s_atanf.c revision 97413 
1/* s_atanf.c -- float version of s_atan.c.
2 * Conversion to float by Ian Lance Taylor, Cygnus Support, ian@cygnus.com.
3 */
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#ifndef lint
17static char rcsid[] = "$FreeBSD: head/lib/msun/src/s_atanf.c 97413 2002-05-28 18:15:04Z alfred $";
18#endif
19
20#include "math.h"
21#include "math_private.h"
22
23static const float atanhi[] = {
24  4.6364760399e-01, /* atan(0.5)hi 0x3eed6338 */
25  7.8539812565e-01, /* atan(1.0)hi 0x3f490fda */
26  9.8279368877e-01, /* atan(1.5)hi 0x3f7b985e */
27  1.5707962513e+00, /* atan(inf)hi 0x3fc90fda */
28};
29
30static const float atanlo[] = {
31  5.0121582440e-09, /* atan(0.5)lo 0x31ac3769 */
32  3.7748947079e-08, /* atan(1.0)lo 0x33222168 */
33  3.4473217170e-08, /* atan(1.5)lo 0x33140fb4 */
34  7.5497894159e-08, /* atan(inf)lo 0x33a22168 */
35};
36
37static const float aT[] = {
38  3.3333334327e-01, /* 0x3eaaaaaa */
39 -2.0000000298e-01, /* 0xbe4ccccd */
40  1.4285714924e-01, /* 0x3e124925 */
41 -1.1111110449e-01, /* 0xbde38e38 */
42  9.0908870101e-02, /* 0x3dba2e6e */
43 -7.6918758452e-02, /* 0xbd9d8795 */
44  6.6610731184e-02, /* 0x3d886b35 */
45 -5.8335702866e-02, /* 0xbd6ef16b */
46  4.9768779427e-02, /* 0x3d4bda59 */
47 -3.6531571299e-02, /* 0xbd15a221 */
48  1.6285819933e-02, /* 0x3c8569d7 */
49};
50
51	static const float
52one   = 1.0,
53huge   = 1.0e30;
54
55float
56atanf(float x)
57{
58	float w,s1,s2,z;
59	int32_t ix,hx,id;
60
61	GET_FLOAT_WORD(hx,x);
62	ix = hx&0x7fffffff;
63	if(ix>=0x50800000) {	/* if |x| >= 2^34 */
64	    if(ix>0x7f800000)
65		return x+x;		/* NaN */
66	    if(hx>0) return  atanhi[3]+atanlo[3];
67	    else     return -atanhi[3]-atanlo[3];
68	} if (ix < 0x3ee00000) {	/* |x| < 0.4375 */
69	    if (ix < 0x31000000) {	/* |x| < 2^-29 */
70		if(huge+x>one) return x;	/* raise inexact */
71	    }
72	    id = -1;
73	} else {
74	x = fabsf(x);
75	if (ix < 0x3f980000) {		/* |x| < 1.1875 */
76	    if (ix < 0x3f300000) {	/* 7/16 <=|x|<11/16 */
77		id = 0; x = ((float)2.0*x-one)/((float)2.0+x);
78	    } else {			/* 11/16<=|x|< 19/16 */
79		id = 1; x  = (x-one)/(x+one);
80	    }
81	} else {
82	    if (ix < 0x401c0000) {	/* |x| < 2.4375 */
83		id = 2; x  = (x-(float)1.5)/(one+(float)1.5*x);
84	    } else {			/* 2.4375 <= |x| < 2^66 */
85		id = 3; x  = -(float)1.0/x;
86	    }
87	}}
88    /* end of argument reduction */
89	z = x*x;
90	w = z*z;
91    /* break sum from i=0 to 10 aT[i]z**(i+1) into odd and even poly */
92	s1 = z*(aT[0]+w*(aT[2]+w*(aT[4]+w*(aT[6]+w*(aT[8]+w*aT[10])))));
93	s2 = w*(aT[1]+w*(aT[3]+w*(aT[5]+w*(aT[7]+w*aT[9]))));
94	if (id<0) return x - x*(s1+s2);
95	else {
96	    z = atanhi[id] - ((x*(s1+s2) - atanlo[id]) - x);
97	    return (hx<0)? -z:z;
98	}
99}
100