lib/libm/src/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  * $NetBSD: e_atan2f.c,v 1.7 2002/05/26 22:01:49 wiz Exp $
  16  * $DragonFly: src/lib/libm/src/e_atan2f.c,v 1.1 2005/07/26 21:15:20 joerg Exp $
  17  */
  18
  19 #include <math.h>
  20 #include "math_private.h"
  21
  22 static const float
  23 tiny  = 1.0e-30,
  24 zero  = 0.0,
  25 pi_o_4  = 7.8539818525e-01, /* 0x3f490fdb */
  26 pi_o_2  = 1.5707963705e+00, /* 0x3fc90fdb */
  27 pi      = 3.1415925026e+00, /* 0x40490fda */
  28 pi_lo   = 1.5099578832e-07; /* 0x34222168 */
  29
  30 float
  31 atan2f(float y, float x)
  32 {
  33         float z;
  34         int32_t k,m,hx,hy,ix,iy;
  35
  36         GET_FLOAT_WORD(hx,x);
  37         ix = hx&0x7fffffff;
  38         GET_FLOAT_WORD(hy,y);
  39         iy = hy&0x7fffffff;
  40         if((ix>0x7f800000)||
  41            (iy>0x7f800000))     /* x or y is NaN */
  42            return x+y;
  43         if(hx==0x3f800000) return atanf(y);   /* x=1.0 */
  44         m = ((hy>>31)&1)|((hx>>30)&2);  /* 2*sign(x)+sign(y) */
  45
  46     /* when y = 0 */
  47         if(iy==0) {
  48             switch(m) {
  49                 case 0:
  50                 case 1: return y;       /* atan(+-0,+anything)=+-0 */
  51                 case 2: return  pi+tiny;/* atan(+0,-anything) = pi */
  52                 case 3: return -pi-tiny;/* atan(-0,-anything) =-pi */
  53             }
  54         }
  55     /* when x = 0 */
  56         if(ix==0) return (hy<0)?  -pi_o_2-tiny: pi_o_2+tiny;
  57
  58     /* when x is INF */
  59         if(ix==0x7f800000) {
  60             if(iy==0x7f800000) {
  61                 switch(m) {
  62                     case 0: return  pi_o_4+tiny;/* atan(+INF,+INF) */
  63                     case 1: return -pi_o_4-tiny;/* atan(-INF,+INF) */
  64                     case 2: return  (float)3.0*pi_o_4+tiny;/*atan(+INF,-INF)*/
  65                     case 3: return (float)-3.0*pi_o_4-tiny;/*atan(-INF,-INF)*/
  66                 }
  67             } else {
  68                 switch(m) {
  69                     case 0: return  zero  ;     /* atan(+...,+INF) */
  70                     case 1: return -zero  ;     /* atan(-...,+INF) */
  71                     case 2: return  pi+tiny  ;  /* atan(+...,-INF) */
  72                     case 3: return -pi-tiny  ;  /* atan(-...,-INF) */
  73                 }
  74             }
  75         }
  76     /* when y is INF */
  77         if(iy==0x7f800000) return (hy<0)? -pi_o_2-tiny: pi_o_2+tiny;
  78
  79     /* compute y/x */
  80         k = (iy-ix)>>23;
  81         if(k > 60) z=pi_o_2+(float)0.5*pi_lo;   /* |y/x| >  2**60 */
  82         else if(hx<0&&k<-60) z=0.0;     /* |y|/x < -2**60 */
  83         else z=atanf(fabsf(y/x));       /* safe to do y/x */
  84         switch (m) {
  85             case 0: return       z  ;   /* atan(+,+) */
  86             case 1: {
  87                       u_int32_t zh;
  88                       GET_FLOAT_WORD(zh,z);
  89                       SET_FLOAT_WORD(z,zh ^ 0x80000000);
  90                     }
  91                     return       z  ;   /* atan(-,+) */
  92             case 2: return  pi-(z-pi_lo);/* atan(+,-) */
  93             default: /* case 3 */
  94                     return  (z-pi_lo)-pi;/* atan(-,-) */
  95         }
  96 }