xref: /netbsd-src/external/gpl3/gcc.old/dist/libquadmath/math/acosq.c (revision 627f7eb200a4419d89b531d55fccd2ee3ffdcde0)
1*627f7eb2Smrg /*
2*627f7eb2Smrg  * ====================================================
3*627f7eb2Smrg  * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
4*627f7eb2Smrg  *
5*627f7eb2Smrg  * Developed at SunPro, a Sun Microsystems, Inc. business.
6*627f7eb2Smrg  * Permission to use, copy, modify, and distribute this
7*627f7eb2Smrg  * software is freely granted, provided that this notice
8*627f7eb2Smrg  * is preserved.
9*627f7eb2Smrg  * ====================================================
10*627f7eb2Smrg  */
11*627f7eb2Smrg 
12*627f7eb2Smrg /*
13*627f7eb2Smrg    Long double expansions are
14*627f7eb2Smrg    Copyright (C) 2001 Stephen L. Moshier <moshier@na-net.ornl.gov>
15*627f7eb2Smrg    and are incorporated herein by permission of the author.  The author
16*627f7eb2Smrg    reserves the right to distribute this material elsewhere under different
17*627f7eb2Smrg    copying permissions.  These modifications are distributed here under
18*627f7eb2Smrg    the following terms:
19*627f7eb2Smrg 
20*627f7eb2Smrg     This library is free software; you can redistribute it and/or
21*627f7eb2Smrg     modify it under the terms of the GNU Lesser General Public
22*627f7eb2Smrg     License as published by the Free Software Foundation; either
23*627f7eb2Smrg     version 2.1 of the License, or (at your option) any later version.
24*627f7eb2Smrg 
25*627f7eb2Smrg     This library is distributed in the hope that it will be useful,
26*627f7eb2Smrg     but WITHOUT ANY WARRANTY; without even the implied warranty of
27*627f7eb2Smrg     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
28*627f7eb2Smrg     Lesser General Public License for more details.
29*627f7eb2Smrg 
30*627f7eb2Smrg     You should have received a copy of the GNU Lesser General Public
31*627f7eb2Smrg     License along with this library; if not, see
32*627f7eb2Smrg     <http://www.gnu.org/licenses/>.  */
33*627f7eb2Smrg 
34*627f7eb2Smrg /* acosq(x)
35*627f7eb2Smrg  * Method :
36*627f7eb2Smrg  *      acos(x)  = pi/2 - asin(x)
37*627f7eb2Smrg  *      acos(-x) = pi/2 + asin(x)
38*627f7eb2Smrg  * For |x| <= 0.375
39*627f7eb2Smrg  *      acos(x) = pi/2 - asin(x)
40*627f7eb2Smrg  * Between .375 and .5 the approximation is
41*627f7eb2Smrg  *      acos(0.4375 + x) = acos(0.4375) + x P(x) / Q(x)
42*627f7eb2Smrg  * Between .5 and .625 the approximation is
43*627f7eb2Smrg  *      acos(0.5625 + x) = acos(0.5625) + x rS(x) / sS(x)
44*627f7eb2Smrg  * For x > 0.625,
45*627f7eb2Smrg  *      acos(x) = 2 asin(sqrt((1-x)/2))
46*627f7eb2Smrg  *      computed with an extended precision square root in the leading term.
47*627f7eb2Smrg  * For x < -0.625
48*627f7eb2Smrg  *      acos(x) = pi - 2 asin(sqrt((1-|x|)/2))
49*627f7eb2Smrg  *
50*627f7eb2Smrg  * Special cases:
51*627f7eb2Smrg  *      if x is NaN, return x itself;
52*627f7eb2Smrg  *      if |x|>1, return NaN with invalid signal.
53*627f7eb2Smrg  *
54*627f7eb2Smrg  * Functions needed: sqrtq.
55*627f7eb2Smrg  */
56*627f7eb2Smrg 
57*627f7eb2Smrg #include "quadmath-imp.h"
58*627f7eb2Smrg 
59*627f7eb2Smrg static const __float128
60*627f7eb2Smrg   one = 1,
61*627f7eb2Smrg   pio2_hi = 1.5707963267948966192313216916397514420986Q,
62*627f7eb2Smrg   pio2_lo = 4.3359050650618905123985220130216759843812E-35Q,
63*627f7eb2Smrg 
64*627f7eb2Smrg   /* acos(0.5625 + x) = acos(0.5625) + x rS(x) / sS(x)
65*627f7eb2Smrg      -0.0625 <= x <= 0.0625
66*627f7eb2Smrg      peak relative error 3.3e-35  */
67*627f7eb2Smrg 
68*627f7eb2Smrg   rS0 =  5.619049346208901520945464704848780243887E0Q,
69*627f7eb2Smrg   rS1 = -4.460504162777731472539175700169871920352E1Q,
70*627f7eb2Smrg   rS2 =  1.317669505315409261479577040530751477488E2Q,
71*627f7eb2Smrg   rS3 = -1.626532582423661989632442410808596009227E2Q,
72*627f7eb2Smrg   rS4 =  3.144806644195158614904369445440583873264E1Q,
73*627f7eb2Smrg   rS5 =  9.806674443470740708765165604769099559553E1Q,
74*627f7eb2Smrg   rS6 = -5.708468492052010816555762842394927806920E1Q,
75*627f7eb2Smrg   rS7 = -1.396540499232262112248553357962639431922E1Q,
76*627f7eb2Smrg   rS8 =  1.126243289311910363001762058295832610344E1Q,
77*627f7eb2Smrg   rS9 =  4.956179821329901954211277873774472383512E-1Q,
78*627f7eb2Smrg   rS10 = -3.313227657082367169241333738391762525780E-1Q,
79*627f7eb2Smrg 
80*627f7eb2Smrg   sS0 = -4.645814742084009935700221277307007679325E0Q,
81*627f7eb2Smrg   sS1 =  3.879074822457694323970438316317961918430E1Q,
82*627f7eb2Smrg   sS2 = -1.221986588013474694623973554726201001066E2Q,
83*627f7eb2Smrg   sS3 =  1.658821150347718105012079876756201905822E2Q,
84*627f7eb2Smrg   sS4 = -4.804379630977558197953176474426239748977E1Q,
85*627f7eb2Smrg   sS5 = -1.004296417397316948114344573811562952793E2Q,
86*627f7eb2Smrg   sS6 =  7.530281592861320234941101403870010111138E1Q,
87*627f7eb2Smrg   sS7 =  1.270735595411673647119592092304357226607E1Q,
88*627f7eb2Smrg   sS8 = -1.815144839646376500705105967064792930282E1Q,
89*627f7eb2Smrg   sS9 = -7.821597334910963922204235247786840828217E-2Q,
90*627f7eb2Smrg   /* 1.000000000000000000000000000000000000000E0 */
91*627f7eb2Smrg 
92*627f7eb2Smrg   acosr5625 = 9.7338991014954640492751132535550279812151E-1Q,
93*627f7eb2Smrg   pimacosr5625 = 2.1682027434402468335351320579240000860757E0Q,
94*627f7eb2Smrg 
95*627f7eb2Smrg   /* acos(0.4375 + x) = acos(0.4375) + x rS(x) / sS(x)
96*627f7eb2Smrg      -0.0625 <= x <= 0.0625
97*627f7eb2Smrg      peak relative error 2.1e-35  */
98*627f7eb2Smrg 
99*627f7eb2Smrg   P0 =  2.177690192235413635229046633751390484892E0Q,
100*627f7eb2Smrg   P1 = -2.848698225706605746657192566166142909573E1Q,
101*627f7eb2Smrg   P2 =  1.040076477655245590871244795403659880304E2Q,
102*627f7eb2Smrg   P3 = -1.400087608918906358323551402881238180553E2Q,
103*627f7eb2Smrg   P4 =  2.221047917671449176051896400503615543757E1Q,
104*627f7eb2Smrg   P5 =  9.643714856395587663736110523917499638702E1Q,
105*627f7eb2Smrg   P6 = -5.158406639829833829027457284942389079196E1Q,
106*627f7eb2Smrg   P7 = -1.578651828337585944715290382181219741813E1Q,
107*627f7eb2Smrg   P8 =  1.093632715903802870546857764647931045906E1Q,
108*627f7eb2Smrg   P9 =  5.448925479898460003048760932274085300103E-1Q,
109*627f7eb2Smrg   P10 = -3.315886001095605268470690485170092986337E-1Q,
110*627f7eb2Smrg   Q0 = -1.958219113487162405143608843774587557016E0Q,
111*627f7eb2Smrg   Q1 =  2.614577866876185080678907676023269360520E1Q,
112*627f7eb2Smrg   Q2 = -9.990858606464150981009763389881793660938E1Q,
113*627f7eb2Smrg   Q3 =  1.443958741356995763628660823395334281596E2Q,
114*627f7eb2Smrg   Q4 = -3.206441012484232867657763518369723873129E1Q,
115*627f7eb2Smrg   Q5 = -1.048560885341833443564920145642588991492E2Q,
116*627f7eb2Smrg   Q6 =  6.745883931909770880159915641984874746358E1Q,
117*627f7eb2Smrg   Q7 =  1.806809656342804436118449982647641392951E1Q,
118*627f7eb2Smrg   Q8 = -1.770150690652438294290020775359580915464E1Q,
119*627f7eb2Smrg   Q9 = -5.659156469628629327045433069052560211164E-1Q,
120*627f7eb2Smrg   /* 1.000000000000000000000000000000000000000E0 */
121*627f7eb2Smrg 
122*627f7eb2Smrg   acosr4375 = 1.1179797320499710475919903296900511518755E0Q,
123*627f7eb2Smrg   pimacosr4375 = 2.0236129215398221908706530535894517323217E0Q,
124*627f7eb2Smrg 
125*627f7eb2Smrg   /* asin(x) = x + x^3 pS(x^2) / qS(x^2)
126*627f7eb2Smrg      0 <= x <= 0.5
127*627f7eb2Smrg      peak relative error 1.9e-35  */
128*627f7eb2Smrg   pS0 = -8.358099012470680544198472400254596543711E2Q,
129*627f7eb2Smrg   pS1 =  3.674973957689619490312782828051860366493E3Q,
130*627f7eb2Smrg   pS2 = -6.730729094812979665807581609853656623219E3Q,
131*627f7eb2Smrg   pS3 =  6.643843795209060298375552684423454077633E3Q,
132*627f7eb2Smrg   pS4 = -3.817341990928606692235481812252049415993E3Q,
133*627f7eb2Smrg   pS5 =  1.284635388402653715636722822195716476156E3Q,
134*627f7eb2Smrg   pS6 = -2.410736125231549204856567737329112037867E2Q,
135*627f7eb2Smrg   pS7 =  2.219191969382402856557594215833622156220E1Q,
136*627f7eb2Smrg   pS8 = -7.249056260830627156600112195061001036533E-1Q,
137*627f7eb2Smrg   pS9 =  1.055923570937755300061509030361395604448E-3Q,
138*627f7eb2Smrg 
139*627f7eb2Smrg   qS0 = -5.014859407482408326519083440151745519205E3Q,
140*627f7eb2Smrg   qS1 =  2.430653047950480068881028451580393430537E4Q,
141*627f7eb2Smrg   qS2 = -4.997904737193653607449250593976069726962E4Q,
142*627f7eb2Smrg   qS3 =  5.675712336110456923807959930107347511086E4Q,
143*627f7eb2Smrg   qS4 = -3.881523118339661268482937768522572588022E4Q,
144*627f7eb2Smrg   qS5 =  1.634202194895541569749717032234510811216E4Q,
145*627f7eb2Smrg   qS6 = -4.151452662440709301601820849901296953752E3Q,
146*627f7eb2Smrg   qS7 =  5.956050864057192019085175976175695342168E2Q,
147*627f7eb2Smrg   qS8 = -4.175375777334867025769346564600396877176E1Q;
148*627f7eb2Smrg   /* 1.000000000000000000000000000000000000000E0 */
149*627f7eb2Smrg 
150*627f7eb2Smrg __float128
acosq(__float128 x)151*627f7eb2Smrg acosq (__float128 x)
152*627f7eb2Smrg {
153*627f7eb2Smrg   __float128 z, r, w, p, q, s, t, f2;
154*627f7eb2Smrg   int32_t ix, sign;
155*627f7eb2Smrg   ieee854_float128 u;
156*627f7eb2Smrg 
157*627f7eb2Smrg   u.value = x;
158*627f7eb2Smrg   sign = u.words32.w0;
159*627f7eb2Smrg   ix = sign & 0x7fffffff;
160*627f7eb2Smrg   u.words32.w0 = ix;		/* |x| */
161*627f7eb2Smrg   if (ix >= 0x3fff0000)		/* |x| >= 1 */
162*627f7eb2Smrg     {
163*627f7eb2Smrg       if (ix == 0x3fff0000
164*627f7eb2Smrg 	  && (u.words32.w1 | u.words32.w2 | u.words32.w3) == 0)
165*627f7eb2Smrg 	{			/* |x| == 1 */
166*627f7eb2Smrg 	  if ((sign & 0x80000000) == 0)
167*627f7eb2Smrg 	    return 0.0;		/* acos(1) = 0  */
168*627f7eb2Smrg 	  else
169*627f7eb2Smrg 	    return (2.0 * pio2_hi) + (2.0 * pio2_lo);	/* acos(-1)= pi */
170*627f7eb2Smrg 	}
171*627f7eb2Smrg       return (x - x) / (x - x);	/* acos(|x| > 1) is NaN */
172*627f7eb2Smrg     }
173*627f7eb2Smrg   else if (ix < 0x3ffe0000)	/* |x| < 0.5 */
174*627f7eb2Smrg     {
175*627f7eb2Smrg       if (ix < 0x3f8e0000)	/* |x| < 2**-113 */
176*627f7eb2Smrg 	return pio2_hi + pio2_lo;
177*627f7eb2Smrg       if (ix < 0x3ffde000)	/* |x| < .4375 */
178*627f7eb2Smrg 	{
179*627f7eb2Smrg 	  /* Arcsine of x.  */
180*627f7eb2Smrg 	  z = x * x;
181*627f7eb2Smrg 	  p = (((((((((pS9 * z
182*627f7eb2Smrg 		       + pS8) * z
183*627f7eb2Smrg 		      + pS7) * z
184*627f7eb2Smrg 		     + pS6) * z
185*627f7eb2Smrg 		    + pS5) * z
186*627f7eb2Smrg 		   + pS4) * z
187*627f7eb2Smrg 		  + pS3) * z
188*627f7eb2Smrg 		 + pS2) * z
189*627f7eb2Smrg 		+ pS1) * z
190*627f7eb2Smrg 	       + pS0) * z;
191*627f7eb2Smrg 	  q = (((((((( z
192*627f7eb2Smrg 		       + qS8) * z
193*627f7eb2Smrg 		     + qS7) * z
194*627f7eb2Smrg 		    + qS6) * z
195*627f7eb2Smrg 		   + qS5) * z
196*627f7eb2Smrg 		  + qS4) * z
197*627f7eb2Smrg 		 + qS3) * z
198*627f7eb2Smrg 		+ qS2) * z
199*627f7eb2Smrg 	       + qS1) * z
200*627f7eb2Smrg 	    + qS0;
201*627f7eb2Smrg 	  r = x + x * p / q;
202*627f7eb2Smrg 	  z = pio2_hi - (r - pio2_lo);
203*627f7eb2Smrg 	  return z;
204*627f7eb2Smrg 	}
205*627f7eb2Smrg       /* .4375 <= |x| < .5 */
206*627f7eb2Smrg       t = u.value - 0.4375Q;
207*627f7eb2Smrg       p = ((((((((((P10 * t
208*627f7eb2Smrg 		    + P9) * t
209*627f7eb2Smrg 		   + P8) * t
210*627f7eb2Smrg 		  + P7) * t
211*627f7eb2Smrg 		 + P6) * t
212*627f7eb2Smrg 		+ P5) * t
213*627f7eb2Smrg 	       + P4) * t
214*627f7eb2Smrg 	      + P3) * t
215*627f7eb2Smrg 	     + P2) * t
216*627f7eb2Smrg 	    + P1) * t
217*627f7eb2Smrg 	   + P0) * t;
218*627f7eb2Smrg 
219*627f7eb2Smrg       q = (((((((((t
220*627f7eb2Smrg 		   + Q9) * t
221*627f7eb2Smrg 		  + Q8) * t
222*627f7eb2Smrg 		 + Q7) * t
223*627f7eb2Smrg 		+ Q6) * t
224*627f7eb2Smrg 	       + Q5) * t
225*627f7eb2Smrg 	      + Q4) * t
226*627f7eb2Smrg 	     + Q3) * t
227*627f7eb2Smrg 	    + Q2) * t
228*627f7eb2Smrg 	   + Q1) * t
229*627f7eb2Smrg 	+ Q0;
230*627f7eb2Smrg       r = p / q;
231*627f7eb2Smrg       if (sign & 0x80000000)
232*627f7eb2Smrg 	r = pimacosr4375 - r;
233*627f7eb2Smrg       else
234*627f7eb2Smrg 	r = acosr4375 + r;
235*627f7eb2Smrg       return r;
236*627f7eb2Smrg     }
237*627f7eb2Smrg   else if (ix < 0x3ffe4000)	/* |x| < 0.625 */
238*627f7eb2Smrg     {
239*627f7eb2Smrg       t = u.value - 0.5625Q;
240*627f7eb2Smrg       p = ((((((((((rS10 * t
241*627f7eb2Smrg 		    + rS9) * t
242*627f7eb2Smrg 		   + rS8) * t
243*627f7eb2Smrg 		  + rS7) * t
244*627f7eb2Smrg 		 + rS6) * t
245*627f7eb2Smrg 		+ rS5) * t
246*627f7eb2Smrg 	       + rS4) * t
247*627f7eb2Smrg 	      + rS3) * t
248*627f7eb2Smrg 	     + rS2) * t
249*627f7eb2Smrg 	    + rS1) * t
250*627f7eb2Smrg 	   + rS0) * t;
251*627f7eb2Smrg 
252*627f7eb2Smrg       q = (((((((((t
253*627f7eb2Smrg 		   + sS9) * t
254*627f7eb2Smrg 		  + sS8) * t
255*627f7eb2Smrg 		 + sS7) * t
256*627f7eb2Smrg 		+ sS6) * t
257*627f7eb2Smrg 	       + sS5) * t
258*627f7eb2Smrg 	      + sS4) * t
259*627f7eb2Smrg 	     + sS3) * t
260*627f7eb2Smrg 	    + sS2) * t
261*627f7eb2Smrg 	   + sS1) * t
262*627f7eb2Smrg 	+ sS0;
263*627f7eb2Smrg       if (sign & 0x80000000)
264*627f7eb2Smrg 	r = pimacosr5625 - p / q;
265*627f7eb2Smrg       else
266*627f7eb2Smrg 	r = acosr5625 + p / q;
267*627f7eb2Smrg       return r;
268*627f7eb2Smrg     }
269*627f7eb2Smrg   else
270*627f7eb2Smrg     {				/* |x| >= .625 */
271*627f7eb2Smrg       z = (one - u.value) * 0.5;
272*627f7eb2Smrg       s = sqrtq (z);
273*627f7eb2Smrg       /* Compute an extended precision square root from
274*627f7eb2Smrg 	 the Newton iteration  s -> 0.5 * (s + z / s).
275*627f7eb2Smrg 	 The change w from s to the improved value is
276*627f7eb2Smrg 	    w = 0.5 * (s + z / s) - s  = (s^2 + z)/2s - s = (z - s^2)/2s.
277*627f7eb2Smrg 	  Express s = f1 + f2 where f1 * f1 is exactly representable.
278*627f7eb2Smrg 	  w = (z - s^2)/2s = (z - f1^2 - 2 f1 f2 - f2^2)/2s .
279*627f7eb2Smrg 	  s + w has extended precision.  */
280*627f7eb2Smrg       u.value = s;
281*627f7eb2Smrg       u.words32.w2 = 0;
282*627f7eb2Smrg       u.words32.w3 = 0;
283*627f7eb2Smrg       f2 = s - u.value;
284*627f7eb2Smrg       w = z - u.value * u.value;
285*627f7eb2Smrg       w = w - 2.0 * u.value * f2;
286*627f7eb2Smrg       w = w - f2 * f2;
287*627f7eb2Smrg       w = w / (2.0 * s);
288*627f7eb2Smrg       /* Arcsine of s.  */
289*627f7eb2Smrg       p = (((((((((pS9 * z
290*627f7eb2Smrg 		   + pS8) * z
291*627f7eb2Smrg 		  + pS7) * z
292*627f7eb2Smrg 		 + pS6) * z
293*627f7eb2Smrg 		+ pS5) * z
294*627f7eb2Smrg 	       + pS4) * z
295*627f7eb2Smrg 	      + pS3) * z
296*627f7eb2Smrg 	     + pS2) * z
297*627f7eb2Smrg 	    + pS1) * z
298*627f7eb2Smrg 	   + pS0) * z;
299*627f7eb2Smrg       q = (((((((( z
300*627f7eb2Smrg 		   + qS8) * z
301*627f7eb2Smrg 		 + qS7) * z
302*627f7eb2Smrg 		+ qS6) * z
303*627f7eb2Smrg 	       + qS5) * z
304*627f7eb2Smrg 	      + qS4) * z
305*627f7eb2Smrg 	     + qS3) * z
306*627f7eb2Smrg 	    + qS2) * z
307*627f7eb2Smrg 	   + qS1) * z
308*627f7eb2Smrg 	+ qS0;
309*627f7eb2Smrg       r = s + (w + s * p / q);
310*627f7eb2Smrg 
311*627f7eb2Smrg       if (sign & 0x80000000)
312*627f7eb2Smrg 	w = pio2_hi + (pio2_lo - r);
313*627f7eb2Smrg       else
314*627f7eb2Smrg 	w = r;
315*627f7eb2Smrg       return 2.0 * w;
316*627f7eb2Smrg     }
317*627f7eb2Smrg }
318