projects / uclibc-ng.git / blame
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|---|---|---|
| 7ce331c0 EA |
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 | |
| c4e44e97 | 7 | * software is freely granted, provided that this notice |
| 7ce331c0 EA |
8 | * is preserved. |
| 9 | * ==================================================== | |
| 10 | */ | |
| 11 | ||
| 7ce331c0 EA |
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. | |
| c4e44e97 EA |
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 | |
| 7ce331c0 EA |
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: | |
| c4e44e97 | 39 | * TRIG(x) returns trig(x) nearly rounded |
| 7ce331c0 EA |
40 | */ |
| 41 | ||
| 42 | #include "math.h" | |
| 43 | #include "math_private.h" | |
| 44 | ||
| 38b7304e | 45 | double tan(double x) |
| 7ce331c0 EA |
46 | { |
| 47 | double y[2],z=0.0; | |
| 48 | int32_t n, ix; | |
| 49 | ||
| 50 | /* High word of x. */ | |
| 51 | GET_HIGH_WORD(ix,x); | |
| 52 | ||
| 53 | /* |x| ~< pi/4 */ | |
| 54 | ix &= 0x7fffffff; | |
| 55 | if(ix <= 0x3fe921fb) return __kernel_tan(x,z,1); | |
| 56 | ||
| 57 | /* tan(Inf or NaN) is NaN */ | |
| 58 | else if (ix>=0x7ff00000) return x-x; /* NaN */ | |
| 59 | ||
| 60 | /* argument reduction needed */ | |
| 61 | else { | |
| 62 | n = __ieee754_rem_pio2(x,y); | |
| 63 | return __kernel_tan(y[0],y[1],1-((n&1)<<1)); /* 1 -- n even | |
| 64 | -1 -- n odd */ | |
| 65 | } | |
| 66 | } | |
| 9cc29786 | 67 | libm_hidden_def(tan) |