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72 lines
1.8 KiB
72 lines
1.8 KiB
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/* @(#)s_tan.c 1.3 95/01/18 */ |
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/* |
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* ==================================================== |
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* Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved. |
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* |
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* Developed at SunSoft, a Sun Microsystems, Inc. business. |
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* Permission to use, copy, modify, and distribute this |
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* software is freely granted, provided that this notice |
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* is preserved. |
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* ==================================================== |
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*/ |
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/* ieee_tan(x) |
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* Return tangent function of x. |
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* |
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* kernel function: |
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* __kernel_tan ... tangent function on [-pi/4,pi/4] |
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* __ieee754_rem_pio2 ... argument reduction routine |
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* |
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* Method. |
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* Let S,C and T denote the sin, cos and tan respectively on |
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* [-PI/4, +PI/4]. Reduce the argument x to y1+y2 = x-k*pi/2 |
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* in [-pi/4 , +pi/4], and let n = k mod 4. |
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* We have |
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* |
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* n ieee_sin(x) ieee_cos(x) ieee_tan(x) |
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* ---------------------------------------------------------- |
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* 0 S C T |
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* 1 C -S -1/T |
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* 2 -S -C T |
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* 3 -C S -1/T |
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* ---------------------------------------------------------- |
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* |
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* Special cases: |
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* Let trig be any of sin, cos, or tan. |
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* trig(+-INF) is NaN, with signals; |
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* trig(NaN) is that NaN; |
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* |
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* Accuracy: |
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* TRIG(x) returns trig(x) nearly rounded |
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*/ |
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#include "fdlibm.h" |
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#ifdef __STDC__ |
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double ieee_tan(double x) |
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#else |
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double ieee_tan(x) |
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double x; |
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#endif |
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{ |
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double y[2],z=0.0; |
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int n, ix; |
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/* High word of x. */ |
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ix = __HI(x); |
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/* |x| ~< pi/4 */ |
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ix &= 0x7fffffff; |
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if(ix <= 0x3fe921fb) return __kernel_tan(x,z,1); |
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/* ieee_tan(Inf or NaN) is NaN */ |
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else if (ix>=0x7ff00000) return x-x; /* NaN */ |
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/* argument reduction needed */ |
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else { |
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n = __ieee754_rem_pio2(x,y); |
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return __kernel_tan(y[0],y[1],1-((n&1)<<1)); /* 1 -- n even |
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-1 -- n odd */ |
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} |
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}
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