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