gonzui

    1: /* e_atan2f.c -- float version of e_atan2.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: tiny  = 1.0e-30,
   21: zero  = 0.0,
   22: pi_o_4  = 7.8539818525e-01, /* 0x3f490fdb */
   23: pi_o_2  = 1.5707963705e+00, /* 0x3fc90fdb */
   24: pi      = 3.1415925026e+00, /* 0x40490fda */
   25: pi_lo   = 1.5099578832e-07; /* 0x34222168 */
   26: 
   27: float
   28: atan2f(float y, float x)
   29: {  
   30:         float z;
   31:         int32_t k,m,hx,hy,ix,iy;
   32: 
   33:         GET_FLOAT_WORD(hx,x);
   34:         ix = hx&0x7fffffff;
   35:         GET_FLOAT_WORD(hy,y);
   36:         iy = hy&0x7fffffff;
   37:         if((ix>0x7f800000)||
   38:            (iy>0x7f800000))    /* x or y is NaN */
   39:            return x+y;
   40:         if(hx==0x3f800000) return atanf(y);   /* x=1.0 */
   41:         m = ((hy>>31)&1)|((hx>>30)&2); /* 2*sign(x)+sign(y) */
   42: 
   43:     /* when y = 0 */
   44:         if(iy==0) {
   45:             switch(m) {
   46:                 case 0: 
   47:                 case 1: return y;     /* atan(+-0,+anything)=+-0 */
   48:                 case 2: return  pi+tiny;/* atan(+0,-anything) = pi */
   49:                 case 3: return -pi-tiny;/* atan(-0,-anything) =-pi */
   50:             }
   51:         }
   52:     /* when x = 0 */
   53:         if(ix==0) return (hy<0)?  -pi_o_2-tiny: pi_o_2+tiny;
   54:             
   55:     /* when x is INF */
   56:         if(ix==0x7f800000) {
   57:             if(iy==0x7f800000) {
   58:                 switch(m) {
   59:                     case 0: return  pi_o_4+tiny;/* atan(+INF,+INF) */
   60:                     case 1: return -pi_o_4-tiny;/* atan(-INF,+INF) */
   61:                     case 2: return  (float)3.0*pi_o_4+tiny;/*atan(+INF,-INF)*/
   62:                     case 3: return (float)-3.0*pi_o_4-tiny;/*atan(-INF,-INF)*/
   63:                 }
   64:             } else {
   65:                 switch(m) {
   66:                     case 0: return  zero  ;   /* atan(+...,+INF) */
   67:                     case 1: return -zero  ;   /* atan(-...,+INF) */
   68:                     case 2: return  pi+tiny  ;        /* atan(+...,-INF) */
   69:                     case 3: return -pi-tiny  ;        /* atan(-...,-INF) */
   70:                 }
   71:             }
   72:         }
   73:     /* when y is INF */
   74:         if(iy==0x7f800000) return (hy<0)? -pi_o_2-tiny: pi_o_2+tiny;
   75: 
   76:     /* compute y/x */
   77:         k = (iy-ix)>>23;
   78:         if(k > 60) z=pi_o_2+(float)0.5*pi_lo;  /* |y/x| >  2**60 */
   79:         else if(hx<0&&k<-60) z=0.0;    /* |y|/x < -2**60 */
   80:         else z=atanf(fabsf(y/x));      /* safe to do y/x */
   81:         switch (m) {
   82:             case 0: return       z  ;  /* atan(+,+) */
   83:             case 1: {
   84:                      u_int32_t zh;
   85:                       GET_FLOAT_WORD(zh,z);
   86:                       SET_FLOAT_WORD(z,zh ^ 0x80000000);
   87:                     }
   88:                     return       z  ; /* atan(-,+) */
   89:             case 2: return  pi-(z-pi_lo);/* atan(+,-) */
   90:             default: /* case 3 */
   91:                    return  (z-pi_lo)-pi;/* atan(-,-) */
   92:         }
   93: }