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 __kernel_log(x). See k_log.c for details. 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 __kernel_logf(float x) 28 { 29 float hfsq,f,s,z,R,w,t1,t2; 30 int32_t ix,i,j; 31 32 GET_FLOAT_WORD(ix,x); 33 34 f = x-(float)1.0; 35 if((0x007fffff&(0x8000+ix))<0xc000) { /* -2**-9 <= f < 2**-9 */ 36 if(f==0.0f) return 0.0f; 37 return f*f*((float)0.33333333333333333*f-(float)0.5); 38 } 39 s = f/((float)2.0+f); 40 z = s*s; 41 ix &= 0x007fffff; 42 i = ix-(0x6147a<<3); 43 w = z*z; 44 j = (0x6b851<<3)-ix; 45 t1= w*(Lg2+w*Lg4); 46 t2= z*(Lg1+w*Lg3); 47 i |= j; 48 R = t2+t1; 49 if(i>0) { 50 hfsq=(float)0.5*f*f; 51 return s*(hfsq+R) - hfsq; 52 } else { 53 return s*(R-f); 54 } 55 } 56