/* origin: FreeBSD /usr/src/lib/msun/src/e_atan2f.c */
/*
 * Conversion to float by Ian Lance Taylor, Cygnus Support, ian@cygnus.com.
 */
/*
 * ====================================================
 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
 *
 * Developed at SunPro, a Sun Microsystems, Inc. business.
 * Permission to use, copy, modify, and distribute this
 * software is freely granted, provided that this notice
 * is preserved.
 * ====================================================
 */

#include "libm.h"

static const float pi = 3.1415927410e+00, /* 0x40490fdb */
    pi_lo = -8.7422776573e-08;            /* 0xb3bbbd2e */

float atan2f(float y, float x) {
  float z;
  uint32_t m, ix, iy;

  if (isnan(x) || isnan(y))
    return x + y;
  GET_FLOAT_WORD(ix, x);
  GET_FLOAT_WORD(iy, y);
  if (ix == 0x3f800000) /* x=1.0 */
    return atanf(y);
  m = ((iy >> 31) & 1) | ((ix >> 30) & 2); /* 2*sign(x)+sign(y) */
  ix &= 0x7fffffff;
  iy &= 0x7fffffff;

  /* when y = 0 */
  if (iy == 0) {
    switch (m) {
      case 0:
      case 1:
        return y; /* atan(+-0,+anything)=+-0 */
      case 2:
        return pi; /* atan(+0,-anything) = pi */
      case 3:
        return -pi; /* atan(-0,-anything) =-pi */
    }
  }
  /* when x = 0 */
  if (ix == 0)
    return m & 1 ? -pi / 2 : pi / 2;
  /* when x is INF */
  if (ix == 0x7f800000) {
    if (iy == 0x7f800000) {
      switch (m) {
        case 0:
          return pi / 4; /* atan(+INF,+INF) */
        case 1:
          return -pi / 4; /* atan(-INF,+INF) */
        case 2:
          return 3 * pi / 4; /*atan(+INF,-INF)*/
        case 3:
          return -3 * pi / 4; /*atan(-INF,-INF)*/
      }
    } else {
      switch (m) {
        case 0:
          return 0.0f; /* atan(+...,+INF) */
        case 1:
          return -0.0f; /* atan(-...,+INF) */
        case 2:
          return pi; /* atan(+...,-INF) */
        case 3:
          return -pi; /* atan(-...,-INF) */
      }
    }
  }
  /* |y/x| > 0x1p26 */
  if (ix + (26 << 23) < iy || iy == 0x7f800000)
    return m & 1 ? -pi / 2 : pi / 2;

  /* z = atan(|y/x|) with correct underflow */
  if ((m & 2) && iy + (26 << 23) < ix) /*|y/x| < 0x1p-26, x < 0 */
    z = 0.0;
  else
    z = atanf(fabsf(y / x));
  switch (m) {
    case 0:
      return z; /* atan(+,+) */
    case 1:
      return -z; /* atan(-,+) */
    case 2:
      return pi - (z - pi_lo); /* atan(+,-) */
    default:                   /* case 3 */
      return (z - pi_lo) - pi; /* atan(-,-) */
  }
}