gonzui

    1: /* k_tanf.c -- float version of k_tan.c
    2:  * Conversion to float by Ian Lance Taylor, Cygnus Support, ian@cygnus.com.
    3:  */
    4: 
    5: /*
    6:  * ====================================================
    7:  * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
    8:  *
    9:  * Developed at SunPro, a Sun Microsystems, Inc. business.
   10:  * Permission to use, copy, modify, and distribute this
   11:  * software is freely granted, provided that this notice 
   12:  * is preserved.
   13:  * ====================================================
   14:  */
   15: 
   16: #include "math.h"
   17: #include "math_private.h"
   18: 
   19: static const float 
   20: one   =  1.0000000000e+00, /* 0x3f800000 */
   21: pio4  =  7.8539812565e-01, /* 0x3f490fda */
   22: pio4lo=  3.7748947079e-08, /* 0x33222168 */
   23: T[] =  {
   24:   3.3333334327e-01, /* 0x3eaaaaab */
   25:   1.3333334029e-01, /* 0x3e088889 */
   26:   5.3968254477e-02, /* 0x3d5d0dd1 */
   27:   2.1869488060e-02, /* 0x3cb327a4 */
   28:   8.8632395491e-03, /* 0x3c11371f */
   29:   3.5920790397e-03, /* 0x3b6b6916 */
   30:   1.4562094584e-03, /* 0x3abede48 */
   31:   5.8804126456e-04, /* 0x3a1a26c8 */
   32:   2.4646313977e-04, /* 0x398137b9 */
   33:   7.8179444245e-05, /* 0x38a3f445 */
   34:   7.1407252108e-05, /* 0x3895c07a */
   35:  -1.8558637748e-05, /* 0xb79bae5f */
   36:   2.5907305826e-05, /* 0x37d95384 */
   37: };
   38: 
   39: float
   40: __kernel_tanf(float x, float y, int iy)
   41: {
   42:         float z,r,v,w,s;
   43:         int32_t ix,hx;
   44:         GET_FLOAT_WORD(hx,x);
   45:         ix = hx&0x7fffffff;    /* high word of |x| */
   46:         if(ix<0x31800000)                      /* x < 2**-28 */
   47:             {if((int)x==0) {                   /* generate inexact */
   48:                 if((ix|(iy+1))==0) return one/fabsf(x);
   49:                 else return (iy==1)? x: -one/x;
   50:             }
   51:             }
   52:         if(ix>=0x3f2ca140) {                   /* |x|>=0.6744 */
   53:             if(hx<0) {x = -x; y = -y;}
   54:             z = pio4-x;
   55:             w = pio4lo-y;
   56:             x = z+w; y = 0.0;
   57:         }
   58:         z      =  x*x;
   59:         w      =  z*z;
   60:     /* Break x^5*(T[1]+x^2*T[2]+...) into
   61:      *    x^5(T[1]+x^4*T[3]+...+x^20*T[11]) +
   62:      *    x^5(x^2*(T[2]+x^4*T[4]+...+x^22*[T12]))
   63:      */
   64:         r = T[1]+w*(T[3]+w*(T[5]+w*(T[7]+w*(T[9]+w*T[11]))));
   65:         v = z*(T[2]+w*(T[4]+w*(T[6]+w*(T[8]+w*(T[10]+w*T[12])))));
   66:         s = z*x;
   67:         r = y + z*(s*(r+v)+y);
   68:         r += T[0]*s;
   69:         w = x+r;
   70:         if(ix>=0x3f2ca140) {
   71:             v = (float)iy;
   72:             return (float)(1-((hx>>30)&2))*(v-(float)2.0*(x-(w*w/(w+v)-r)));
   73:         }
   74:         if(iy==1) return w;
   75:         else {         /* if allow error up to 2 ulp, 
   76:                            simply return -1.0/(x+r) here */
   77:      /*  compute -1.0/(x+r) accurately */
   78:             float a,t;
   79:             int32_t i;
   80:             z  = w;
   81:             GET_FLOAT_WORD(i,z);
   82:             SET_FLOAT_WORD(z,i&0xfffff000);
   83:             v  = r-(z - x);    /* z+v = r+x */
   84:             t = a  = -(float)1.0/w;    /* a = -1.0/w */
   85:             GET_FLOAT_WORD(i,t);
   86:             SET_FLOAT_WORD(t,i&0xfffff000);
   87:             s  = (float)1.0+t*z;
   88:             return t+a*(s+t*v);
   89:         }
   90: }