4
* Copyright (c) 1998, 2004, Oracle and/or its affiliates. All rights reserved.
5
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
7
* This code is free software; you can redistribute it and/or modify it
8
* under the terms of the GNU General Public License version 2 only, as
9
* published by the Free Software Foundation. Oracle designates this
10
* particular file as subject to the "Classpath" exception as provided
11
* by Oracle in the LICENSE file that accompanied this code.
13
* This code is distributed in the hope that it will be useful, but WITHOUT
14
* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
15
* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
16
* version 2 for more details (a copy is included in the LICENSE file that
17
* accompanied this code).
19
* You should have received a copy of the GNU General Public License version
20
* 2 along with this work; if not, write to the Free Software Foundation,
21
* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
23
* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
24
* or visit www.oracle.com if you need additional information or have any
28
/* __ieee754_pow(x,y) return x**y
31
* Method: Let x = 2 * (1+f)
32
* 1. Compute and return log2(x) in two pieces:
34
* where w1 has 53-24 = 29 bit trailing zeros.
35
* 2. Perform y*log2(x) = n+y' by simulating muti-precision
36
* arithmetic, where |y'|<=0.5.
37
* 3. Return x**y = 2**n*exp(y'*log2)
40
* 1. (anything) ** 0 is 1
41
* 2. (anything) ** 1 is itself
42
* 3. (anything) ** NAN is NAN
43
* 4. NAN ** (anything except 0) is NAN
44
* 5. +-(|x| > 1) ** +INF is +INF
45
* 6. +-(|x| > 1) ** -INF is +0
46
* 7. +-(|x| < 1) ** +INF is +0
47
* 8. +-(|x| < 1) ** -INF is +INF
48
* 9. +-1 ** +-INF is NAN
49
* 10. +0 ** (+anything except 0, NAN) is +0
50
* 11. -0 ** (+anything except 0, NAN, odd integer) is +0
51
* 12. +0 ** (-anything except 0, NAN) is +INF
52
* 13. -0 ** (-anything except 0, NAN, odd integer) is +INF
53
* 14. -0 ** (odd integer) = -( +0 ** (odd integer) )
54
* 15. +INF ** (+anything except 0,NAN) is +INF
55
* 16. +INF ** (-anything except 0,NAN) is +0
56
* 17. -INF ** (anything) = -0 ** (-anything)
57
* 18. (-anything) ** (integer) is (-1)**(integer)*(+anything**integer)
58
* 19. (-anything except 0 and inf) ** (non-integer) is NAN
61
* pow(x,y) returns x**y nearly rounded. In particular
62
* pow(integer,integer)
63
* always returns the correct integer provided it is
67
* The hexadecimal values are the intended ones for the following
68
* constants. The decimal values may be used, provided that the
69
* compiler will convert from decimal to binary accurately enough
70
* to produce the hexadecimal values shown.
72
using unsigned = System.UInt32;
73
#pragma warning disable 168
75
static partial class fdlibm
77
static readonly double[] bp = {1.0, 1.5,};
78
static readonly double[] dp_h = { 0.0, 5.84962487220764160156e-01,}; /* 0x3FE2B803, 0x40000000 */
79
static readonly double[] dp_l = { 0.0, 1.35003920212974897128e-08,}; /* 0x3E4CFDEB, 0x43CFD006 */
81
internal static double __ieee754_pow(double x, double y)
83
const double zero = 0.0,
86
two53 = 9007199254740992.0, /* 0x43400000, 0x00000000 */
89
/* poly coefs for (3/2)*(log(x)-2s-2/3*s**3 */
90
L1 = 5.99999999999994648725e-01, /* 0x3FE33333, 0x33333303 */
91
L2 = 4.28571428578550184252e-01, /* 0x3FDB6DB6, 0xDB6FABFF */
92
L3 = 3.33333329818377432918e-01, /* 0x3FD55555, 0x518F264D */
93
L4 = 2.72728123808534006489e-01, /* 0x3FD17460, 0xA91D4101 */
94
L5 = 2.30660745775561754067e-01, /* 0x3FCD864A, 0x93C9DB65 */
95
L6 = 2.06975017800338417784e-01, /* 0x3FCA7E28, 0x4A454EEF */
96
P1 = 1.66666666666666019037e-01, /* 0x3FC55555, 0x5555553E */
97
P2 = -2.77777777770155933842e-03, /* 0xBF66C16C, 0x16BEBD93 */
98
P3 = 6.61375632143793436117e-05, /* 0x3F11566A, 0xAF25DE2C */
99
P4 = -1.65339022054652515390e-06, /* 0xBEBBBD41, 0xC5D26BF1 */
100
P5 = 4.13813679705723846039e-08, /* 0x3E663769, 0x72BEA4D0 */
101
lg2 = 6.93147180559945286227e-01, /* 0x3FE62E42, 0xFEFA39EF */
102
lg2_h = 6.93147182464599609375e-01, /* 0x3FE62E43, 0x00000000 */
103
lg2_l = -1.90465429995776804525e-09, /* 0xBE205C61, 0x0CA86C39 */
104
ovt = 8.0085662595372944372e-0017, /* -(1024-log2(ovfl+.5ulp)) */
105
cp = 9.61796693925975554329e-01, /* 0x3FEEC709, 0xDC3A03FD =2/(3ln2) */
106
cp_h = 9.61796700954437255859e-01, /* 0x3FEEC709, 0xE0000000 =(float)cp */
107
cp_l = -7.02846165095275826516e-09, /* 0xBE3E2FE0, 0x145B01F5 =tail of cp_h*/
108
ivln2 = 1.44269504088896338700e+00, /* 0x3FF71547, 0x652B82FE =1/ln2 */
109
ivln2_h = 1.44269502162933349609e+00, /* 0x3FF71547, 0x60000000 =24b 1/ln2*/
110
ivln2_l = 1.92596299112661746887e-08; /* 0x3E54AE0B, 0xF85DDF44 =1/ln2 tail*/
112
double z,ax,z_h,z_l,p_h,p_l;
113
double y1,t1,t2,r,s,t,u,v,w;
114
int i0,i1,i,j,k,yisint,n;
118
hx = __HI(x); lx = (uint)__LO(x);
119
hy = __HI(y); ly = (uint)__LO(y);
120
ix = hx&0x7fffffff; iy = hy&0x7fffffff;
122
/* y==zero: x**0 = 1 */
123
if((iy|(int)ly)==0) return one;
125
/* +-NaN return x+y */
126
if(ix > 0x7ff00000 || ((ix==0x7ff00000)&&(lx!=0)) ||
127
iy > 0x7ff00000 || ((iy==0x7ff00000)&&(ly!=0)))
130
/* determine if y is an odd int when x < 0
131
* yisint = 0 ... y is not an integer
132
* yisint = 1 ... y is an odd int
133
* yisint = 2 ... y is an even int
137
if(iy>=0x43400000) yisint = 2; /* even integer y */
138
else if(iy>=0x3ff00000) {
139
k = (iy>>20)-0x3ff; /* exponent */
141
j = (int)(ly>>(52-k));
142
if((j<<(52-k))==(int)ly) yisint = 2-(j&1);
145
if((j<<(20-k))==iy) yisint = 2-(j&1);
150
/* special value of y */
152
if (iy==0x7ff00000) { /* y is +-inf */
153
if(((ix-0x3ff00000)|(int)lx)==0)
154
return y - y; /* inf**+-1 is NaN */
155
else if (ix >= 0x3ff00000)/* (|x|>1)**+-inf = inf,0 */
156
return (hy>=0)? y: zero;
157
else /* (|x|<1)**-,+inf = inf,0 */
158
return (hy<0)?-y: zero;
160
if(iy==0x3ff00000) { /* y is +-1 */
161
if(hy<0) return one/x; else return x;
163
if(hy==0x40000000) return x*x; /* y is 2 */
164
if(hy==0x3fe00000) { /* y is 0.5 */
165
if(hx>=0) /* x >= +0 */
171
/* special value of x */
173
if(ix==0x7ff00000||ix==0||ix==0x3ff00000){
174
z = ax; /*x is +-0,+-inf,+-1*/
175
if(hy<0) z = one/z; /* z = (1/|x|) */
177
if(((ix-0x3ff00000)|yisint)==0) {
178
z = (z-z)/(z-z); /* (-1)**non-int is NaN */
180
z = -1.0*z; /* (x<0)**odd = -(|x|**odd) */
188
/* (x<0)**(non-int) is NaN */
189
if((n|yisint)==0) return (x-x)/(x-x);
191
s = one; /* s (sign of result -ve**odd) = -1 else = 1 */
192
if((n|(yisint-1))==0) s = -one;/* (-ve)**(odd int) */
195
if(iy>0x41e00000) { /* if |y| > 2**31 */
196
if(iy>0x43f00000){ /* if |y| > 2**64, must o/uflow */
197
if(ix<=0x3fefffff) return (hy<0)? huge*huge:tiny*tiny;
198
if(ix>=0x3ff00000) return (hy>0)? huge*huge:tiny*tiny;
200
/* over/underflow if x is not close to one */
201
if(ix<0x3fefffff) return (hy<0)? s*huge*huge:s*tiny*tiny;
202
if(ix>0x3ff00000) return (hy>0)? s*huge*huge:s*tiny*tiny;
203
/* now |1-x| is tiny <= 2**-20, suffice to compute
204
log(x) by x-x^2/2+x^3/3-x^4/4 */
205
t = ax-one; /* t has 20 trailing zeros */
206
w = (t*t)*(0.5-t*(0.3333333333333333333333-t*0.25));
207
u = ivln2_h*t; /* ivln2_h has 21 sig. bits */
208
v = t*ivln2_l-w*ivln2;
213
double ss,s2,s_h,s_l,t_h,t_l;
215
/* take care subnormal number */
217
{ax *= two53; n -= 53; ix = __HI(ax); }
218
n += ((ix)>>20)-0x3ff;
220
/* determine interval */
221
ix = j|0x3ff00000; /* normalize ix */
222
if(j<=0x3988E) k=0; /* |x|<sqrt(3/2) */
223
else if(j<0xBB67A) k=1; /* |x|<sqrt(3) */
224
else {k=0;n+=1;ix -= 0x00100000;}
227
/* compute ss = s_h+s_l = (x-1)/(x+1) or (x-1.5)/(x+1.5) */
228
u = ax-bp[k]; /* bp[0]=1.0, bp[1]=1.5 */
233
/* t_h=ax+bp[k] High */
235
t_h = __HI(t_h, ((ix >> 1) | 0x20000000) + 0x00080000 + (k << 18));
236
t_l = ax - (t_h-bp[k]);
237
s_l = v*((u-s_h*t_h)-s_h*t_l);
238
/* compute log(ax) */
240
r = s2*s2*(L1+s2*(L2+s2*(L3+s2*(L4+s2*(L5+s2*L6)))));
245
t_l = r-((t_h-3.0)-s2);
246
/* u+v = ss*(1+...) */
249
/* 2/(3log2)*(ss+...) */
253
z_h = cp_h*p_h; /* cp_h+cp_l = 2/(3*log2) */
254
z_l = cp_l*p_h+p_l*cp+dp_l[k];
255
/* log2(ax) = (ss+..)*2/(3*log2) = n + dp_h + z_h + z_l */
257
t1 = (((z_h+z_l)+dp_h[k])+t);
259
t2 = z_l-(((t1-t)-dp_h[k])-z_h);
262
/* split up y into y1+y2 and compute (y1+y2)*(t1+t2) */
265
p_l = (y-y1)*t1+y*t2;
270
if (j>=0x40900000) { /* z >= 1024 */
271
if(((j-0x40900000)|i)!=0) /* if z > 1024 */
272
return s*huge*huge; /* overflow */
274
if(p_l+ovt>z-p_h) return s*huge*huge; /* overflow */
276
} else if((j&0x7fffffff)>=0x4090cc00 ) { /* z <= -1075 */
277
if(((int)(j-0xc090cc00)|i)!=0) /* z < -1075 */
278
return s*tiny*tiny; /* underflow */
280
if(p_l<=z-p_h) return s*tiny*tiny; /* underflow */
284
* compute 2**(p_h+p_l)
289
if(i>0x3fe00000) { /* if |z| > 0.5, set n = [z+0.5] */
290
n = j+(0x00100000>>(k+1));
291
k = ((n&0x7fffffff)>>20)-0x3ff; /* new k for n */
293
t = __HI(t, (n&~(0x000fffff>>k)));
294
n = ((n&0x000fffff)|0x00100000)>>(20-k);
301
v = (p_l-(t-p_h))*lg2+t*lg2_l;
305
t1 = z - t*(P1+t*(P2+t*(P3+t*(P4+t*P5))));
306
r = (z*t1)/(t1-two)-(w+z*w);
310
if((j>>20)<=0) z = scalbn(z,n); /* subnormal output */
311
else z = __HI(z, __HI(z) + (n<<20));