1 files changed, 76 insertions, 0 deletions
diff --git a/libm/s_tan.c b/libm/s_tan.c
new file mode 100644
index 000000000..7c72bf234
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+/* @(#)s_tan.c 5.1 93/09/24 */
+/*
+ * ====================================================
+ * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
+ *
+ * Developed at SunPro, a Sun Microsystems, Inc. business.
+ * Permission to use, copy, modify, and distribute this
+ * software is freely granted, provided that this notice 
+ * is preserved.
+ * ====================================================
+ */
+
+#if defined(LIBM_SCCS) && !defined(lint)
+static char rcsid[] = "$NetBSD: s_tan.c,v 1.7 1995/05/10 20:48:18 jtc Exp $";
+#endif
+
+/* tan(x)
+ * Return tangent function of x.
+ *
+ * kernel function:
+ *	__kernel_tan		... tangent function on [-pi/4,pi/4]
+ *	__ieee754_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"
+#include "math_private.h"
+
+#ifdef __STDC__
+	double tan(double x)
+#else
+	double tan(x)
+	double x;
+#endif
+{
+	double y[2],z=0.0;
+	int32_t n, ix;
+
+    /* High word of x. */
+	GET_HIGH_WORD(ix,x);
+
+    /* |x| ~< pi/4 */
+	ix &= 0x7fffffff;
+	if(ix <= 0x3fe921fb) return __kernel_tan(x,z,1);
+
+    /* tan(Inf or NaN) is NaN */
+	else if (ix>=0x7ff00000) return x-x;		/* NaN */
+
+    /* argument reduction needed */
+	else {
+	    n = __ieee754_rem_pio2(x,y);
+	    return __kernel_tan(y[0],y[1],1-((n&1)<<1)); /*   1 -- n even
+							-1 -- n odd */
+	}
+}