/src/moddable/xs/tools/fdlibm/s_tan.c
Line | Count | Source |
1 | | /* |
2 | | * ==================================================== |
3 | | * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved. |
4 | | * |
5 | | * Developed at SunPro, a Sun Microsystems, Inc. business. |
6 | | * Permission to use, copy, modify, and distribute this |
7 | | * software is freely granted, provided that this notice |
8 | | * is preserved. |
9 | | * ==================================================== |
10 | | */ |
11 | | |
12 | | /* tan(x) |
13 | | * Return tangent function of x. |
14 | | * |
15 | | * kernel function: |
16 | | * __kernel_tan ... tangent function on [-pi/4,pi/4] |
17 | | * __ieee754_rem_pio2 ... argument reduction routine |
18 | | * |
19 | | * Method. |
20 | | * Let S,C and T denote the sin, cos and tan respectively on |
21 | | * [-PI/4, +PI/4]. Reduce the argument x to y1+y2 = x-k*pi/2 |
22 | | * in [-pi/4 , +pi/4], and let n = k mod 4. |
23 | | * We have |
24 | | * |
25 | | * n sin(x) cos(x) tan(x) |
26 | | * ---------------------------------------------------------- |
27 | | * 0 S C T |
28 | | * 1 C -S -1/T |
29 | | * 2 -S -C T |
30 | | * 3 -C S -1/T |
31 | | * ---------------------------------------------------------- |
32 | | * |
33 | | * Special cases: |
34 | | * Let trig be any of sin, cos, or tan. |
35 | | * trig(+-INF) is NaN, with signals; |
36 | | * trig(NaN) is that NaN; |
37 | | * |
38 | | * Accuracy: |
39 | | * TRIG(x) returns trig(x) nearly rounded |
40 | | */ |
41 | | |
42 | | #define INLINE_REM_PIO2 |
43 | | #include "math_private.h" |
44 | | #include "e_rem_pio2.c" |
45 | | |
46 | | double |
47 | | s_tan(double x) |
48 | 5.04k | { |
49 | 5.04k | double y[2],z=0.0; |
50 | 5.04k | int32_t n, ix; |
51 | | |
52 | | /* High word of x. */ |
53 | 5.04k | GET_HIGH_WORD(ix,x); |
54 | | |
55 | | /* |x| ~< pi/4 */ |
56 | 5.04k | ix &= 0x7fffffff; |
57 | 5.04k | if(ix <= 0x3fe921fb) { |
58 | 1.08k | if(ix<0x3e400000) /* x < 2**-27 */ |
59 | 280 | if((int)x==0) return x; /* generate inexact */ |
60 | 802 | return __kernel_tan(x,z,1); |
61 | 1.08k | } |
62 | | |
63 | | /* tan(Inf or NaN) is NaN */ |
64 | 3.96k | else if (ix>=0x7ff00000) return x-x; /* NaN */ |
65 | | |
66 | | /* argument reduction needed */ |
67 | 3.50k | else { |
68 | 3.50k | n = __ieee754_rem_pio2(x,y); |
69 | 3.50k | return __kernel_tan(y[0],y[1],1-((n&1)<<1)); /* 1 -- n even |
70 | | -1 -- n odd */ |
71 | 3.50k | } |
72 | 5.04k | } |