atan2f.c raw

   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  }
  84