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C++ Double - 8th point decimals
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Hi,
I have a problem that happens very rarely. I have a calculation which ads (for example) -15000.00 to 15575.51 and saves the results to an oracle database. However, the reslut in the databse is 575.51000002
Both figures are loaded elsewhere from the database and either have 0 or 2 decimals as in the example above.
The code processes millions of transactions, but less than .01 % has this error. Any ideas?
Thanks,
Shawn
I have a problem that happens very rarely. I have a calculation which ads (for example) -15000.00 to 15575.51 and saves the results to an oracle database. However, the reslut in the databse is 575.51000002
Both figures are loaded elsewhere from the database and either have 0 or 2 decimals as in the example above.
The code processes millions of transactions, but less than .01 % has this error. Any ideas?
Thanks,
Shawn
AddUpInputAK( int iIndexInputAK, int iAccumPos, int iAccumNeg, double* naSumsBW, double* naSumsRW ) {int iRet = SQC_C_Success; int iIndexSum; double nBetragBook; double nBetragBest; double nBetragKto; double nBetragRef; int iAK_Vorz; //// // //// if ( ALG_IsIntNull( iIndexInputAK ) ) {goto L_Eof;} if ( ALG_IsIntNull( iAccumPos ) && ALG_IsIntNull( iAccumNeg ) ) {goto L_Eof;} iIndexSum = 0; nBetragBook = m_naInpAbrKompBetrag[iIndexInputAK]; if ( ALG_IsDoubleNull( nBetragBook ) ) {goto L_Eof;} //// // Correct signage //// iAK_Vorz = 1; if ( m_saInpAbrKompVorz[iIndexInputAK].Left( 1 ) == "-" ) {iAK_Vorz = -1; nBetragBook = nBetragBook * ( -1.0);} if ( m_sPosArt == "KTO" ) { //// // Accounts //// if ( m_sKtoWhg == m_saInpAbrKompWhg[iIndexInputAK] ) {nBetragKto = m_naInpAbrKompBetrag[iIndexInputAK];if ( iAK_Vorz < 0 ) {nBetragKto = nBetragKto * ( -1 );} else {nBetragKto = nBetragBook;} ALG_SetDoubleNull( &nBetragKto ); } if ( ! ALG_IsDoubleNull( nBetragKto ) ) {naSumsBW[iIndexSum] = naSumsBW[iIndexSum] + nBetragKto;} } L_Eof: return( iRet ); }
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Join Date: May 2006
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I'd guess that it's due to how floating point values are stored imprecisely in memory, causing the weird results to come up on rare occasions.
>The code processes millions of transactions, but less than .01 % has this error. Any ideas?
That's a typical floating-point rounding fudge. If it's a serious enough problem, you can try to use a more precise type such as long double, or remove floating-point altogether to maintain exact precision. Though I suspect that an imprecision at the eighth decimal place isn't that much of an issue unless you're trying to do something with vanilla C++ types that shouldn't be done with vanilla C++ types. If that's the case, you really need to get a high precision mathematics library.
That's a typical floating-point rounding fudge. If it's a serious enough problem, you can try to use a more precise type such as long double, or remove floating-point altogether to maintain exact precision. Though I suspect that an imprecision at the eighth decimal place isn't that much of an issue unless you're trying to do something with vanilla C++ types that shouldn't be done with vanilla C++ types. If that's the case, you really need to get a high precision mathematics library.
I'm here to prove you wrong.
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