src/math/atan2f.c

   1 /* origin: FreeBSD /usr/src/lib/msun/src/e_atan2f.c */
   2 /*
   3  * Conversion to float by Ian Lance Taylor, Cygnus Support, ian@cygnus.com.
   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 "libm.h"
  17
  18 static const float
  19 pi     = 3.1415927410e+00, /* 0x40490fdb */
  20 pi_lo  = -8.7422776573e-08; /* 0xb3bbbd2e */
  21
  22 float atan2f(float y, float x)
  23 {
  24         float z;
  25         uint32_t m,ix,iy;
  26
  27         if (isnan(x) || isnan(y))
  28                 return x+y;
  29         GET_FLOAT_WORD(ix, x);
  30         GET_FLOAT_WORD(iy, y);
  31         if (ix == 0x3f800000)  /* x=1.0 */
  32                 return atanf(y);
  33         m = ((iy>>31)&1) | ((ix>>30)&2);  /* 2*sign(x)+sign(y) */
  34         ix &= 0x7fffffff;
  35         iy &= 0x7fffffff;
  36
  37         /* when y = 0 */
  38         if (iy == 0) {
  39                 switch (m) {
  40                 case 0:
  41                 case 1: return y;   /* atan(+-0,+anything)=+-0 */
  42                 case 2: return  pi; /* atan(+0,-anything) = pi */
  43                 case 3: return -pi; /* atan(-0,-anything) =-pi */
  44                 }
  45         }
  46         /* when x = 0 */
  47         if (ix == 0)
  48                 return m&1 ? -pi/2 : pi/2;
  49         /* when x is INF */
  50         if (ix == 0x7f800000) {
  51                 if (iy == 0x7f800000) {
  52                         switch (m) {
  53                         case 0: return  pi/4; /* atan(+INF,+INF) */
  54                         case 1: return -pi/4; /* atan(-INF,+INF) */
  55                         case 2: return 3*pi/4;  /*atan(+INF,-INF)*/
  56                         case 3: return -3*pi/4; /*atan(-INF,-INF)*/
  57                         }
  58                 } else {
  59                         switch (m) {
  60                         case 0: return  0.0f;    /* atan(+...,+INF) */
  61                         case 1: return -0.0f;    /* atan(-...,+INF) */
  62                         case 2: return  pi; /* atan(+...,-INF) */
  63                         case 3: return -pi; /* atan(-...,-INF) */
  64                         }
  65                 }
  66         }
  67         /* |y/x| > 0x1p26 */
  68         if (ix+(26<<23) < iy || iy == 0x7f800000)
  69                 return m&1 ? -pi/2 : pi/2;
  70
  71         /* z = atan(|y/x|) with correct underflow */
  72         if ((m&2) && iy+(26<<23) < ix)  /*|y/x| < 0x1p-26, x < 0 */
  73                 z = 0.0;
  74         else
  75                 z = atanf(fabsf(y/x));
  76         switch (m) {
  77         case 0: return z;              /* atan(+,+) */
  78         case 1: return -z;             /* atan(-,+) */
  79         case 2: return pi - (z-pi_lo); /* atan(+,-) */
  80         default: /* case 3 */
  81                 return (z-pi_lo) - pi; /* atan(-,-) */
  82         }
  83 }