1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
|
/* $OpenBSD: n_atan2.c,v 1.8 2008/06/21 08:26:19 martynas Exp $ */
/* $NetBSD: n_atan2.c,v 1.1 1995/10/10 23:36:37 ragge Exp $ */
/*
* Copyright (c) 1985, 1993
* The Regents of the University of California. All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
* 3. Neither the name of the University nor the names of its contributors
* may be used to endorse or promote products derived from this software
* without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
* SUCH DAMAGE.
*/
#ifndef lint
static char sccsid[] = "@(#)atan2.c 8.1 (Berkeley) 6/4/93";
#endif /* not lint */
/* ATAN2(Y,X)
* RETURN ARG (X+iY)
* DOUBLE PRECISION (VAX D format 56 bits, IEEE DOUBLE 53 BITS)
* CODED IN C BY K.C. NG, 1/8/85;
* REVISED BY K.C. NG on 2/7/85, 2/13/85, 3/7/85, 3/30/85, 6/29/85.
*
* Required system supported functions :
* copysign(x,y)
* scalbn(x,y)
* logb(x)
*
* Method :
* 1. Reduce y to positive by atan2(y,x)=-atan2(-y,x).
* 2. Reduce x to positive by (if x and y are unexceptional):
* ARG (x+iy) = arctan(y/x) ... if x > 0,
* ARG (x+iy) = pi - arctan[y/(-x)] ... if x < 0,
* 3. According to the integer k=4t+0.25 truncated , t=y/x, the argument
* is further reduced to one of the following intervals and the
* arctangent of y/x is evaluated by the corresponding formula:
*
* [0,7/16] atan(y/x) = t - t^3*(a1+t^2*(a2+...(a10+t^2*a11)...)
* [7/16,11/16] atan(y/x) = atan(1/2) + atan( (y-x/2)/(x+y/2) )
* [11/16.19/16] atan(y/x) = atan( 1 ) + atan( (y-x)/(x+y) )
* [19/16,39/16] atan(y/x) = atan(3/2) + atan( (y-1.5x)/(x+1.5y) )
* [39/16,INF] atan(y/x) = atan(INF) + atan( -x/y )
*
* Special cases:
* Notations: atan2(y,x) == ARG (x+iy) == ARG(x,y).
*
* ARG( NAN , (anything) ) is NaN;
* ARG( (anything), NaN ) is NaN;
* ARG(+(anything but NaN), +-0) is +-0 ;
* ARG(-(anything but NaN), +-0) is +-PI ;
* ARG( 0, +-(anything but 0 and NaN) ) is +-PI/2;
* ARG( +INF,+-(anything but INF and NaN) ) is +-0 ;
* ARG( -INF,+-(anything but INF and NaN) ) is +-PI;
* ARG( +INF,+-INF ) is +-PI/4 ;
* ARG( -INF,+-INF ) is +-3PI/4;
* ARG( (anything but,0,NaN, and INF),+-INF ) is +-PI/2;
*
* Accuracy:
* atan2(y,x) returns (PI/pi) * the exact ARG (x+iy) nearly rounded,
* where
*
* in decimal:
* pi = 3.141592653589793 23846264338327 .....
* 53 bits PI = 3.141592653589793 115997963 ..... ,
* 56 bits PI = 3.141592653589793 227020265 ..... ,
*
* in hexadecimal:
* pi = 3.243F6A8885A308D313198A2E....
* 53 bits PI = 3.243F6A8885A30 = 2 * 1.921FB54442D18 error=.276ulps
* 56 bits PI = 3.243F6A8885A308 = 4 * .C90FDAA22168C2 error=.206ulps
*
* In a test run with 356,000 random argument on [-1,1] * [-1,1] on a
* VAX, the maximum observed error was 1.41 ulps (units of the last place)
* compared with (PI/pi)*(the exact ARG(x+iy)).
*
* Note:
* We use machine PI (the true pi rounded) in place of the actual
* value of pi for all the trig and inverse trig functions. In general,
* if trig is one of sin, cos, tan, then computed trig(y) returns the
* exact trig(y*pi/PI) nearly rounded; correspondingly, computed arctrig
* returns the exact arctrig(y)*PI/pi nearly rounded. These guarantee the
* trig functions have period PI, and trig(arctrig(x)) returns x for
* all critical values x.
*
* Constants:
* The hexadecimal values are the intended ones for the following constants.
* The decimal values may be used, provided that the compiler will convert
* from decimal to binary accurately enough to produce the hexadecimal values
* shown.
*/
#include "math.h"
#include "mathimpl.h"
vc(athfhi, 4.6364760900080611433E-1 ,6338,3fed,da7b,2b0d, -1, .ED63382B0DDA7B)
vc(athflo, 1.9338828231967579916E-19 ,5005,2164,92c0,9cfe, -62, .E450059CFE92C0)
vc(PIo4, 7.8539816339744830676E-1 ,0fda,4049,68c2,a221, 0, .C90FDAA22168C2)
vc(at1fhi, 9.8279372324732906796E-1 ,985e,407b,b4d9,940f, 0, .FB985E940FB4D9)
vc(at1flo,-3.5540295636764633916E-18 ,1edc,a383,eaea,34d6, -57,-.831EDC34D6EAEA)
vc(PIo2, 1.5707963267948966135E0 ,0fda,40c9,68c2,a221, 1, .C90FDAA22168C2)
vc(PI, 3.1415926535897932270E0 ,0fda,4149,68c2,a221, 2, .C90FDAA22168C2)
vc(a1, 3.3333333333333473730E-1 ,aaaa,3faa,ab75,aaaa, -1, .AAAAAAAAAAAB75)
vc(a2, -2.0000000000017730678E-1 ,cccc,bf4c,946e,cccd, -2,-.CCCCCCCCCD946E)
vc(a3, 1.4285714286694640301E-1 ,4924,3f12,4262,9274, -2, .92492492744262)
vc(a4, -1.1111111135032672795E-1 ,8e38,bee3,6292,ebc6, -3,-.E38E38EBC66292)
vc(a5, 9.0909091380563043783E-2 ,2e8b,3eba,d70c,b31b, -3, .BA2E8BB31BD70C)
vc(a6, -7.6922954286089459397E-2 ,89c8,be9d,7f18,27c3, -3,-.9D89C827C37F18)
vc(a7, 6.6663180891693915586E-2 ,86b4,3e88,9e58,ae37, -3, .8886B4AE379E58)
vc(a8, -5.8772703698290408927E-2 ,bba5,be70,a942,8481, -4,-.F0BBA58481A942)
vc(a9, 5.2170707402812969804E-2 ,b0f3,3e55,13ab,a1ab, -4, .D5B0F3A1AB13AB)
vc(a10, -4.4895863157820361210E-2 ,e4b9,be37,048f,7fd1, -4,-.B7E4B97FD1048F)
vc(a11, 3.3006147437343875094E-2 ,3174,3e07,2d87,3cf7, -4, .8731743CF72D87)
vc(a12, -1.4614844866464185439E-2 ,731a,bd6f,76d9,2f34, -6,-.EF731A2F3476D9)
ic(athfhi, 4.6364760900080609352E-1 , -2, 1.DAC670561BB4F)
ic(athflo, 4.6249969567426939759E-18 , -58, 1.5543B8F253271)
ic(PIo4, 7.8539816339744827900E-1 , -1, 1.921FB54442D18)
ic(at1fhi, 9.8279372324732905408E-1 , -1, 1.F730BD281F69B)
ic(at1flo,-2.4407677060164810007E-17 , -56, -1.C23DFEFEAE6B5)
ic(PIo2, 1.5707963267948965580E0 , 0, 1.921FB54442D18)
ic(PI, 3.1415926535897931160E0 , 1, 1.921FB54442D18)
ic(a1, 3.3333333333333942106E-1 , -2, 1.55555555555C3)
ic(a2, -1.9999999999979536924E-1 , -3, -1.9999999997CCD)
ic(a3, 1.4285714278004377209E-1 , -3, 1.24924921EC1D7)
ic(a4, -1.1111110579344973814E-1 , -4, -1.C71C7059AF280)
ic(a5, 9.0908906105474668324E-2 , -4, 1.745CE5AA35DB2)
ic(a6, -7.6919217767468239799E-2 , -4, -1.3B0FA54BEC400)
ic(a7, 6.6614695906082474486E-2 , -4, 1.10DA924597FFF)
ic(a8, -5.8358371008508623523E-2 , -5, -1.DE125FDDBD793)
ic(a9, 4.9850617156082015213E-2 , -5, 1.9860524BDD807)
ic(a10, -3.6700606902093604877E-2 , -5, -1.2CA6C04C6937A)
ic(a11, 1.6438029044759730479E-2 , -6, 1.0D52174A1BB54)
#ifdef vccast
#define athfhi vccast(athfhi)
#define athflo vccast(athflo)
#define PIo4 vccast(PIo4)
#define at1fhi vccast(at1fhi)
#define at1flo vccast(at1flo)
#define PIo2 vccast(PIo2)
#define PI vccast(PI)
#define a1 vccast(a1)
#define a2 vccast(a2)
#define a3 vccast(a3)
#define a4 vccast(a4)
#define a5 vccast(a5)
#define a6 vccast(a6)
#define a7 vccast(a7)
#define a8 vccast(a8)
#define a9 vccast(a9)
#define a10 vccast(a10)
#define a11 vccast(a11)
#define a12 vccast(a12)
#endif
double
atan2(double y, double x)
{
static const double zero=0, one=1, small=1.0E-9, big=1.0E18;
double t,z,signy,signx,hi,lo;
int k,m;
/* if x or y is NAN */
if (isnan(x))
return (x);
if (isnan(y))
return (y);
/* copy down the sign of y and x */
signy = copysign(one,y) ;
signx = copysign(one,x) ;
/* if x is 1.0, goto begin */
if(x==1) { y=copysign(y,one); t=y; if(finite(t)) goto begin;}
/* when y = 0 */
if(y==zero) return((signx==one)?y:copysign(PI,signy));
/* when x = 0 */
if(x==zero) return(copysign(PIo2,signy));
/* when x is INF */
if(!finite(x))
if(!finite(y))
return(copysign((signx==one)?PIo4:3*PIo4,signy));
else
return(copysign((signx==one)?zero:PI,signy));
/* when y is INF */
if(!finite(y)) return(copysign(PIo2,signy));
/* compute y/x */
x=copysign(x,one);
y=copysign(y,one);
if((m=(k=logb(y))-logb(x)) > 60) t=big+big;
else if(m < -80 ) t=y/x;
else { t = y/x ; y = scalbn(y,-k); x=scalbn(x,-k); }
/* begin argument reduction */
begin:
if (t < 2.4375) {
/* truncate 4(t+1/16) to integer for branching */
k = 4 * (t+0.0625);
switch (k) {
/* t is in [0,7/16] */
case 0:
case 1:
if (t < small)
{ big + small ; /* raise inexact flag */
return (copysign((signx>zero)?t:PI-t,signy)); }
hi = zero; lo = zero; break;
/* t is in [7/16,11/16] */
case 2:
hi = athfhi; lo = athflo;
z = x+x;
t = ( (y+y) - x ) / ( z + y ); break;
/* t is in [11/16,19/16] */
case 3:
case 4:
hi = PIo4; lo = zero;
t = ( y - x ) / ( x + y ); break;
/* t is in [19/16,39/16] */
default:
hi = at1fhi; lo = at1flo;
z = y-x; y=y+y+y; t = x+x;
t = ( (z+z)-x ) / ( t + y ); break;
}
}
/* end of if (t < 2.4375) */
else
{
hi = PIo2; lo = zero;
/* t is in [2.4375, big] */
if (t <= big) t = - x / y;
/* t is in [big, INF] */
else
{ big+small; /* raise inexact flag */
t = zero; }
}
/* end of argument reduction */
/* compute atan(t) for t in [-.4375, .4375] */
z = t*t;
#if defined(__vax__)
z = t*(z*(a1+z*(a2+z*(a3+z*(a4+z*(a5+z*(a6+z*(a7+z*(a8+
z*(a9+z*(a10+z*(a11+z*a12))))))))))));
#else /* defined(__vax__) */
z = t*(z*(a1+z*(a2+z*(a3+z*(a4+z*(a5+z*(a6+z*(a7+z*(a8+
z*(a9+z*(a10+z*a11)))))))))));
#endif /* defined(__vax__) */
z = lo - z; z += t; z += hi;
return(copysign((signx>zero)?z:PI-z,signy));
}
|
