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k_tanf.c revision 1.2 
      1 /* k_tanf.c -- float version of k_tan.c
      2  * Conversion to float by Ian Lance Taylor, Cygnus Support, ian (at) 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 #ifndef lint
     17 static char rcsid[] = "$Id: k_tanf.c,v 1.2 1994/08/18 23:06:18 jtc Exp $";
     18 #endif
     19 
     20 #include "math.h"
     21 #include "math_private.h"
     22 #ifdef __STDC__
     23 static const float
     24 #else
     25 static float
     26 #endif
     27 one   =  1.0000000000e+00, /* 0x3f800000 */
     28 pio4  =  7.8539812565e-01, /* 0x3f490fda */
     29 pio4lo=  3.7748947079e-08, /* 0x33222168 */
     30 T[] =  {
     31   3.3333334327e-01, /* 0x3eaaaaab */
     32   1.3333334029e-01, /* 0x3e088889 */
     33   5.3968254477e-02, /* 0x3d5d0dd1 */
     34   2.1869488060e-02, /* 0x3cb327a4 */
     35   8.8632395491e-03, /* 0x3c11371f */
     36   3.5920790397e-03, /* 0x3b6b6916 */
     37   1.4562094584e-03, /* 0x3abede48 */
     38   5.8804126456e-04, /* 0x3a1a26c8 */
     39   2.4646313977e-04, /* 0x398137b9 */
     40   7.8179444245e-05, /* 0x38a3f445 */
     41   7.1407252108e-05, /* 0x3895c07a */
     42  -1.8558637748e-05, /* 0xb79bae5f */
     43   2.5907305826e-05, /* 0x37d95384 */
     44 };
     45 
     46 #ifdef __STDC__
     47 	float __kernel_tanf(float x, float y, int iy)
     48 #else
     49 	float __kernel_tanf(x, y, iy)
     50 	float x,y; int iy;
     51 #endif
     52 {
     53 	float z,r,v,w,s;
     54 	int32_t ix,hx;
     55 	GET_FLOAT_WORD(hx,x);
     56 	ix = hx&0x7fffffff;	/* high word of |x| */
     57 	if(ix<0x31800000)			/* x < 2**-28 */
     58 	    {if((int)x==0) {			/* generate inexact */
     59 		if((ix|(iy+1))==0) return one/fabsf(x);
     60 		else return (iy==1)? x: -one/x;
     61 	    }
     62 	    }
     63 	if(ix>=0x3f2ca140) { 			/* |x|>=0.6744 */
     64 	    if(hx<0) {x = -x; y = -y;}
     65 	    z = pio4-x;
     66 	    w = pio4lo-y;
     67 	    x = z+w; y = 0.0;
     68 	}
     69 	z	=  x*x;
     70 	w 	=  z*z;
     71     /* Break x^5*(T[1]+x^2*T[2]+...) into
     72      *	  x^5(T[1]+x^4*T[3]+...+x^20*T[11]) +
     73      *	  x^5(x^2*(T[2]+x^4*T[4]+...+x^22*[T12]))
     74      */
     75 	r = T[1]+w*(T[3]+w*(T[5]+w*(T[7]+w*(T[9]+w*T[11]))));
     76 	v = z*(T[2]+w*(T[4]+w*(T[6]+w*(T[8]+w*(T[10]+w*T[12])))));
     77 	s = z*x;
     78 	r = y + z*(s*(r+v)+y);
     79 	r += T[0]*s;
     80 	w = x+r;
     81 	if(ix>=0x3f2ca140) {
     82 	    v = (float)iy;
     83 	    return (float)(1-((hx>>30)&2))*(v-(float)2.0*(x-(w*w/(w+v)-r)));
     84 	}
     85 	if(iy==1) return w;
     86 	else {		/* if allow error up to 2 ulp,
     87 			   simply return -1.0/(x+r) here */
     88      /*  compute -1.0/(x+r) accurately */
     89 	    float a,t;
     90 	    int32_t i;
     91 	    z  = w;
     92 	    GET_FLOAT_WORD(i,z);
     93 	    SET_FLOAT_WORD(z,i&0xfffff000);
     94 	    v  = r-(z - x); 	/* z+v = r+x */
     95 	    t = a  = -(float)1.0/w;	/* a = -1.0/w */
     96 	    GET_FLOAT_WORD(i,t);
     97 	    SET_FLOAT_WORD(t,i&0xfffff000);
     98 	    s  = (float)1.0+t*z;
     99 	    return t+a*(s+t*v);
    100 	}
    101 }
    102