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