Quelle s_tan.cpp Sprache: C

/* @(#)s_tan.c 5.1 93/09/24 */
/*
* ====================================================
* Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
*
* Developed at SunPro, a Sun Microsystems, Inc. business.
* Permission to use, copy, modify, and distribute this
* software is freely granted, provided that this notice
* is preserved.
* ====================================================
*/

//#include <sys/cdefs.h>
//__FBSDID("$FreeBSD$");

/* tan(x)
* Return tangent function of x.
*
* kernel function:
* __kernel_tan ... tangent function on [-pi/4,pi/4]
* __ieee754_rem_pio2 ... argument reduction routine
*
* Method.
*      Let S,C and T denote the sin, cos and tan respectively on
* [-PI/4, +PI/4]. Reduce the argument x to y1+y2 = x-k*pi/2
* in [-pi/4 , +pi/4], and let n = k mod 4.
* We have
*
*          n        sin(x)      cos(x)        tan(x)
*     ----------------------------------------------------------
*     0        S    C T
*     1        C   -S -1/T
*     2       -S   -C T
*     3       -C    S -1/T
*     ----------------------------------------------------------
*
* Special cases:
*      Let trig be any of sin, cos, or tan.
*      trig(+-INF)  is NaN, with signals;
*      trig(NaN)    is that NaN;
*
* Accuracy:
* TRIG(x) returns trig(x) nearly rounded
*/

#include <float.h>

#define INLINE_REM_PIO2
#include "math_private.h"
#include "e_rem_pio2.cpp"

double
tan(double x)
{
double y[2],z=0.0;
int32_t n, ix;

    /* High word of x. */
GET_HIGH_WORD(ix,x);

    /* |x| ~< pi/4 */
ix &= 0x7fffffff;
if(ix <= 0x3fe921fb) {
     if(ix<0x3e400000)   /* x < 2**-27 */
  if((int)x==0) return x;  /* generate inexact */
     return __kernel_tan(x,z,1);
}

    /* tan(Inf or NaN) is NaN */
else if (ix>=0x7ff00000) return x-x;  /* NaN */

    /* argument reduction needed */
else {
     n = __ieee754_rem_pio2(x,y);
     return __kernel_tan(y[0],y[1],1-((n&1)<<1)); /*   1 -- n even
-1 -- n odd */
}
}

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