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[/] [openrisc/] [trunk/] [gnu-src/] [newlib-1.17.0/] [newlib/] [libm/] [math/] [ef_log.c] - Rev 193
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/* ef_log.c -- float version of e_log.c. * Conversion to float by Ian Lance Taylor, Cygnus Support, ian@cygnus.com. */ /* * ==================================================== * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved. * * Developed at SunPro, a Sun Microsystems, Inc. business. * Permission to use, copy, modify, and distribute this * software is freely granted, provided that this notice * is preserved. * ==================================================== */ #include "fdlibm.h" #ifdef __STDC__ static const float #else static float #endif ln2_hi = 6.9313812256e-01, /* 0x3f317180 */ ln2_lo = 9.0580006145e-06, /* 0x3717f7d1 */ two25 = 3.355443200e+07, /* 0x4c000000 */ Lg1 = 6.6666668653e-01, /* 3F2AAAAB */ Lg2 = 4.0000000596e-01, /* 3ECCCCCD */ Lg3 = 2.8571429849e-01, /* 3E924925 */ Lg4 = 2.2222198546e-01, /* 3E638E29 */ Lg5 = 1.8183572590e-01, /* 3E3A3325 */ Lg6 = 1.5313838422e-01, /* 3E1CD04F */ Lg7 = 1.4798198640e-01; /* 3E178897 */ #ifdef __STDC__ static const float zero = 0.0; #else static float zero = 0.0; #endif #ifdef __STDC__ float __ieee754_logf(float x) #else float __ieee754_logf(x) float x; #endif { float hfsq,f,s,z,R,w,t1,t2,dk; __int32_t k,ix,i,j; GET_FLOAT_WORD(ix,x); k=0; if (FLT_UWORD_IS_ZERO(ix&0x7fffffff)) return -two25/zero; /* log(+-0)=-inf */ if (ix<0) return (x-x)/zero; /* log(-#) = NaN */ if (!FLT_UWORD_IS_FINITE(ix)) return x+x; if (FLT_UWORD_IS_SUBNORMAL(ix)) { k -= 25; x *= two25; /* subnormal number, scale up x */ GET_FLOAT_WORD(ix,x); } k += (ix>>23)-127; ix &= 0x007fffff; i = (ix+(0x95f64<<3))&0x800000; SET_FLOAT_WORD(x,ix|(i^0x3f800000)); /* normalize x or x/2 */ k += (i>>23); f = x-(float)1.0; if((0x007fffff&(15+ix))<16) { /* |f| < 2**-20 */ if(f==zero) { if(k==0) return zero; else {dk=(float)k; return dk*ln2_hi+dk*ln2_lo;}} R = f*f*((float)0.5-(float)0.33333333333333333*f); if(k==0) return f-R; else {dk=(float)k; return dk*ln2_hi-((R-dk*ln2_lo)-f);} } s = f/((float)2.0+f); dk = (float)k; z = s*s; i = ix-(0x6147a<<3); w = z*z; j = (0x6b851<<3)-ix; t1= w*(Lg2+w*(Lg4+w*Lg6)); t2= z*(Lg1+w*(Lg3+w*(Lg5+w*Lg7))); i |= j; R = t2+t1; if(i>0) { hfsq=(float)0.5*f*f; if(k==0) return f-(hfsq-s*(hfsq+R)); else return dk*ln2_hi-((hfsq-(s*(hfsq+R)+dk*ln2_lo))-f); } else { if(k==0) return f-s*(f-R); else return dk*ln2_hi-((s*(f-R)-dk*ln2_lo)-f); } }
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