src/libm/s_tan.c
author Ryan C. Gordon <icculus@icculus.org>
Mon, 21 May 2018 12:00:21 -0400
changeset 11994 8e094f91ddab
parent 8842 f587255157cf
permissions -rw-r--r--
thread: fixed compiler warnings on non-Linux systems that use pthread.

(static function rtkit_setpriority was unused, moved it in with rest of
__LINUX__ section.)
     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 #include "math_libm.h"
    43 #include "math_private.h"
    44 
    45 double tan(double x)
    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 }
    67 libm_hidden_def(tan)