ba237a9d91
Files correlati : Ricompilazione Demo : [ ] Commento : Aggiunti i sorgenti per Greenleaf Math Library (gfm.dll) git-svn-id: svn://10.65.10.50/trunk@10079 c028cbd2-c16b-5b4b-a496-9718f37d4682
67 lines
1.3 KiB
C
Executable File
67 lines
1.3 KiB
C
Executable File
/* DEC *Log10Decimal(pDst,pSrc)
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* ARGUMENT
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* pDst is a DEC pointer to the destination.
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* pSrc is a DEC pointer to the source.
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*
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* DESCRIPTION
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* Takes the base 10 logarithm of pSrc, storing result in pDst.
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*
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* SIDE EFFECTS
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* None.
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*
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* RETURNS
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* pDst if successful, GM_NULL otherwise.
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*
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* ALGORTIHM
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* log x = (1/ln10) * ln(x), with ln(x) calculated as:
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*
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* pSrc = 10^m * 2^(-d) * x .7 <= x < 1.4
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* z = (x - 1) / (x + 1)
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* ln pSrc = m * ln 10 - d * ln 2 + ln x
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* ln x = 2 * SUM [z^(2 * n + 1) / (2 * n + 1)]
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* n = 0, 1, 2, 3,...
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*
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* POSSIBLE ERROR CODES
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*
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* GM_NULLPOINTER
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* GM_IMAG
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*
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* AUTHOR
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* Jared Levy 4 / 8 / 1987
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* Copyright (C) 1987-1990 Greenleaf Software Inc. All rights reserved.
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*
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* MODIFICATIONS
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*
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*
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*/
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#include <stdio.h>
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#include "gm.h"
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#include "gmsystem.h"
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DEC *Log10Decimal(pDst,pSrc)
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DEC *pDst;
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DEC *pSrc;
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{
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DEC dtemp, *temp=&dtemp;
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_MacStart(GM_DLOG);
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_MacInVarD(pSrc);
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_MacOutVarD(pDst);
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if (!_MacIsDecP(pSrc)) {
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_MacErr(GM_IMAG);
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_MacRet(GM_NULL);
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}
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_MacDZero(temp);
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/* first take ln(pSrc) */
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(void) _LnDec80Bit(temp, pSrc); /* can't fail if pSrc is positive */
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/* then (1/ln(10))* ln(pSrc) */
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(void) _MulDec80Bit(pDst, &decReciprocalOfLn10, temp);
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/* then back to 64-bit */
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(void) _Sq5UnsTo4Uns(pDst); /* cannot be unsuccessful */
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_MacRet(pDst);
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}
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