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Diffstat (limited to 'src/math/tan.c')
-rw-r--r-- | src/math/tan.c | 69 |
1 files changed, 69 insertions, 0 deletions
diff --git a/src/math/tan.c b/src/math/tan.c new file mode 100644 index 00000000..2e1f3c83 --- /dev/null +++ b/src/math/tan.c @@ -0,0 +1,69 @@ +/* origin: FreeBSD /usr/src/lib/msun/src/s_tan.c */ +/* + * ==================================================== + * 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: + * __tan ... tangent function on [-pi/4,pi/4] + * __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 "libm.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) { + if (ix < 0x3e400000) /* x < 2**-27 */ + /* raise inexact if x != 0 */ + if ((int)x == 0) + return x; + return __tan(x, z, 1); + } + + /* tan(Inf or NaN) is NaN */ + if (ix >= 0x7ff00000) + return x - x; + + /* argument reduction needed */ + n = __rem_pio2(x, y); + return __tan(y[0], y[1], 1 - ((n&1)<<1)); /* n even: 1, n odd: -1 */ +} |