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
k_log1pf(float f)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