG, 4/16/85, REVISED ON 6/10/85.
+ *
+ * Required kernel function:
+ *     atan2(y,x) 
+ *
+ * Method:                  
+ *     atan(x) = atan2(x,1.0). 
+ *
+ * Special case:
+ *     if x is NaN, return x itself.
+ *
+ * Accuracy:
+ * 1)  If atan2() uses machine PI, then
+ * 
+ *     atan(x) returns (PI/pi) * (the exact arc tangent of x) nearly rounded;
+ *     and PI is the exact pi rounded to machine precision (see atan2 for
+ *      details):
+ *
+ *     in decimal:
+ *             pi = 3.141592653589793 23846264338327 ..... 
+ *    53 bits   PI = 3.141592653589793 115997963 ..... ,
+ *    56 bits   PI = 3.141592653589793 227020265 ..... ,  
+ *
+ *     in hexadecimal:
+ *             pi = 3.243F6A8885A308D313198A2E....
+ *    53 bits   PI = 3.243F6A8885A30  =  2 * 1.921FB54442D18   error=.276ulps
+ *    56 bits   PI = 3.243F6A8885A308 =  4 * .C90FDAA22168C2    error=.206ulps
+ *     
+ *     In a test run with more than 200,000 random arguments on a VAX, the 
+ *     maximum observed error in ulps (units in the last place) was
+ *     0.86 ulps.      (comparing against (PI/pi)*(exact atan(x))).
+ *
+ * 2)  If atan2() uses true pi, then
+ *
+ *     atan(x) returns the exact atan(x) with error below about 2 ulps.
+ *
+ *     In a test run with more than 1,024,000 random arguments on a VAX, the 
+ *     maximum observed error in ulps (units in the last place) was
+ *     0.85 ulps.
+ */
+
+double atan(x)
+double x;
+{
+       double atan2(),one=1.0;
+       return(atan2(x,one));
+}