text: 
  /* @(#)e_atan2.c 1.3 95/01/18 */
  /* FreeBSD: head/lib/msun/src/e_atan2.c 176451 2008-02-22 02:30:36Z das */
  /*
   * ====================================================
   * 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.
   * ====================================================
   *
   */
  
  #include <sys/cdefs.h>
  #include <config/HaikuConfig.h>
  __FBSDID("$FreeBSD$");
  
  /*
   * See comments in e_atan2.c.
   * Converted to long double by David Schultz <das@FreeBSD.ORG>.
   */
  
  #include <float.h>
  
  #include "invtrig.h"
  #include "math.h"
  #include "math_private.h"
  
  static volatile long double
  tiny  = 1.0e-300;
  static const long double
  zero  = 0.0;
  
  #ifdef __HAIKU_ARCH_X86
  /* XXX Work around the fact that gcc truncates long double constants on i386 */
  static volatile double
  pi1 =  3.14159265358979311600e+00,	/*  0x1.921fb54442d18p+1  */
  pi2 =  1.22514845490862001043e-16;	/*  0x1.1a80000000000p-53 */
  #define	pi	((long double)pi1 + pi2)
  #else
  static const long double
  pi =  3.14159265358979323846264338327950280e+00L;
  #endif
  
  long double
  atan2l(long double y, long double x)
  {
  	union IEEEl2bits ux, uy;
  	long double z;
  	int32_t k,m;
  	int16_t exptx, expsignx, expty, expsigny;
  
  	uy.e = y;
  	expsigny = uy.xbits.expsign;
  	expty = expsigny & 0x7fff;
  	ux.e = x;
  	expsignx = ux.xbits.expsign;
  	exptx = expsignx & 0x7fff;
  
  	if ((exptx==BIAS+LDBL_MAX_EXP &&
  	     ((ux.bits.manh&~LDBL_NBIT)|ux.bits.manl)!=0) ||	/* x is NaN */
  	    (expty==BIAS+LDBL_MAX_EXP &&
  	     ((uy.bits.manh&~LDBL_NBIT)|uy.bits.manl)!=0))	/* y is NaN */
  	    return x+y;
  	if (expsignx==BIAS && ((ux.bits.manh&~LDBL_NBIT)|ux.bits.manl)==0)
  	    return atanl(y);					/* x=1.0 */
  	m = ((expsigny>>15)&1)|((expsignx>>14)&2);	/* 2*sign(x)+sign(y) */
  
      /* when y = 0 */
  	if(expty==0 && ((uy.bits.manh&~LDBL_NBIT)|uy.bits.manl)==0) {
  	    switch(m) {
  		case 0: 
  		case 1: return y; 	/* atan(+-0,+anything)=+-0 */
  		case 2: return  pi+tiny;/* atan(+0,-anything) = pi */
  		case 3: return -pi-tiny;/* atan(-0,-anything) =-pi */
  	    }
  	}
      /* when x = 0 */
  	if(exptx==0 && ((ux.bits.manh&~LDBL_NBIT)|ux.bits.manl)==0)
  	    return (expsigny<0)?  -pio2_hi-tiny: pio2_hi+tiny;
  
      /* when x is INF */
  	if(exptx==BIAS+LDBL_MAX_EXP) {
  	    if(expty==BIAS+LDBL_MAX_EXP) {
  		switch(m) {
  		    case 0: return  pio2_hi*0.5+tiny;/* atan(+INF,+INF) */
  		    case 1: return -pio2_hi*0.5-tiny;/* atan(-INF,+INF) */
  		    case 2: return  1.5*pio2_hi+tiny;/*atan(+INF,-INF)*/
  		    case 3: return -1.5*pio2_hi-tiny;/*atan(-INF,-INF)*/
  		}
  	    } else {
  		switch(m) {
  		    case 0: return  zero  ;	/* atan(+...,+INF) */
  		    case 1: return -zero  ;	/* atan(-...,+INF) */
  		    case 2: return  pi+tiny  ;	/* atan(+...,-INF) */
  		    case 3: return -pi-tiny  ;	/* atan(-...,-INF) */
  		}
  	    }
  	}
      /* when y is INF */
  	if(expty==BIAS+LDBL_MAX_EXP)
  	    return (expsigny<0)? -pio2_hi-tiny: pio2_hi+tiny;
  
      /* compute y/x */
  	k = expty-exptx;
  	if(k > LDBL_MANT_DIG+2) {			/* |y/x| huge */
  	    z=pio2_hi+pio2_lo;
  	    m&=1;
  	}
  	else if(expsignx<0&&k<-LDBL_MANT_DIG-2) z=0.0; 	/* |y/x| tiny, x<0 */
  	else z=atanl(fabsl(y/x));		/* safe to do 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(-,-) */
  	}
  }
  