add fdlibm

git-svn-id: http://svn2.nishi.boats/svn/milsko/trunk@557 b9cfdab3-6d41-4d17-bbe4-086880011989

external/fdlibm/s_tan.c

@@ -0,0 +1,67 @@
+
+/* @(#)s_tan.c 1.3 95/01/18 */
+/*
+ * ====================================================
+ * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
+ *
+ * Developed at SunSoft, a Sun Microsystems, Inc. business.
+ * Permission to use, copy, modify, and distribute this
+ * software is freely granted, provided that this notice
+ * is preserved.
+ * ====================================================
+ */
+
+/* tan(x)
+ * Return tangent function of x.
+ *
+ * kernel function:
+ *	__fdlibm_kernel_tan		... tangent function on [-pi/4,pi/4]
+ *	__fdlibm_kernel_rem_pio2	... argument reduction routine
+ *
+ * Method.
+ *      Let S,C and T denote the sin, cos and tan respectively on
+ *	[-PI/4, +PI/4]. Reduce the argument x to y1+y2 = x-k*pi/2
+ *	in [-pi/4 , +pi/4], and let n = k mod 4.
+ *	We have
+ *
+ *          n        sin(x)      cos(x)        tan(x)
+ *     ----------------------------------------------------------
+ *	    0	       S	   C		 T
+ *	    1	       C	  -S		-1/T
+ *	    2	      -S	  -C		 T
+ *	    3	      -C	   S		-1/T
+ *     ----------------------------------------------------------
+ *
+ * Special cases:
+ *      Let trig be any of sin, cos, or tan.
+ *      trig(+-INF)  is NaN, with signals;
+ *      trig(NaN)    is that NaN;
+ *
+ * Accuracy:
+ *	TRIG(x) returns trig(x) nearly rounded
+ */
+
+#include "math.h"
+
+double tan(double x) {
+	double y[2], z = 0.0;
+	int    n, ix;
+
+	/* High word of x. */
+	ix = __HI(x);
+
+	/* |x| ~< pi/4 */
+	ix &= 0x7fffffff;
+	if(ix <= 0x3fe921fb) return __fdlibm_kernel_tan(x, z, 1);
+
+	/* tan(Inf or NaN) is NaN */
+	else if(ix >= 0x7ff00000)
+		return x - x; /* NaN */
+
+	/* argument reduction needed */
+	else {
+		n = __fdlibm_rem_pio2(x, y);
+		return __fdlibm_kernel_tan(y[0], y[1], 1 - ((n & 1) << 1)); /*   1 -- n even
+								    -1 -- n odd */
+	}
+}