1 | /* s_tanl.c -- long double version of s_tan.c. |
2 | * Conversion to long double by Ulrich Drepper, |
3 | * Cygnus Support, drepper@cygnus.com. |
4 | */ |
5 | |
6 | /* |
7 | * ==================================================== |
8 | * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved. |
9 | * |
10 | * Developed at SunPro, a Sun Microsystems, Inc. business. |
11 | * Permission to use, copy, modify, and distribute this |
12 | * software is freely granted, provided that this notice |
13 | * is preserved. |
14 | * ==================================================== |
15 | */ |
16 | |
17 | #if defined(LIBM_SCCS) && !defined(lint) |
18 | static char rcsid[] = "$NetBSD: $" ; |
19 | #endif |
20 | |
21 | /* tanl(x) |
22 | * Return tangent function of x. |
23 | * |
24 | * kernel function: |
25 | * __kernel_tanl ... tangent function on [-pi/4,pi/4] |
26 | * __ieee754_rem_pio2l ... argument reduction routine |
27 | * |
28 | * Method. |
29 | * Let S,C and T denote the sin, cos and tan respectively on |
30 | * [-PI/4, +PI/4]. Reduce the argument x to y1+y2 = x-k*pi/2 |
31 | * in [-pi/4 , +pi/4], and let n = k mod 4. |
32 | * We have |
33 | * |
34 | * n sin(x) cos(x) tan(x) |
35 | * ---------------------------------------------------------- |
36 | * 0 S C T |
37 | * 1 C -S -1/T |
38 | * 2 -S -C T |
39 | * 3 -C S -1/T |
40 | * ---------------------------------------------------------- |
41 | * |
42 | * Special cases: |
43 | * Let trig be any of sin, cos, or tan. |
44 | * trig(+-INF) is NaN, with signals; |
45 | * trig(NaN) is that NaN; |
46 | * |
47 | * Accuracy: |
48 | * TRIG(x) returns trig(x) nearly rounded |
49 | */ |
50 | |
51 | #include <errno.h> |
52 | #include <math.h> |
53 | #include <math_private.h> |
54 | #include <libm-alias-ldouble.h> |
55 | |
56 | long double __tanl(long double x) |
57 | { |
58 | long double y[2],z=0.0; |
59 | int32_t n, se, i0, i1; |
60 | |
61 | /* High word of x. */ |
62 | GET_LDOUBLE_WORDS(se,i0,i1,x); |
63 | |
64 | /* |x| ~< pi/4 */ |
65 | se &= 0x7fff; |
66 | if(se <= 0x3ffe) return __kernel_tanl(x,z,1); |
67 | |
68 | /* tan(Inf or NaN) is NaN */ |
69 | else if (se==0x7fff) { |
70 | if (i1 == 0 && i0 == 0x80000000) |
71 | __set_errno (EDOM); |
72 | return x-x; |
73 | } |
74 | |
75 | /* argument reduction needed */ |
76 | else { |
77 | n = __ieee754_rem_pio2l(x,y); |
78 | return __kernel_tanl(y[0],y[1],1-((n&1)<<1)); /* 1 -- n even |
79 | -1 -- n odd */ |
80 | } |
81 | } |
82 | libm_alias_ldouble (__tan, tan) |
83 | |