compiler/stdc/math/k_logf.h

   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 #ifndef lint
  13 static char rcsid[] = "$FreeBSD: src/lib/msun/src/k_logf.h,v 1.3 2011/10/15 05:23:28 das Exp $");
  14 #endif
  15
  16 /*
  17  * Float version of k_log.h.  See the latter for most comments.
  18  */
  19
  20 static const float
  21 /* |(log(1+s)-log(1-s))/s - Lg(s)| < 2**-34.24 (~[-4.95e-11, 4.97e-11]). */
  22 Lg1 =      0xaaaaaa.0p-24,      /* 0.66666662693 */
  23 Lg2 =      0xccce13.0p-25,      /* 0.40000972152 */
  24 Lg3 =      0x91e9ee.0p-25,      /* 0.28498786688 */
  25 Lg4 =      0xf89e26.0p-26;      /* 0.24279078841 */
  26
  27 static inline float
  28 k_log1pf(float f)
  29 {
  30         float hfsq,s,z,R,w,t1,t2;
  31
  32         s = f/((float)2.0+f);
  33         z = s*s;
  34         w = z*z;
  35         t1= w*(Lg2+w*Lg4);
  36         t2= z*(Lg1+w*Lg3);
  37         R = t2+t1;
  38         hfsq=(float)0.5*f*f;
  39         return s*(hfsq+R);
  40 }