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[/] [or1k/] [trunk/] [newlib-1.10.0/] [newlib/] [libm/] [math/] [ef_log.c] - Blame information for rev 1773

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1 1010 ivang
/* ef_log.c -- float version of e_log.c.
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 * Conversion to float by Ian Lance Taylor, Cygnus Support, ian@cygnus.com.
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 */
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/*
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 * ====================================================
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 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
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 *
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 * Developed at SunPro, a Sun Microsystems, Inc. business.
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 * Permission to use, copy, modify, and distribute this
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 * software is freely granted, provided that this notice
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 * is preserved.
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 * ====================================================
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 */
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#include "fdlibm.h"
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#ifdef __STDC__
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static const float
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#else
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static float
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#endif
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ln2_hi =   6.9313812256e-01,    /* 0x3f317180 */
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ln2_lo =   9.0580006145e-06,    /* 0x3717f7d1 */
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two25 =    3.355443200e+07,     /* 0x4c000000 */
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Lg1 = 6.6666668653e-01, /* 3F2AAAAB */
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Lg2 = 4.0000000596e-01, /* 3ECCCCCD */
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Lg3 = 2.8571429849e-01, /* 3E924925 */
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Lg4 = 2.2222198546e-01, /* 3E638E29 */
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Lg5 = 1.8183572590e-01, /* 3E3A3325 */
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Lg6 = 1.5313838422e-01, /* 3E1CD04F */
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Lg7 = 1.4798198640e-01; /* 3E178897 */
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#ifdef __STDC__
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static const float zero   =  0.0;
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#else
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static float zero   =  0.0;
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#endif
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#ifdef __STDC__
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        float __ieee754_logf(float x)
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#else
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        float __ieee754_logf(x)
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        float x;
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#endif
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{
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        float hfsq,f,s,z,R,w,t1,t2,dk;
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        __int32_t k,ix,i,j;
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        GET_FLOAT_WORD(ix,x);
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        k=0;
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        if (FLT_UWORD_IS_ZERO(ix&0x7fffffff))
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            return -two25/zero;         /* log(+-0)=-inf */
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        if (ix<0) return (x-x)/zero;     /* log(-#) = NaN */
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        if (!FLT_UWORD_IS_FINITE(ix)) return x+x;
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        if (FLT_UWORD_IS_SUBNORMAL(ix)) {
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            k -= 25; x *= two25; /* subnormal number, scale up x */
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            GET_FLOAT_WORD(ix,x);
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        }
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        k += (ix>>23)-127;
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        ix &= 0x007fffff;
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        i = (ix+(0x95f64<<3))&0x800000;
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        SET_FLOAT_WORD(x,ix|(i^0x3f800000));    /* normalize x or x/2 */
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        k += (i>>23);
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        f = x-(float)1.0;
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        if((0x007fffff&(15+ix))<16) {   /* |f| < 2**-20 */
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           if(f==zero) { if(k==0) return zero;  else {dk=(float)k;
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                                return dk*ln2_hi+dk*ln2_lo;}}
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            R = f*f*((float)0.5-(float)0.33333333333333333*f);
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            if(k==0) return f-R; else {dk=(float)k;
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                     return dk*ln2_hi-((R-dk*ln2_lo)-f);}
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        }
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        s = f/((float)2.0+f);
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        dk = (float)k;
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        z = s*s;
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        i = ix-(0x6147a<<3);
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        w = z*z;
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        j = (0x6b851<<3)-ix;
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        t1= w*(Lg2+w*(Lg4+w*Lg6));
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        t2= z*(Lg1+w*(Lg3+w*(Lg5+w*Lg7)));
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        i |= j;
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        R = t2+t1;
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        if(i>0) {
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            hfsq=(float)0.5*f*f;
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            if(k==0) return f-(hfsq-s*(hfsq+R)); else
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                     return dk*ln2_hi-((hfsq-(s*(hfsq+R)+dk*ln2_lo))-f);
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        } else {
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            if(k==0) return f-s*(f-R); else
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                     return dk*ln2_hi-((s*(f-R)-dk*ln2_lo)-f);
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        }
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}

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