add directory gnu

gnu/glibc/glibc-1.03/math/bsd/common_source/atan.c

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+/*
+ * Copyright (c) 1985 Regents of the University of California.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms are permitted provided
+ * that: (1) source distributions retain this entire copyright notice and
+ * comment, and (2) distributions including binaries display the following
+ * acknowledgement:  ``This product includes software developed by the
+ * University of California, Berkeley and its contributors'' in the
+ * documentation or other materials provided with the distribution and in
+ * all advertising materials mentioning features or use of this software.
+ * Neither the name of the University nor the names of its contributors may
+ * be used to endorse or promote products derived from this software without
+ * specific prior written permission.
+ * THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR IMPLIED
+ * WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
+ */
+
+#ifndef lint
+static char sccsid[] = "@(#)atan.c	5.5 (Berkeley) 10/9/90";
+#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));
+}