1 /* e_logf.c -- float version of e_log.c. 2 * Conversion to float by Ian Lance Taylor, Cygnus Support, ian@cygnus.com. 3 */ 4 5 /* 6 * ==================================================== 7 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved. 8 * 9 * Developed at SunPro, a Sun Microsystems, Inc. business. 10 * Permission to use, copy, modify, and distribute this 11 * software is freely granted, provided that this notice 12 * is preserved. 13 * ==================================================== 14 */ 15 16 #include <sys/cdefs.h> 17 #if defined(LIBM_SCCS) && !defined(lint) 18 __RCSID("$NetBSD: e_log2f.c,v 1.1 2005/07/21 12:55:58 christos Exp $"); 19 #endif 20 21 #include "math.h" 22 #include "math_private.h" 23 24 static const float 25 ln2 = 0.6931471805599452862268, 26 two25 = 3.355443200e+07, /* 0x4c000000 */ 27 Lg1 = 6.6666668653e-01, /* 3F2AAAAB */ 28 Lg2 = 4.0000000596e-01, /* 3ECCCCCD */ 29 Lg3 = 2.8571429849e-01, /* 3E924925 */ 30 Lg4 = 2.2222198546e-01, /* 3E638E29 */ 31 Lg5 = 1.8183572590e-01, /* 3E3A3325 */ 32 Lg6 = 1.5313838422e-01, /* 3E1CD04F */ 33 Lg7 = 1.4798198640e-01; /* 3E178897 */ 34 35 static const float zero = 0.0; 36 37 float 38 __ieee754_log2f(float x) 39 { 40 float hfsq,f,s,z,R,w,t1,t2,dk; 41 int32_t k,ix,i,j; 42 43 GET_FLOAT_WORD(ix,x); 44 45 k=0; 46 if (ix < 0x00800000) { /* x < 2**-126 */ 47 if ((ix&0x7fffffff)==0) 48 return -two25/zero; /* log(+-0)=-inf */ 49 if (ix<0) return (x-x)/zero; /* log(-#) = NaN */ 50 k -= 25; x *= two25; /* subnormal number, scale up x */ 51 GET_FLOAT_WORD(ix,x); 52 } 53 if (ix >= 0x7f800000) return x+x; 54 k += (ix>>23)-127; 55 ix &= 0x007fffff; 56 i = (ix+(0x95f64<<3))&0x800000; 57 SET_FLOAT_WORD(x,ix|(i^0x3f800000)); /* normalize x or x/2 */ 58 k += (i>>23); 59 dk = (float)k; 60 f = x-(float)1.0; 61 if((0x007fffff&(15+ix))<16) { /* |f| < 2**-20 */ 62 if (f==zero) 63 return (dk); 64 R = f*f*((float)0.5-(float)0.33333333333333333*f); 65 return (dk-(R-f)/ln2); 66 } 67 s = f/((float)2.0+f); 68 z = s*s; 69 i = ix-(0x6147a<<3); 70 w = z*z; 71 j = (0x6b851<<3)-ix; 72 t1= w*(Lg2+w*(Lg4+w*Lg6)); 73 t2= z*(Lg1+w*(Lg3+w*(Lg5+w*Lg7))); 74 i |= j; 75 R = t2+t1; 76 if(i>0) { 77 hfsq=(float)0.5*f*f; 78 return (dk-(hfsq-s*(hfsq+R)-f)/ln2); 79 } else 80 return (dk-((s*(f-R))-f)/ln2); 81 } 82