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@@ -0,0 +1,171 @@
+//===========================================================================
+//
+//      k_tan.c
+//
+//      Part of the standard mathematical function library
+//
+//===========================================================================
+//####COPYRIGHTBEGIN####
+//
+// -------------------------------------------
+// The contents of this file are subject to the Cygnus eCos Public License
+// Version 1.0 (the "License"); you may not use this file except in
+// compliance with the License.  You may obtain a copy of the License at
+// http://sourceware.cygnus.com/ecos
+// 
+// Software distributed under the License is distributed on an "AS IS"
+// basis, WITHOUT WARRANTY OF ANY KIND, either express or implied.  See the
+// License for the specific language governing rights and limitations under
+// the License.
+// 
+// The Original Code is eCos - Embedded Cygnus Operating System, released
+// September 30, 1998.
+// 
+// The Initial Developer of the Original Code is Cygnus.  Portions created
+// by Cygnus are Copyright (C) 1998 Cygnus Solutions.  All Rights Reserved.
+// -------------------------------------------
+//
+//####COPYRIGHTEND####
+//===========================================================================
+//#####DESCRIPTIONBEGIN####
+//
+// Author(s):   jlarmour@cygnus.co.uk
+// Contributors:  jlarmour@cygnus.co.uk
+// Date:        1998-02-13
+// Purpose:     
+// Description: 
+// Usage:       
+//
+//####DESCRIPTIONEND####
+//
+//===========================================================================
+
+// CONFIGURATION
+
+#include <pkgconf/libm.h>   // Configuration header
+
+// Include the Math library?
+#ifdef CYGPKG_LIBM     
+
+// Derived from code with the following copyright
+
+
+/* @(#)k_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.
+ * ====================================================
+ */
+
+/* __kernel_tan( x, y, k )
+ * kernel tan function on [-pi/4, pi/4], pi/4 ~ 0.7854
+ * Input x is assumed to be bounded by ~pi/4 in magnitude.
+ * Input y is the tail of x.
+ * Input k indicates whether tan (if k=1) or 
+ * -1/tan (if k= -1) is returned.
+ *
+ * Algorithm
+ *      1. Since tan(-x) = -tan(x), we need only to consider positive x. 
+ *      2. if x < 2^-28 (hx<0x3e300000 0), return x with inexact if x!=0.
+ *      3. tan(x) is approximated by a odd polynomial of degree 27 on
+ *         [0,0.67434]
+ *                               3             27
+ *              tan(x) ~ x + T1*x + ... + T13*x
+ *         where
+ *      
+ *              |tan(x)         2     4            26   |     -59.2
+ *              |----- - (1+T1*x +T2*x +.... +T13*x    )| <= 2
+ *              |  x                                    | 
+ * 
+ *         Note: tan(x+y) = tan(x) + tan'(x)*y
+ *                        ~ tan(x) + (1+x*x)*y
+ *         Therefore, for better accuracy in computing tan(x+y), let 
+ *                   3      2      2       2       2
+ *              r = x *(T2+x *(T3+x *(...+x *(T12+x *T13))))
+ *         then
+ *                                  3    2
+ *              tan(x+y) = x + (T1*x + (x *(r+y)+y))
+ *
+ *      4. For x in [0.67434,pi/4],  let y = pi/4 - x, then
+ *              tan(x) = tan(pi/4-y) = (1-tan(y))/(1+tan(y))
+ *                     = 1 - 2*(tan(y) - (tan(y)^2)/(1+tan(y)))
+ */
+
+#include "mathincl/fdlibm.h"
+static const double 
+one   =  1.00000000000000000000e+00, /* 0x3FF00000, 0x00000000 */
+pio4  =  7.85398163397448278999e-01, /* 0x3FE921FB, 0x54442D18 */
+pio4lo=  3.06161699786838301793e-17, /* 0x3C81A626, 0x33145C07 */
+T[] =  {
+  3.33333333333334091986e-01, /* 0x3FD55555, 0x55555563 */
+  1.33333333333201242699e-01, /* 0x3FC11111, 0x1110FE7A */
+  5.39682539762260521377e-02, /* 0x3FABA1BA, 0x1BB341FE */
+  2.18694882948595424599e-02, /* 0x3F9664F4, 0x8406D637 */
+  8.86323982359930005737e-03, /* 0x3F8226E3, 0xE96E8493 */
+  3.59207910759131235356e-03, /* 0x3F6D6D22, 0xC9560328 */
+  1.45620945432529025516e-03, /* 0x3F57DBC8, 0xFEE08315 */
+  5.88041240820264096874e-04, /* 0x3F4344D8, 0xF2F26501 */
+  2.46463134818469906812e-04, /* 0x3F3026F7, 0x1A8D1068 */
+  7.81794442939557092300e-05, /* 0x3F147E88, 0xA03792A6 */
+  7.14072491382608190305e-05, /* 0x3F12B80F, 0x32F0A7E9 */
+ -1.85586374855275456654e-05, /* 0xBEF375CB, 0xDB605373 */
+  2.59073051863633712884e-05, /* 0x3EFB2A70, 0x74BF7AD4 */
+};
+
+        double __kernel_tan(double x, double y, int iy)
+{
+        double z,r,v,w,s;
+        int ix,hx;
+        hx = CYG_LIBM_HI(x);    /* high word of x */
+        ix = hx&0x7fffffff;     /* high word of |x| */
+        if(ix<0x3e300000)                       /* x < 2**-28 */
+            {if((int)x==0) {                    /* generate inexact */
+                if(((ix|CYG_LIBM_LO(x))|(iy+1))==0) return one/fabs(x);
+                else return (iy==1)? x: -one/x;
+            }
+            }
+        if(ix>=0x3FE59428) {                    /* |x|>=0.6744 */
+            if(hx<0) {x = -x; y = -y;}
+            z = pio4-x;
+            w = pio4lo-y;
+            x = z+w; y = 0.0;
+        }
+        z       =  x*x;
+        w       =  z*z;
+    /* Break x^5*(T[1]+x^2*T[2]+...) into
+     *    x^5(T[1]+x^4*T[3]+...+x^20*T[11]) +
+     *    x^5(x^2*(T[2]+x^4*T[4]+...+x^22*[T12]))
+     */
+        r = T[1]+w*(T[3]+w*(T[5]+w*(T[7]+w*(T[9]+w*T[11]))));
+        v = z*(T[2]+w*(T[4]+w*(T[6]+w*(T[8]+w*(T[10]+w*T[12])))));
+        s = z*x;
+        r = y + z*(s*(r+v)+y);
+        r += T[0]*s;
+        w = x+r;
+        if(ix>=0x3FE59428) {
+            v = (double)iy;
+            return (double)(1-((hx>>30)&2))*(v-2.0*(x-(w*w/(w+v)-r)));
+        }
+        if(iy==1) return w;
+        else {          /* if allow error up to 2 ulp, 
+                           simply return -1.0/(x+r) here */
+     /*  compute -1.0/(x+r) accurately */
+            double a,t;
+            z  = w;
+            CYG_LIBM_LO(z) = 0;
+            v  = r-(z - x);     /* z+v = r+x */
+            t = a  = -1.0/w;    /* a = -1.0/w */
+            CYG_LIBM_LO(t) = 0;
+            s  = 1.0+t*z;
+            return t+a*(s+t*v);
+        }
+}
+
+#endif // ifdef CYGPKG_LIBM     
+
+// EOF k_tan.c