OpenLibm/src/s_atanf.c

/* s_atanf.c -- float version of s_atan.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 "cdefs-compat.h"
//__FBSDID("$FreeBSD: src/lib/msun/src/s_atanf.c,v 1.10 2008/08/01 01:24:25 das Exp $");

#include <openlibm_math.h>

#include "math_private.h"

static const float atanhi[] = {
  4.6364760399e-01, /* atan(0.5)hi 0x3eed6338 */
  7.8539812565e-01, /* atan(1.0)hi 0x3f490fda */
  9.8279368877e-01, /* atan(1.5)hi 0x3f7b985e */
  1.5707962513e+00, /* atan(inf)hi 0x3fc90fda */
};

static const float atanlo[] = {
  5.0121582440e-09, /* atan(0.5)lo 0x31ac3769 */
  3.7748947079e-08, /* atan(1.0)lo 0x33222168 */
  3.4473217170e-08, /* atan(1.5)lo 0x33140fb4 */
  7.5497894159e-08, /* atan(inf)lo 0x33a22168 */
};

static const float aT[] = {
  3.3333328366e-01,
 -1.9999158382e-01,
  1.4253635705e-01,
 -1.0648017377e-01,
  6.1687607318e-02,
};

static const float
one   = 1.0,
huge   = 1.0e30;

OLM_DLLEXPORT float
atanf(float x)
{
	float w,s1,s2,z;
	int32_t ix,hx,id;

	GET_FLOAT_WORD(hx,x);
	ix = hx&0x7fffffff;
	if(ix>=0x4c800000) {	/* if |x| >= 2**26 */
	    if(ix>0x7f800000)
		return x+x;		/* NaN */
	    if(hx>0) return  atanhi[3]+*(volatile float *)&atanlo[3];
	    else     return -atanhi[3]-*(volatile float *)&atanlo[3];
	} if (ix < 0x3ee00000) {	/* |x| < 0.4375 */
	    if (ix < 0x39800000) {	/* |x| < 2**-12 */
		if(huge+x>one) return x;	/* raise inexact */
	    }
	    id = -1;
	} else {
	x = fabsf(x);
	if (ix < 0x3f980000) {		/* |x| < 1.1875 */
	    if (ix < 0x3f300000) {	/* 7/16 <=|x|<11/16 */
		id = 0; x = ((float)2.0*x-one)/((float)2.0+x);
	    } else {			/* 11/16<=|x|< 19/16 */
		id = 1; x  = (x-one)/(x+one);
	    }
	} else {
	    if (ix < 0x401c0000) {	/* |x| < 2.4375 */
		id = 2; x  = (x-(float)1.5)/(one+(float)1.5*x);
	    } else {			/* 2.4375 <= |x| < 2**26 */
		id = 3; x  = -(float)1.0/x;
	    }
	}}
    /* end of argument reduction */
	z = x*x;
	w = z*z;
    /* break sum from i=0 to 10 aT[i]z**(i+1) into odd and even poly */
	s1 = z*(aT[0]+w*(aT[2]+w*aT[4]));
	s2 = w*(aT[1]+w*aT[3]);
	if (id<0) return x - x*(s1+s2);
	else {
	    z = atanhi[id] - ((x*(s1+s2) - atanlo[id]) - x);
	    return (hx<0)? -z:z;
	}
}