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
  16 #include <sys/cdefs.h>
  17 #if defined(LIBM_SCCS) && !defined(lint)
  18 __RCSID("$NetBSD: e_atan2f.c,v 1.7 2002/05/26 22:01:49 wiz Exp $");
  19 #endif
  20
  21 #include "math.h"
  22 #include "math_private.h"
  23
  24 static const float
  25 tiny  = 1.0e-30,
  26 zero  = 0.0,
  27 pi_o_4  = 7.8539818525e-01, /* 0x3f490fdb */
  28 pi_o_2  = 1.5707963705e+00, /* 0x3fc90fdb */
  29 pi      = 3.1415925026e+00, /* 0x40490fda */
  30 pi_lo   = 1.5099578832e-07; /* 0x34222168 */
  31
  32 float
  33 __ieee754_atan2f(float y, float x)
  34 {
  35         float z;
  36         int32_t k,m,hx,hy,ix,iy;
  37
  38         GET_FLOAT_WORD(hx,x);
  39         ix = hx&0x7fffffff;
  40         GET_FLOAT_WORD(hy,y);
  41         iy = hy&0x7fffffff;
  42         if((ix>0x7f800000)||
  43            (iy>0x7f800000))     /* x or y is NaN */
  44            return x+y;
  45         if(hx==0x3f800000) return atanf(y);   /* x=1.0 */
  46         m = ((hy>>31)&1)|((hx>>30)&2);  /* 2*sign(x)+sign(y) */
  47
  48     /* when y = 0 */
  49         if(iy==0) {
  50             switch(m) {
  51                 case 0:
  52                 case 1: return y;       /* atan(+-0,+anything)=+-0 */
  53                 case 2: return  pi+tiny;/* atan(+0,-anything) = pi */
  54                 case 3: return -pi-tiny;/* atan(-0,-anything) =-pi */
  55             }
  56         }
  57     /* when x = 0 */
  58         if(ix==0) return (hy<0)?  -pi_o_2-tiny: pi_o_2+tiny;
  59
  60     /* when x is INF */
  61         if(ix==0x7f800000) {
  62             if(iy==0x7f800000) {
  63                 switch(m) {
  64                     case 0: return  pi_o_4+tiny;/* atan(+INF,+INF) */
  65                     case 1: return -pi_o_4-tiny;/* atan(-INF,+INF) */
  66                     case 2: return  (float)3.0*pi_o_4+tiny;/*atan(+INF,-INF)*/
  67                     case 3: return (float)-3.0*pi_o_4-tiny;/*atan(-INF,-INF)*/
  68                 }
  69             } else {
  70                 switch(m) {
  71                     case 0: return  zero  ;     /* atan(+...,+INF) */
  72                     case 1: return -zero  ;     /* atan(-...,+INF) */
  73                     case 2: return  pi+tiny  ;  /* atan(+...,-INF) */
  74                     case 3: return -pi-tiny  ;  /* atan(-...,-INF) */
  75                 }
  76             }
  77         }
  78     /* when y is INF */
  79         if(iy==0x7f800000) return (hy<0)? -pi_o_2-tiny: pi_o_2+tiny;
  80
  81     /* compute y/x */
  82         k = (iy-ix)>>23;
  83         if(k > 60) z=pi_o_2+(float)0.5*pi_lo;   /* |y/x| >  2**60 */
  84         else if(hx<0&&k<-60) z=0.0;     /* |y|/x < -2**60 */
  85         else z=atanf(fabsf(y/x));       /* safe to do y/x */
  86         switch (m) {
  87             case 0: return       z  ;   /* atan(+,+) */
  88             case 1: {
  89                       u_int32_t zh;
  90                       GET_FLOAT_WORD(zh,z);
  91                       SET_FLOAT_WORD(z,zh ^ 0x80000000);
  92                     }
  93                     return       z  ;   /* atan(-,+) */
  94             case 2: return  pi-(z-pi_lo);/* atan(+,-) */
  95             default: /* case 3 */
  96                     return  (z-pi_lo)-pi;/* atan(-,-) */
  97         }
  98 }