source: vendor/FreeBSD-msun/5.x-2005-06-xx/src/k_tanf.c

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

/*
 * ====================================================
 * Copyright 2004 Sun Microsystems, Inc.  All Rights Reserved.
 *
 * 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/k_tanf.c,v 1.8 2004/06/02 04:39:44 das Exp $";
#endif

#include "math.h"
#include "math_private.h"
static const float
one   =  1.0000000000e+00, /* 0x3f800000 */
pio4  =  7.8539812565e-01, /* 0x3f490fda */
pio4lo=  3.7748947079e-08, /* 0x33222168 */
T[] =  {
  3.3333334327e-01, /* 0x3eaaaaab */
  1.3333334029e-01, /* 0x3e088889 */
  5.3968254477e-02, /* 0x3d5d0dd1 */
  2.1869488060e-02, /* 0x3cb327a4 */
  8.8632395491e-03, /* 0x3c11371f */
  3.5920790397e-03, /* 0x3b6b6916 */
  1.4562094584e-03, /* 0x3abede48 */
  5.8804126456e-04, /* 0x3a1a26c8 */
  2.4646313977e-04, /* 0x398137b9 */
  7.8179444245e-05, /* 0x38a3f445 */
  7.1407252108e-05, /* 0x3895c07a */
 -1.8558637748e-05, /* 0xb79bae5f */
  2.5907305826e-05, /* 0x37d95384 */
};

float
__kernel_tanf(float x, float y, int iy)
{
        float z,r,v,w,s;
        int32_t ix,hx;
        GET_FLOAT_WORD(hx,x);
        ix = hx&0x7fffffff;     /* high word of |x| */
        if(ix<0x31800000) {                     /* x < 2**-28 */
                if ((int) x == 0) {             /* generate inexact */
                        if ((ix | (iy + 1)) == 0)
                                return one / fabsf(x);
                        else {
                                if (iy == 1)
                                        return x;
                                else {  /* compute -1 / (x+y) carefully */
                                        double a, t;

                                        z = w = x + y;
                                        GET_FLOAT_WORD(ix, z);
                                        SET_FLOAT_WORD(z, ix & 0xfffff000);
                                        v = y - (z - x);
                                        t = a = -one / w;
                                        GET_FLOAT_WORD(ix, t);
                                        SET_FLOAT_WORD(t, ix & 0xfffff000);
                                        s = one + t * z;
                                        return t + a * (s + t * v);
                                }
                        }
                }
        }
        if(ix>=0x3f2ca140) {                    /* |x|>=0.6744 */
            if(hx<0) {x = -x; y = -y;}
            z = pio4-x;
            w = pio4lo-y;
            x = z+w; y = 0.0;
        }
        z       =  x*x;
        w       =  z*z;
    /* Break x^5*(T[1]+x^2*T[2]+...) into
     *    x^5(T[1]+x^4*T[3]+...+x^20*T[11]) +
     *    x^5(x^2*(T[2]+x^4*T[4]+...+x^22*[T12]))
     */
        r = T[1]+w*(T[3]+w*(T[5]+w*(T[7]+w*(T[9]+w*T[11]))));
        v = z*(T[2]+w*(T[4]+w*(T[6]+w*(T[8]+w*(T[10]+w*T[12])))));
        s = z*x;
        r = y + z*(s*(r+v)+y);
        r += T[0]*s;
        w = x+r;
        if(ix>=0x3f2ca140) {
            v = (float)iy;
            return (float)(1-((hx>>30)&2))*(v-(float)2.0*(x-(w*w/(w+v)-r)));
        }
        if(iy==1) return w;
        else {          /* if allow error up to 2 ulp,
                           simply return -1.0/(x+r) here */
     /*  compute -1.0/(x+r) accurately */
            float a,t;
            int32_t i;
            z  = w;
            GET_FLOAT_WORD(i,z);
            SET_FLOAT_WORD(z,i&0xfffff000);
            v  = r-(z - x);     /* z+v = r+x */
            t = a  = -(float)1.0/w;     /* a = -1.0/w */
            GET_FLOAT_WORD(i,t);
            SET_FLOAT_WORD(t,i&0xfffff000);
            s  = (float)1.0+t*z;
            return t+a*(s+t*v);
        }
}