1 /* From: @(#)k_tan.c 1.5 04/04/22 SMI */
2
3 /*
4 * ====================================================
5 * Copyright 2004 Sun Microsystems, Inc. All Rights Reserved.
6 * Copyright (c) 2008 Steven G. Kargl, David Schultz, Bruce D. Evans.
7 *
8 * Permission to use, copy, modify, and distribute this
9 * software is freely granted, provided that this notice
10 * is preserved.
11 * ====================================================
12 */
13
14
15 /*
16 * ld128 version of k_tan.c. See ../src/k_tan.c for most comments.
17 */
18
19
20
21 /*
22 * Domain [-0.67434, 0.67434], range ~[-3.37e-36, 1.982e-37]
23 * |tan(x)/x - t(x)| < 2**-117.8 (XXX should be ~1e-37)
24 *
25 * See ../ld80/k_cosl.c for more details about the polynomial.
26 */
27 static const long double
28 T3 = 0x1.5555555555555555555555555553p-2L,
29 T5 = 0x1.1111111111111111111111111eb5p-3L,
30 T7 = 0x1.ba1ba1ba1ba1ba1ba1ba1b694cd6p-5L,
31 T9 = 0x1.664f4882c10f9f32d6bbe09d8bcdp-6L,
32 T11 = 0x1.226e355e6c23c8f5b4f5762322eep-7L,
33 T13 = 0x1.d6d3d0e157ddfb5fed8e84e27b37p-9L,
34 T15 = 0x1.7da36452b75e2b5fce9ee7c2c92ep-10L,
35 T17 = 0x1.355824803674477dfcf726649efep-11L,
36 T19 = 0x1.f57d7734d1656e0aceb716f614c2p-13L,
37 T21 = 0x1.967e18afcb180ed942dfdc518d6cp-14L,
38 T23 = 0x1.497d8eea21e95bc7e2aa79b9f2cdp-15L,
39 T25 = 0x1.0b132d39f055c81be49eff7afd50p-16L,
40 T27 = 0x1.b0f72d33eff7bfa2fbc1059d90b6p-18L,
41 T29 = 0x1.5ef2daf21d1113df38d0fbc00267p-19L,
42 T31 = 0x1.1c77d6eac0234988cdaa04c96626p-20L,
43 T33 = 0x1.cd2a5a292b180e0bdd701057dfe3p-22L,
44 T35 = 0x1.75c7357d0298c01a31d0a6f7d518p-23L,
45 T37 = 0x1.2f3190f4718a9a520f98f50081fcp-24L,
46 pio4 = 0x1.921fb54442d18469898cc51701b8p-1L,
47 pio4lo = 0x1.cd129024e088a67cc74020bbea60p-116L;
48
49 static const double
50 T39 = 0.000000028443389121318352, /* 0x1e8a7592977938.0p-78 */
51 T41 = 0.000000011981013102001973, /* 0x19baa1b1223219.0p-79 */
52 T43 = 0.0000000038303578044958070, /* 0x107385dfb24529.0p-80 */
53 T45 = 0.0000000034664378216909893, /* 0x1dc6c702a05262.0p-81 */
54 T47 = -0.0000000015090641701997785, /* -0x19ecef3569ebb6.0p-82 */
55 T49 = 0.0000000029449552300483952, /* 0x194c0668da786a.0p-81 */
56 T51 = -0.0000000022006995706097711, /* -0x12e763b8845268.0p-81 */
57 T53 = 0.0000000015468200913196612, /* 0x1a92fc98c29554.0p-82 */
58 T55 = -0.00000000061311613386849674, /* -0x151106cbc779a9.0p-83 */
59 T57 = 1.4912469681508012e-10; /* 0x147edbdba6f43a.0p-85 */
60
61 long double
__kernel_tanl(long double x,long double y,int iy)62 __kernel_tanl(long double x, long double y, int iy) {
63 long double z, r, v, w, s;
64 long double osign;
65 int i;
66
67 iy = (iy == 1 ? -1 : 1); /* XXX recover original interface */
68 osign = (x >= 0 ? 1.0L : -1.0L); /* XXX slow, probably wrong for -0 */
69 if (fabsl(x) >= 0.67434L) {
70 if (x < 0) {
71 x = -x;
72 y = -y;
73 }
74 z = pio4 - x;
75 w = pio4lo - y;
76 x = z + w;
77 y = 0.0L;
78 i = 1;
79 } else
80 i = 0;
81 z = x * x;
82 w = z * z;
83 r = T5 + w * (T9 + w * (T13 + w * (T17 + w * (T21 +
84 w * (T25 + w * (T29 + w * (T33 +
85 w * (T37 + w * ((long double)T41 + w * ((long double)T45 + w * ((long double)T49 + w * ((long double)T53 +
86 w * (long double)T57))))))))))));
87 v = z * (T7 + w * (T11 + w * (T15 + w * (T19 + w * (T23 +
88 w * (T27 + w * (T31 + w * (T35 +
89 w * ((long double)T39 + w * ((long double)T43 + w * ((long double)T47 + w * ((long double)T51 + w * (long double)T55))))))))))));
90 s = z * x;
91 r = y + z * (s * (r + v) + y);
92 r += T3 * s;
93 w = x + r;
94 if (i == 1) {
95 v = (long double) iy;
96 return osign *
97 (v - 2.0L * (x - (w * w / (w + v) - r)));
98 }
99 if (iy == 1)
100 return w;
101 else {
102 /*
103 * if allow error up to 2 ulp, simply return
104 * -1.0 / (x+r) here
105 */
106 /* compute -1.0 / (x+r) accurately */
107 long double a, t;
108 z = w;
109 z = z + 0x1p32L - 0x1p32L;
110 v = r - (z - x); /* z+v = r+x */
111 t = a = -1.0L / w; /* a = -1.0/w */
112 t = t + 0x1p32L - 0x1p32L;
113 s = 1.0L + t * z;
114 return t + a * (s + t * v);
115 }
116 }
117
