1 /* e_powf.c -- float version of e_pow.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 #include <sys/cdefs.h>
17 __FBSDID("$FreeBSD$");
18
19 #include "math.h"
20 #include "math_private.h"
21
22 static const float
23 bp[] = {1.0, 1.5,},
24 dp_h[] = { 0.0, 5.84960938e-01,}, /* 0x3f15c000 */
25 dp_l[] = { 0.0, 1.56322085e-06,}, /* 0x35d1cfdc */
26 zero = 0.0,
27 one = 1.0,
28 two = 2.0,
29 two24 = 16777216.0, /* 0x4b800000 */
30 huge = 1.0e30,
31 tiny = 1.0e-30,
32 /* poly coefs for (3/2)*(log(x)-2s-2/3*s**3 */
33 L1 = 6.0000002384e-01, /* 0x3f19999a */
34 L2 = 4.2857143283e-01, /* 0x3edb6db7 */
35 L3 = 3.3333334327e-01, /* 0x3eaaaaab */
36 L4 = 2.7272811532e-01, /* 0x3e8ba305 */
37 L5 = 2.3066075146e-01, /* 0x3e6c3255 */
38 L6 = 2.0697501302e-01, /* 0x3e53f142 */
39 P1 = 1.6666667163e-01, /* 0x3e2aaaab */
40 P2 = -2.7777778450e-03, /* 0xbb360b61 */
41 P3 = 6.6137559770e-05, /* 0x388ab355 */
42 P4 = -1.6533901999e-06, /* 0xb5ddea0e */
43 P5 = 4.1381369442e-08, /* 0x3331bb4c */
44 lg2 = 6.9314718246e-01, /* 0x3f317218 */
45 lg2_h = 6.93145752e-01, /* 0x3f317200 */
46 lg2_l = 1.42860654e-06, /* 0x35bfbe8c */
47 ovt = 4.2995665694e-08, /* -(128-log2(ovfl+.5ulp)) */
48 cp = 9.6179670095e-01, /* 0x3f76384f =2/(3ln2) */
49 cp_h = 9.6191406250e-01, /* 0x3f764000 =12b cp */
50 cp_l = -1.1736857402e-04, /* 0xb8f623c6 =tail of cp_h */
51 ivln2 = 1.4426950216e+00, /* 0x3fb8aa3b =1/ln2 */
52 ivln2_h = 1.4426879883e+00, /* 0x3fb8aa00 =16b 1/ln2*/
53 ivln2_l = 7.0526075433e-06; /* 0x36eca570 =1/ln2 tail*/
54
55 float
__ieee754_powf(float x,float y)56 __ieee754_powf(float x, float y)
57 {
58 float z,ax,z_h,z_l,p_h,p_l;
59 float y1,t1,t2,r,s,sn,t,u,v,w;
60 int32_t i,j,k,yisint,n;
61 int32_t hx,hy,ix,iy,is;
62
63 GET_FLOAT_WORD(hx,x);
64 GET_FLOAT_WORD(hy,y);
65 ix = hx&0x7fffffff; iy = hy&0x7fffffff;
66
67 /* y==zero: x**0 = 1 */
68 if(iy==0) return one;
69
70 /* x==1: 1**y = 1, even if y is NaN */
71 if (hx==0x3f800000) return one;
72
73 /* y!=zero: result is NaN if either arg is NaN */
74 if(ix > 0x7f800000 ||
75 iy > 0x7f800000)
76 return (x+0.0F)+(y+0.0F);
77
78 /* determine if y is an odd int when x < 0
79 * yisint = 0 ... y is not an integer
80 * yisint = 1 ... y is an odd int
81 * yisint = 2 ... y is an even int
82 */
83 yisint = 0;
84 if(hx<0) {
85 if(iy>=0x4b800000) yisint = 2; /* even integer y */
86 else if(iy>=0x3f800000) {
87 k = (iy>>23)-0x7f; /* exponent */
88 j = iy>>(23-k);
89 if((j<<(23-k))==iy) yisint = 2-(j&1);
90 }
91 }
92
93 /* special value of y */
94 if (iy==0x7f800000) { /* y is +-inf */
95 if (ix==0x3f800000)
96 return one; /* (-1)**+-inf is NaN */
97 else if (ix > 0x3f800000)/* (|x|>1)**+-inf = inf,0 */
98 return (hy>=0)? y: zero;
99 else /* (|x|<1)**-,+inf = inf,0 */
100 return (hy<0)?-y: zero;
101 }
102 if(iy==0x3f800000) { /* y is +-1 */
103 if(hy<0) return one/x; else return x;
104 }
105 if(hy==0x40000000) return x*x; /* y is 2 */
106 if(hy==0x3f000000) { /* y is 0.5 */
107 if(hx>=0) /* x >= +0 */
108 return __ieee754_sqrtf(x);
109 }
110
111 ax = fabsf(x);
112 /* special value of x */
113 if(ix==0x7f800000||ix==0||ix==0x3f800000){
114 z = ax; /*x is +-0,+-inf,+-1*/
115 if(hy<0) z = one/z; /* z = (1/|x|) */
116 if(hx<0) {
117 if(((ix-0x3f800000)|yisint)==0) {
118 z = (z-z)/(z-z); /* (-1)**non-int is NaN */
119 } else if(yisint==1)
120 z = -z; /* (x<0)**odd = -(|x|**odd) */
121 }
122 return z;
123 }
124
125 n = ((u_int32_t)hx>>31)-1;
126
127 /* (x<0)**(non-int) is NaN */
128 if((n|yisint)==0) return (x-x)/(x-x);
129
130 sn = one; /* s (sign of result -ve**odd) = -1 else = 1 */
131 if((n|(yisint-1))==0) sn = -one;/* (-ve)**(odd int) */
132
133 /* |y| is huge */
134 if(iy>0x4d000000) { /* if |y| > 2**27 */
135 /* over/underflow if x is not close to one */
136 if(ix<0x3f7ffff8) return (hy<0)? sn*huge*huge:sn*tiny*tiny;
137 if(ix>0x3f800007) return (hy>0)? sn*huge*huge:sn*tiny*tiny;
138 /* now |1-x| is tiny <= 2**-20, suffice to compute
139 log(x) by x-x^2/2+x^3/3-x^4/4 */
140 t = ax-1; /* t has 20 trailing zeros */
141 w = (t*t)*((float)0.5-t*((float)0.333333333333-t*(float)0.25));
142 u = ivln2_h*t; /* ivln2_h has 16 sig. bits */
143 v = t*ivln2_l-w*ivln2;
144 t1 = u+v;
145 GET_FLOAT_WORD(is,t1);
146 SET_FLOAT_WORD(t1,is&0xfffff000);
147 t2 = v-(t1-u);
148 } else {
149 float s2,s_h,s_l,t_h,t_l;
150 n = 0;
151 /* take care subnormal number */
152 if(ix<0x00800000)
153 {ax *= two24; n -= 24; GET_FLOAT_WORD(ix,ax); }
154 n += ((ix)>>23)-0x7f;
155 j = ix&0x007fffff;
156 /* determine interval */
157 ix = j|0x3f800000; /* normalize ix */
158 if(j<=0x1cc471) k=0; /* |x|<sqrt(3/2) */
159 else if(j<0x5db3d7) k=1; /* |x|<sqrt(3) */
160 else {k=0;n+=1;ix -= 0x00800000;}
161 SET_FLOAT_WORD(ax,ix);
162
163 /* compute s = s_h+s_l = (x-1)/(x+1) or (x-1.5)/(x+1.5) */
164 u = ax-bp[k]; /* bp[0]=1.0, bp[1]=1.5 */
165 v = one/(ax+bp[k]);
166 s = u*v;
167 s_h = s;
168 GET_FLOAT_WORD(is,s_h);
169 SET_FLOAT_WORD(s_h,is&0xfffff000);
170 /* t_h=ax+bp[k] High */
171 is = ((ix>>1)&0xfffff000)|0x20000000;
172 SET_FLOAT_WORD(t_h,is+0x00400000+(k<<21));
173 t_l = ax - (t_h-bp[k]);
174 s_l = v*((u-s_h*t_h)-s_h*t_l);
175 /* compute log(ax) */
176 s2 = s*s;
177 r = s2*s2*(L1+s2*(L2+s2*(L3+s2*(L4+s2*(L5+s2*L6)))));
178 r += s_l*(s_h+s);
179 s2 = s_h*s_h;
180 t_h = (float)3.0+s2+r;
181 GET_FLOAT_WORD(is,t_h);
182 SET_FLOAT_WORD(t_h,is&0xfffff000);
183 t_l = r-((t_h-(float)3.0)-s2);
184 /* u+v = s*(1+...) */
185 u = s_h*t_h;
186 v = s_l*t_h+t_l*s;
187 /* 2/(3log2)*(s+...) */
188 p_h = u+v;
189 GET_FLOAT_WORD(is,p_h);
190 SET_FLOAT_WORD(p_h,is&0xfffff000);
191 p_l = v-(p_h-u);
192 z_h = cp_h*p_h; /* cp_h+cp_l = 2/(3*log2) */
193 z_l = cp_l*p_h+p_l*cp+dp_l[k];
194 /* log2(ax) = (s+..)*2/(3*log2) = n + dp_h + z_h + z_l */
195 t = (float)n;
196 t1 = (((z_h+z_l)+dp_h[k])+t);
197 GET_FLOAT_WORD(is,t1);
198 SET_FLOAT_WORD(t1,is&0xfffff000);
199 t2 = z_l-(((t1-t)-dp_h[k])-z_h);
200 }
201
202 /* split up y into y1+y2 and compute (y1+y2)*(t1+t2) */
203 GET_FLOAT_WORD(is,y);
204 SET_FLOAT_WORD(y1,is&0xfffff000);
205 p_l = (y-y1)*t1+y*t2;
206 p_h = y1*t1;
207 z = p_l+p_h;
208 GET_FLOAT_WORD(j,z);
209 if (j>0x43000000) /* if z > 128 */
210 return sn*huge*huge; /* overflow */
211 else if (j==0x43000000) { /* if z == 128 */
212 if(p_l+ovt>z-p_h) return sn*huge*huge; /* overflow */
213 }
214 else if ((j&0x7fffffff)>0x43160000) /* z <= -150 */
215 return sn*tiny*tiny; /* underflow */
216 else if (j==0xc3160000){ /* z == -150 */
217 if(p_l<=z-p_h) return sn*tiny*tiny; /* underflow */
218 }
219 /*
220 * compute 2**(p_h+p_l)
221 */
222 i = j&0x7fffffff;
223 k = (i>>23)-0x7f;
224 n = 0;
225 if(i>0x3f000000) { /* if |z| > 0.5, set n = [z+0.5] */
226 n = j+(0x00800000>>(k+1));
227 k = ((n&0x7fffffff)>>23)-0x7f; /* new k for n */
228 SET_FLOAT_WORD(t,n&~(0x007fffff>>k));
229 n = ((n&0x007fffff)|0x00800000)>>(23-k);
230 if(j<0) n = -n;
231 p_h -= t;
232 }
233 t = p_l+p_h;
234 GET_FLOAT_WORD(is,t);
235 SET_FLOAT_WORD(t,is&0xffff8000);
236 u = t*lg2_h;
237 v = (p_l-(t-p_h))*lg2+t*lg2_l;
238 z = u+v;
239 w = v-(z-u);
240 t = z*z;
241 t1 = z - t*(P1+t*(P2+t*(P3+t*(P4+t*P5))));
242 r = (z*t1)/(t1-two)-(w+z*w);
243 z = one-(r-z);
244 GET_FLOAT_WORD(j,z);
245 j += (n<<23);
246 if((j>>23)<=0) z = scalbnf(z,n); /* subnormal output */
247 else SET_FLOAT_WORD(z,j);
248 return sn*z;
249 }
250