[GNC] gnucash_user: rounding errors and significant digits

[Bruce McCoy]

Jim,

 

Whatare some of the options available to GnuCash programmers today toimprove precision? Here is one group.




Decimal-FloatingArithmetic 

GeneralDecimal Arithmetic 

 http://speleotrove.com/decimal 

 http://speleotrove.com/decimal/#decNumber

 http://speleotrove.com/decimal/#links

 http://speleotrove.com/decimal/#implement

ThedecNumber Library Version 3.68 

 https://speleotrove.com/decimal/decnumber.html

decimal— Decimal fixed point and floating point arithmetic 

 https://speleotrove.com/decimal/decarith.html



C++libraries Decimal-Arithmetic

GMP 

 https://gmplib.org/

GNUMPFR Library 

 https://www.mpfr.org/

 https://www.mpfr.org/ports.html

 https://github.com/microsoft/vcpkg.git (Windows)

mpdecimal

 https://www.bytereef.org/mpdecimal/




Java

ClassBigInteger 

 https://docs.oracle.com/javase/8/docs/api/java/math/BigInteger.html

Usesof Class java.math.BigDecimal 

 https://docs.oracle.com/javase/8/docs/api/java/math/class-use/BigDecimal.html




Python Decimal-Arithmetic

15.Floating Point Arithmetic: Issues and Limitations  python

 https://docs.python.org/3/tutorial/floatingpoint.html

cdecimal- Python module (2.7 – 3.2) 

 https://www.bytereef.org/mpdecimal/doc/cdecimal/index.html




DecimalArithmetic Functions 

 https://learn.microsoft.com/en-us/previous-versions/windows/desktop/automat/decimal-arithmetic-functions?redirectedfrom=MSDN




Listof arbitrary-precision arithmetic software 

 https://en.wikipedia.org/wiki/List_of_arbitrary-precision_arithmetic_software




IEEE754-2008 revision 

 IEEE 754-2008 revision - Wikipedia


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IEEE 754-2008 revision - Wikipedia

IEEE 754-2008 (previously known as IEEE 754r) is a revision of the IEEE 754 standard for floating-point arithmet...
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Justto name two that probably everyone in this area knows, the GNUMultiple Precision Arithmetic Library version 6.3.0 and the MPFRMultiple Precision Floating Point Reliable Library were released in2023. I have no idea which of all these resources would be preferredby the understaffed and overworked GnuCash programmers.

 

Whatcan we do while awaiting a, say, decimal arithmetic or arbitraryprecision arithmetic software or some other excellent solution? Ifthe GnuCash community would like to have Gnucash software match thestatements from the investment firms calculating their holdings orthe members' own records, we could consider making a suggestion whichwould be relatively easy to code. 

 

Currently,given the cost of the transaction and the number of shares traded,GnuCash calculates the price per share. On occasion, the Gnucashcalculation results are unexpected. In our example at hand, you find"Logically, $value = $price/share * #shares, and this should beprecise equality. But is possible for a brokerage statement to reportvalues which do not have precise equality. It sounds like FederatedHermes reported $15.00 = $6.26 * 2.396, but the actual $value of this$price and #shares is $14.99896, a difference of $0.00104."

 

Inthis example, if we could allow the user to enter $15.00, we wouldhave a solution, albeit a manual one.




GnuCashcalculates $value = $price/share * #shares. A screen showing thosethree results in data-entry fields instead of read-only fields wouldallow the user to change the aberrant result, which could be saved. The computer could be instructed to not re-calculate these threevalues again, until, say, the user changed one of them to null orzero. Such a process is relatively simple to program. It wouldserve the purpose until a perfect solution was developed.

 

Isthe GnuCash community be interested in having the values in GnuCashand the brokerage statements be identical? 

Ifyou are a member of the GnuCash community, here is an invitation toexpress yourself concerning this topic. Feel free to comment




BestRegards,

Bruce









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