xref: /freebsd/lib/msun/src/k_logf.h (revision 1edb7116)
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 /*
13  * Float version of k_log.h.  See the latter for most comments.
14  */
15 
16 static const float
17 /* |(log(1+s)-log(1-s))/s - Lg(s)| < 2**-34.24 (~[-4.95e-11, 4.97e-11]). */
18 Lg1 =      0xaaaaaa.0p-24,	/* 0.66666662693 */
19 Lg2 =      0xccce13.0p-25,	/* 0.40000972152 */
20 Lg3 =      0x91e9ee.0p-25,	/* 0.28498786688 */
21 Lg4 =      0xf89e26.0p-26;	/* 0.24279078841 */
22 
23 static inline float
24 k_log1pf(float f)
25 {
26 	float hfsq,s,z,R,w,t1,t2;
27 
28  	s = f/((float)2.0+f);
29 	z = s*s;
30 	w = z*z;
31 	t1= w*(Lg2+w*Lg4);
32 	t2= z*(Lg1+w*Lg3);
33 	R = t2+t1;
34 	hfsq=(float)0.5*f*f;
35 	return s*(hfsq+R);
36 }
37