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- /*
- * ====================================================
- * 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.
- * ====================================================
- */
- /* 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 "math.h"
- #include "math_private.h"
- 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) 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 */
- }
- }
- libm_hidden_def(tan)
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