/* Modified version of k_cos.c for vbcc-PowerPC */

/*
 * ====================================================
 * 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 <math.h>
#include "vcmath.h"

static const double 
  one   =  1.00000000000000000000e+00, /* 0x3FF00000, 0x00000000 */
  pio4  =  7.85398163397448278999e-01, /* 0x3FE921FB, 0x54442D18 */
  pio4lo=  3.06161699786838301793e-17; /* 0x3C81A626, 0x33145C07 */
static const double T[] =  {
  3.33333333333334091986e-01, /* 0x3FD55555, 0x55555563 */
  1.33333333333201242699e-01, /* 0x3FC11111, 0x1110FE7A */
  5.39682539762260521377e-02, /* 0x3FABA1BA, 0x1BB341FE */
  2.18694882948595424599e-02, /* 0x3F9664F4, 0x8406D637 */
  8.86323982359930005737e-03, /* 0x3F8226E3, 0xE96E8493 */
  3.59207910759131235356e-03, /* 0x3F6D6D22, 0xC9560328 */
  1.45620945432529025516e-03, /* 0x3F57DBC8, 0xFEE08315 */
  5.88041240820264096874e-04, /* 0x3F4344D8, 0xF2F26501 */
  2.46463134818469906812e-04, /* 0x3F3026F7, 0x1A8D1068 */
  7.81794442939557092300e-05, /* 0x3F147E88, 0xA03792A6 */
  7.14072491382608190305e-05, /* 0x3F12B80F, 0x32F0A7E9 */
 -1.85586374855275456654e-05, /* 0xBEF375CB, 0xDB605373 */
  2.59073051863633712884e-05, /* 0x3EFB2A70, 0x74BF7AD4 */
};


double __kernel_tan(double x, double y, int iy)
{
  double z,r,v,w,s;
  long hx = __get_high_word(&x);
  long ix = hx&0x7fffffff;              /* high word of |x| */

  if(ix<0x3e300000) {                   /* x < 2**-28 */
    if((int)x==0) {                     /* generate inexact */
      if(((ix|__get_low_word(&x))|(iy+1))==0)
        return one/fabs(x);
      else
        return (iy==1)? x: -one/x;
    }
  }

  if(ix>=0x3FE59428) {                  /* |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>=0x3FE59428) {
    v = (double)iy;
    return (double)(1-((hx>>30)&2))*(v-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 */
    double a,t;
    z  = w;
    __set_low_word(&z,0);
    v  = r-(z - x);                     /* z+v = r+x */
    t = a  = -(1.0/w);                  /* a = -1.0/w */
    __set_low_word(&t,0);
    s  = 1.0+t*z;
    return t+a*(s+t*v);
  }
}