1 //===========================================================================
5 // Part of the standard mathematical function library
7 //===========================================================================
8 //####ECOSGPLCOPYRIGHTBEGIN####
9 // -------------------------------------------
10 // This file is part of eCos, the Embedded Configurable Operating System.
11 // Copyright (C) 1998, 1999, 2000, 2001, 2002 Red Hat, Inc.
13 // eCos is free software; you can redistribute it and/or modify it under
14 // the terms of the GNU General Public License as published by the Free
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17 // eCos is distributed in the hope that it will be useful, but WITHOUT ANY
18 // WARRANTY; without even the implied warranty of MERCHANTABILITY or
19 // FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
22 // You should have received a copy of the GNU General Public License along
23 // with eCos; if not, write to the Free Software Foundation, Inc.,
24 // 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA.
26 // As a special exception, if other files instantiate templates or use macros
27 // or inline functions from this file, or you compile this file and link it
28 // with other works to produce a work based on this file, this file does not
29 // by itself cause the resulting work to be covered by the GNU General Public
30 // License. However the source code for this file must still be made available
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34 // this file might be covered by the GNU General Public License.
36 // Alternative licenses for eCos may be arranged by contacting Red Hat, Inc.
37 // at http://sources.redhat.com/ecos/ecos-license/
38 // -------------------------------------------
39 //####ECOSGPLCOPYRIGHTEND####
40 //===========================================================================
41 //#####DESCRIPTIONBEGIN####
43 // Author(s): jlarmour
44 // Contributors: jlarmour
50 //####DESCRIPTIONEND####
52 //===========================================================================
56 #include <pkgconf/libm.h> // Configuration header
58 // Include the Math library?
61 // Derived from code with the following copyright
64 /* @(#)k_tan.c 1.3 95/01/18 */
66 * ====================================================
67 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
69 * Developed at SunSoft, a Sun Microsystems, Inc. business.
70 * Permission to use, copy, modify, and distribute this
71 * software is freely granted, provided that this notice
73 * ====================================================
76 /* __kernel_tan( x, y, k )
77 * kernel tan function on [-pi/4, pi/4], pi/4 ~ 0.7854
78 * Input x is assumed to be bounded by ~pi/4 in magnitude.
79 * Input y is the tail of x.
80 * Input k indicates whether tan (if k=1) or
81 * -1/tan (if k= -1) is returned.
84 * 1. Since tan(-x) = -tan(x), we need only to consider positive x.
85 * 2. if x < 2^-28 (hx<0x3e300000 0), return x with inexact if x!=0.
86 * 3. tan(x) is approximated by a odd polynomial of degree 27 on
89 * tan(x) ~ x + T1*x + ... + T13*x
92 * |tan(x) 2 4 26 | -59.2
93 * |----- - (1+T1*x +T2*x +.... +T13*x )| <= 2
96 * Note: tan(x+y) = tan(x) + tan'(x)*y
97 * ~ tan(x) + (1+x*x)*y
98 * Therefore, for better accuracy in computing tan(x+y), let
100 * r = x *(T2+x *(T3+x *(...+x *(T12+x *T13))))
103 * tan(x+y) = x + (T1*x + (x *(r+y)+y))
105 * 4. For x in [0.67434,pi/4], let y = pi/4 - x, then
106 * tan(x) = tan(pi/4-y) = (1-tan(y))/(1+tan(y))
107 * = 1 - 2*(tan(y) - (tan(y)^2)/(1+tan(y)))
110 #include "mathincl/fdlibm.h"
112 one = 1.00000000000000000000e+00, /* 0x3FF00000, 0x00000000 */
113 pio4 = 7.85398163397448278999e-01, /* 0x3FE921FB, 0x54442D18 */
114 pio4lo= 3.06161699786838301793e-17, /* 0x3C81A626, 0x33145C07 */
116 3.33333333333334091986e-01, /* 0x3FD55555, 0x55555563 */
117 1.33333333333201242699e-01, /* 0x3FC11111, 0x1110FE7A */
118 5.39682539762260521377e-02, /* 0x3FABA1BA, 0x1BB341FE */
119 2.18694882948595424599e-02, /* 0x3F9664F4, 0x8406D637 */
120 8.86323982359930005737e-03, /* 0x3F8226E3, 0xE96E8493 */
121 3.59207910759131235356e-03, /* 0x3F6D6D22, 0xC9560328 */
122 1.45620945432529025516e-03, /* 0x3F57DBC8, 0xFEE08315 */
123 5.88041240820264096874e-04, /* 0x3F4344D8, 0xF2F26501 */
124 2.46463134818469906812e-04, /* 0x3F3026F7, 0x1A8D1068 */
125 7.81794442939557092300e-05, /* 0x3F147E88, 0xA03792A6 */
126 7.14072491382608190305e-05, /* 0x3F12B80F, 0x32F0A7E9 */
127 -1.85586374855275456654e-05, /* 0xBEF375CB, 0xDB605373 */
128 2.59073051863633712884e-05, /* 0x3EFB2A70, 0x74BF7AD4 */
131 double __kernel_tan(double x, double y, int iy)
135 hx = CYG_LIBM_HI(x); /* high word of x */
136 ix = hx&0x7fffffff; /* high word of |x| */
137 if(ix<0x3e300000) /* x < 2**-28 */
138 {if((int)x==0) { /* generate inexact */
139 if(((ix|CYG_LIBM_LO(x))|(iy+1))==0) return one/fabs(x);
140 else return (iy==1)? x: -one/x;
143 if(ix>=0x3FE59428) { /* |x|>=0.6744 */
144 if(hx<0) {x = -x; y = -y;}
151 /* Break x^5*(T[1]+x^2*T[2]+...) into
152 * x^5(T[1]+x^4*T[3]+...+x^20*T[11]) +
153 * x^5(x^2*(T[2]+x^4*T[4]+...+x^22*[T12]))
155 r = T[1]+w*(T[3]+w*(T[5]+w*(T[7]+w*(T[9]+w*T[11]))));
156 v = z*(T[2]+w*(T[4]+w*(T[6]+w*(T[8]+w*(T[10]+w*T[12])))));
158 r = y + z*(s*(r+v)+y);
163 return (double)(1-((hx>>30)&2))*(v-2.0*(x-(w*w/(w+v)-r)));
166 else { /* if allow error up to 2 ulp,
167 simply return -1.0/(x+r) here */
168 /* compute -1.0/(x+r) accurately */
172 v = r-(z - x); /* z+v = r+x */
173 t = a = -1.0/w; /* a = -1.0/w */
180 #endif // ifdef CYGPKG_LIBM