text: /* origin: FreeBSD /usr/src/lib/msun/src/e_atan2l.c */
  /*
   * ====================================================
   * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
   *
   * Developed at SunSoft, a Sun Microsystems, Inc. business.
   * Permission to use, copy, modify, and distribute this
   * software is freely granted, provided that this notice
   * is preserved.
   * ====================================================
   *
   */
  /*
   * See comments in atan2.c.
   * Converted to long double by David Schultz <das@FreeBSD.ORG>.
   */
  
  #include "libm.h"
  
  #if LDBL_MANT_DIG == 53 && LDBL_MAX_EXP == 1024
  long double atan2l(long double y, long double x)
  {
  	return atan2(y, x);
  }
  #elif (LDBL_MANT_DIG == 64 || LDBL_MANT_DIG == 113) && LDBL_MAX_EXP == 16384
  #include "__invtrigl.h"
  
  long double atan2l(long double y, long double x)
  {
  	union ldshape ux, uy;
  	long double z;
  	int m, ex, ey;
  
  	if (isnan(x) || isnan(y))
  		return x+y;
  	if (x == 1)
  		return atanl(y);
  	ux.f = x;
  	uy.f = y;
  	ex = ux.i.se & 0x7fff;
  	ey = uy.i.se & 0x7fff;
  	m = 2*(ux.i.se>>15) | uy.i.se>>15;
  	if (y == 0) {
  		switch(m) {
  		case 0:
  		case 1: return y;           /* atan(+-0,+anything)=+-0 */
  		case 2: return  2*pio2_hi;  /* atan(+0,-anything) = pi */
  		case 3: return -2*pio2_hi;  /* atan(-0,-anything) =-pi */
  		}
  	}
  	if (x == 0)
  		return m&1 ? -pio2_hi : pio2_hi;
  	if (ex == 0x7fff) {
  		if (ey == 0x7fff) {
  			switch(m) {
  			case 0: return  pio2_hi/2;   /* atan(+INF,+INF) */
  			case 1: return -pio2_hi/2;   /* atan(-INF,+INF) */
  			case 2: return  1.5*pio2_hi; /* atan(+INF,-INF) */
  			case 3: return -1.5*pio2_hi; /* atan(-INF,-INF) */
  			}
  		} else {
  			switch(m) {
  			case 0: return  0.0;        /* atan(+...,+INF) */
  			case 1: return -0.0;        /* atan(-...,+INF) */
  			case 2: return  2*pio2_hi;  /* atan(+...,-INF) */
  			case 3: return -2*pio2_hi;  /* atan(-...,-INF) */
  			}
  		}
  	}
  	if (ex+120 < ey || ey == 0x7fff)
  		return m&1 ? -pio2_hi : pio2_hi;
  	/* z = atan(|y/x|) without spurious underflow */
  	if ((m&2) && ey+120 < ex)  /* |y/x| < 0x1p-120, x<0 */
  		z = 0.0;
  	else
  		z = atanl(fabsl(y/x));
  	switch (m) {
  	case 0: return z;               /* atan(+,+) */
  	case 1: return -z;              /* atan(-,+) */
  	case 2: return 2*pio2_hi-(z-2*pio2_lo); /* atan(+,-) */
  	default: /* case 3 */
  		return (z-2*pio2_lo)-2*pio2_hi; /* atan(-,-) */
  	}
  }
  #endif
  