source: asp3_tinet_ecnl_rx/trunk/musl-1.1.18/src/math/tanf.c@ 337

/* origin: FreeBSD /usr/src/lib/msun/src/s_tanf.c */
/*
 * Conversion to float by Ian Lance Taylor, Cygnus Support, ian@cygnus.com.
 * Optimized by Bruce D. Evans.
 */
/*
 * ====================================================
 * 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 "libm.h"

/* Small multiples of pi/2 rounded to double precision. */
static const double
t1pio2 = 1*M_PI_2, /* 0x3FF921FB, 0x54442D18 */
t2pio2 = 2*M_PI_2, /* 0x400921FB, 0x54442D18 */
t3pio2 = 3*M_PI_2, /* 0x4012D97C, 0x7F3321D2 */
t4pio2 = 4*M_PI_2; /* 0x401921FB, 0x54442D18 */

float tanf(float x)
{
        double y;
        uint32_t ix;
        unsigned n, sign;

        GET_FLOAT_WORD(ix, x);
        sign = ix >> 31;
        ix &= 0x7fffffff;

        if (ix <= 0x3f490fda) {  /* |x| ~<= pi/4 */
                if (ix < 0x39800000) {  /* |x| < 2**-12 */
                        /* raise inexact if x!=0 and underflow if subnormal */
                        FORCE_EVAL(ix < 0x00800000 ? x/0x1p120f : x+0x1p120f);
                        return x;
                }
                return __tandf(x, 0);
        }
        if (ix <= 0x407b53d1) {  /* |x| ~<= 5*pi/4 */
                if (ix <= 0x4016cbe3)  /* |x| ~<= 3pi/4 */
                        return __tandf((sign ? x+t1pio2 : x-t1pio2), 1);
                else
                        return __tandf((sign ? x+t2pio2 : x-t2pio2), 0);
        }
        if (ix <= 0x40e231d5) {  /* |x| ~<= 9*pi/4 */
                if (ix <= 0x40afeddf)  /* |x| ~<= 7*pi/4 */
                        return __tandf((sign ? x+t3pio2 : x-t3pio2), 1);
                else
                        return __tandf((sign ? x+t4pio2 : x-t4pio2), 0);
        }

        /* tan(Inf or NaN) is NaN */
        if (ix >= 0x7f800000)
                return x - x;

        /* argument reduction */
        n = __rem_pio2f(x, &y);
        return __tandf(y, n&1);
}