source: vendor/FreeBSD-msun/current/src/s_tanf.c

/* s_tanf.c -- float version of s_tan.c.
 * Conversion to float by Ian Lance Taylor, Cygnus Support, ian@cygnus.com.
 */

/*
 * ====================================================
 * 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.
 * ====================================================
 */

#ifndef lint
static char rcsid[] = "$FreeBSD: src/lib/msun/src/s_tanf.c,v 1.7 2002/05/28 18:15:04 alfred Exp $";
#endif

#include "math.h"
#include "math_private.h"

float
tanf(float x)
{
        float y[2],z=0.0;
        int32_t n, ix;

        GET_FLOAT_WORD(ix,x);

    /* |x| ~< pi/4 */
        ix &= 0x7fffffff;
        if(ix <= 0x3f490fda) return __kernel_tanf(x,z,1);

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

    /* argument reduction needed */
        else {
            n = __ieee754_rem_pio2f(x,y);
            return __kernel_tanf(y[0],y[1],1-((n&1)<<1)); /*   1 -- n even
                                                              -1 -- n odd */
        }
}