sysdeps/libm-ieee754/e_atan2f.c

   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 #if defined(LIBM_SCCS) && !defined(lint)
  17 static char rcsid[] = "$NetBSD: e_atan2f.c,v 1.4 1995/05/10 20:44:53 jtc Exp $";
  18 #endif
  19
  20 #include "math.h"
  21 #include "math_private.h"
  22
  23 #ifdef __STDC__
  24 static const float
  25 #else
  26 static float
  27 #endif
  28 tiny  = 1.0e-30,
  29 zero  = 0.0,
  30 pi_o_4  = 7.8539818525e-01,  /* 0x3f490fdb */
  31 pi_o_2  = 1.5707963705e+00,  /* 0x3fc90fdb */
  32 pi      = 3.1415927410e+00,  /* 0x40490fdb */
  33 pi_lo   = -8.7422776573e-07; /* 0xb3bbbd2e */
  34
  35 #ifdef __STDC__
  36         float __ieee754_atan2f(float y, float x)
  37 #else
  38         float __ieee754_atan2f(y,x)
  39         float  y,x;
  40 #endif
  41 {
  42         float z;
  43         int32_t k,m,hx,hy,ix,iy;
  44
  45         GET_FLOAT_WORD(hx,x);
  46         ix = hx&0x7fffffff;
  47         GET_FLOAT_WORD(hy,y);
  48         iy = hy&0x7fffffff;
  49         if((ix>0x7f800000)||
  50            (iy>0x7f800000))     /* x or y is NaN */
  51            return x+y;
  52         if(hx==0x3f800000) return __atanf(y);   /* x=1.0 */
  53         m = ((hy>>31)&1)|((hx>>30)&2);  /* 2*sign(x)+sign(y) */
  54
  55     /* when y = 0 */
  56         if(iy==0) {
  57             switch(m) {
  58                 case 0:
  59                 case 1: return y;       /* atan(+-0,+anything)=+-0 */
  60                 case 2: return  pi+tiny;/* atan(+0,-anything) = pi */
  61                 case 3: return -pi-tiny;/* atan(-0,-anything) =-pi */
  62             }
  63         }
  64     /* when x = 0 */
  65         if(ix==0) return (hy<0)?  -pi_o_2-tiny: pi_o_2+tiny;
  66
  67     /* when x is INF */
  68         if(ix==0x7f800000) {
  69             if(iy==0x7f800000) {
  70                 switch(m) {
  71                     case 0: return  pi_o_4+tiny;/* atan(+INF,+INF) */
  72                     case 1: return -pi_o_4-tiny;/* atan(-INF,+INF) */
  73                     case 2: return  (float)3.0*pi_o_4+tiny;/*atan(+INF,-INF)*/
  74                     case 3: return (float)-3.0*pi_o_4-tiny;/*atan(-INF,-INF)*/
  75                 }
  76             } else {
  77                 switch(m) {
  78                     case 0: return  zero  ;     /* atan(+...,+INF) */
  79                     case 1: return -zero  ;     /* atan(-...,+INF) */
  80                     case 2: return  pi+tiny  ;  /* atan(+...,-INF) */
  81                     case 3: return -pi-tiny  ;  /* atan(-...,-INF) */
  82                 }
  83             }
  84         }
  85     /* when y is INF */
  86         if(iy==0x7f800000) return (hy<0)? -pi_o_2-tiny: pi_o_2+tiny;
  87
  88     /* compute y/x */
  89         k = (iy-ix)>>23;
  90         if(k > 60) z=pi_o_2+(float)0.5*pi_lo;   /* |y/x| >  2**60 */
  91         else if(hx<0&&k<-60) z=0.0;     /* |y|/x < -2**60 */
  92         else z=__atanf(fabsf(y/x));     /* safe to do y/x */
  93         switch (m) {
  94             case 0: return       z  ;   /* atan(+,+) */
  95             case 1: {
  96                       u_int32_t zh;
  97                       GET_FLOAT_WORD(zh,z);
  98                       SET_FLOAT_WORD(z,zh ^ 0x80000000);
  99                     }
 100                     return       z  ;   /* atan(-,+) */
 101             case 2: return  pi-(z-pi_lo);/* atan(+,-) */
 102             default: /* case 3 */
 103                     return  (z-pi_lo)-pi;/* atan(-,-) */
 104         }
 105 }