mirror of https://github.com/PrimeDecomp/prime.git
74 lines
1.9 KiB
C
74 lines
1.9 KiB
C
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/* @(#)s_tan.c 1.2 95/01/04 */
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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 SunPro, 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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/* 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 sin(x) cos(x) 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 tan(double x)
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#else
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double 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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_INT32 n, ix; /*- cc 020130 -*/
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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)
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return __kernel_tan(x, z, 1);
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/* tan(Inf or NaN) is NaN */
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else if (ix >= 0x7ff00000)
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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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