k_logf.h (996B)
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 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 }