1 /* e_logf.c -- float version of e_log.c. 2 * Conversion to float by Ian Lance Taylor, Cygnus Support, ian (at) 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 #ifndef lint 17 static char rcsid[] = "$FreeBSD: src/lib/msun/src/e_logf.c,v 1.8 2005/11/12 18:20:09 bde Exp $"; 18 #endif 19 20 #include "math.h" 21 #include "math_private.h" 22 23 static const float 24 ln2_hi = 6.9313812256e-01, /* 0x3f317180 */ 25 ln2_lo = 9.0580006145e-06, /* 0x3717f7d1 */ 26 two25 = 3.355443200e+07, /* 0x4c000000 */ 27 /* |(log(1+s)-log(1-s))/s - Lg(s)| < 2**-34.24 (~[-4.95e-11, 4.97e-11]). */ 28 Lg1 = 0xaaaaaa.0p-24, /* 0.66666662693 */ 29 Lg2 = 0xccce13.0p-25, /* 0.40000972152 */ 30 Lg3 = 0x91e9ee.0p-25, /* 0.28498786688 */ 31 Lg4 = 0xf89e26.0p-26; /* 0.24279078841 */ 32 33 static const float zero = 0.0; 34 35 float 36 __ieee754_logf(float x) 37 { 38 float hfsq,f,s,z,R,w,t1,t2,dk; 39 int32_t k,ix,i,j; 40 41 GET_FLOAT_WORD(ix,x); 42 43 k=0; 44 if (ix < 0x00800000) { /* x < 2**-126 */ 45 if ((ix&0x7fffffff)==0) 46 return -two25/zero; /* log(+-0)=-inf */ 47 if (ix<0) return (x-x)/zero; /* log(-#) = NaN */ 48 k -= 25; x *= two25; /* subnormal number, scale up x */ 49 GET_FLOAT_WORD(ix,x); 50 } 51 if (ix >= 0x7f800000) return x+x; 52 k += (ix>>23)-127; 53 ix &= 0x007fffff; 54 i = (ix+(0x95f64<<3))&0x800000; 55 SET_FLOAT_WORD(x,ix|(i^0x3f800000)); /* normalize x or x/2 */ 56 k += (i>>23); 57 f = x-(float)1.0; 58 if((0x007fffff&(15+ix))<16) { /* |f| < 2**-20 */ 59 if(f==zero) if(k==0) return zero; else {dk=(float)k; 60 return dk*ln2_hi+dk*ln2_lo;} 61 R = f*f*((float)0.5-(float)0.33333333333333333*f); 62 if(k==0) return f-R; else {dk=(float)k; 63 return dk*ln2_hi-((R-dk*ln2_lo)-f);} 64 } 65 s = f/((float)2.0+f); 66 dk = (float)k; 67 z = s*s; 68 i = ix-(0x6147a<<3); 69 w = z*z; 70 j = (0x6b851<<3)-ix; 71 t1= w*(Lg2+w*Lg4); 72 t2= z*(Lg1+w*Lg3); 73 i |= j; 74 R = t2+t1; 75 if(i>0) { 76 hfsq=(float)0.5*f*f; 77 if(k==0) return f-(hfsq-s*(hfsq+R)); else 78 return dk*ln2_hi-((hfsq-(s*(hfsq+R)+dk*ln2_lo))-f); 79 } else { 80 if(k==0) return f-s*(f-R); else 81 return dk*ln2_hi-((s*(f-R)-dk*ln2_lo)-f); 82 } 83 } 84
