author | Dremov Kirill (Nokia-D-MSW/Tampere) <kirill.dremov@nokia.com> |
Fri, 11 Jun 2010 15:26:22 +0300 | |
changeset 34 | 5fae379060a7 |
parent 0 | e4d67989cc36 |
permissions | -rw-r--r-- |
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/*-------------------------------------------------------------------- |
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*© Portions copyright (c) 2006 Nokia Corporation. All rights reserved. |
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*-------------------------------------------------------------------- |
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*/ |
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/* @(#)e_log10.c 1.3 95/01/18 */ |
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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 SunSoft, 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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#ifndef __SYMBIAN32__ |
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#ifndef lint |
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static char rcsid[] = "$FreeBSD: src/lib/msun/src/e_log10.c,v 1.11 2005/02/04 18:26:06 das Exp $"; |
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#endif |
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#endif //__SYMBIAN32__ |
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|
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/* __ieee754_log10(x) |
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* Return the base 10 logarithm of x |
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* |
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* Method : |
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* Let log10_2hi = leading 40 bits of log10(2) and |
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* log10_2lo = log10(2) - log10_2hi, |
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* ivln10 = 1/log(10) rounded. |
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* Then |
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* n = ilogb(x), |
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* if(n<0) n = n+1; |
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* x = scalbn(x,-n); |
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* log10(x) := n*log10_2hi + (n*log10_2lo + ivln10*log(x)) |
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* |
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* Note 1: |
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* To guarantee log10(10**n)=n, where 10**n is normal, the rounding |
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* mode must set to Round-to-Nearest. |
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* Note 2: |
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* [1/log(10)] rounded to 53 bits has error .198 ulps; |
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* log10 is monotonic at all binary break points. |
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* |
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* Special cases: |
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* log10(x) is NaN with signal if x < 0; |
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* log10(+INF) is +INF with no signal; log10(0) is -INF with signal; |
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* log10(NaN) is that NaN with no signal; |
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* log10(10**N) = N for N=0,1,...,22. |
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* |
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* Constants: |
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* The hexadecimal values are the intended ones for the following constants. |
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* The decimal values may be used, provided that the compiler will convert |
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* from decimal to binary accurately enough to produce the hexadecimal values |
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* shown. |
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*/ |
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|
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#include <math.h> |
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#include "math_private.h" |
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|
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static const double |
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two54 = 1.80143985094819840000e+16, /* 0x43500000, 0x00000000 */ |
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ivln10 = 4.34294481903251816668e-01, /* 0x3FDBCB7B, 0x1526E50E */ |
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log10_2hi = 3.01029995663611771306e-01, /* 0x3FD34413, 0x509F6000 */ |
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log10_2lo = 3.69423907715893078616e-13; /* 0x3D59FEF3, 0x11F12B36 */ |
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|
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#ifdef __SYMBIAN32__ |
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static const double zero = 0; |
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#else//__SYMBIAN32__ |
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static const double zero = 0.0; |
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#endif//__SYMBIAN32__ |
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|
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EXPORT_C double __ieee754_log10(double x) |
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{ |
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double y,z; |
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int32_t i,k,hx; |
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u_int32_t lx; |
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EXTRACT_WORDS(hx,lx,x); |
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k=0; |
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if (hx < 0x00100000) { /* x < 2**-1022 */ |
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if (((hx&0x7fffffff)|lx)==0) |
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return -two54/zero; /* log(+-0)=-inf */ |
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if (hx<0) return (x-x)/zero; /* log(-#) = NaN */ |
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|
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k -= 54; x *= two54; /* subnormal number, scale up x */ |
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GET_HIGH_WORD(hx,x); |
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} |
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if (hx >= 0x7ff00000) return x+x; |
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k += (hx>>20)-1023; |
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i = ((u_int32_t)k&0x80000000)>>31; |
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hx = (hx&0x000fffff)|((0x3ff-i)<<20); |
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y = (double)(k+i); |
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SET_HIGH_WORD(x,hx); |
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z = y*log10_2lo + ivln10*__ieee754_log(x); |
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return z+y*log10_2hi; |
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} |