1 /*
2 * ====================================================
3 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
4 *
5 * Developed at SunPro, a Sun Microsystems, Inc. business.
6 * Permission to use, copy, modify, and distribute this
7 * software is freely granted, provided that this notice
8 * is preserved.
9 * ====================================================
10 */
11
12 #include <sys/cdefs.h>
13 __FBSDID("$FreeBSD$");
14
15 /*
16 * Float version of k_log.h. See the latter for most comments.
17 */
18
19 static const float
20 /* |(log(1+s)-log(1-s))/s - Lg(s)| < 2**-34.24 (~[-4.95e-11, 4.97e-11]). */
21 Lg1 = 0xaaaaaa.0p-24, /* 0.66666662693 */
22 Lg2 = 0xccce13.0p-25, /* 0.40000972152 */
23 Lg3 = 0x91e9ee.0p-25, /* 0.28498786688 */
24 Lg4 = 0xf89e26.0p-26; /* 0.24279078841 */
25
26 static inline float
k_log1pf(float f)27 k_log1pf(float f)
28 {
29 float hfsq,s,z,R,w,t1,t2;
30
31 s = f/((float)2.0+f);
32 z = s*s;
33 w = z*z;
34 t1= w*(Lg2+w*Lg4);
35 t2= z*(Lg1+w*Lg3);
36 R = t2+t1;
37 hfsq=(float)0.5*f*f;
38 return s*(hfsq+R);
39 }
40