sheets/doc/NOTES.high-precision

0001 Number class
0002 ============
0003
0004 Requirements
0005 ------------
0006 - Should increase the numerical precision.
0007 - Should fallback to (long) double and use its operators directly,
0008   so that the code could be optimized by the compiler.
0009 - High precision support should be either:
0010     - a run-time option by using plugins (preferred)
0011     - a compile-time option
0012
0013 Options
0014 -------
0015 - static polymorphism: CRTP
0016 - dynamic polymorphism: interface is a usual class with pure virtual methods;
0017   Q_DECLARE_INTERFACE, Q_INTERFACES can be used here
0018 - QVariant/QMetaType allows to create objects dynamically on run-time:
0019     - double can be used directly
0020     - custom types actually too, but dynamic polymorphism needs pointers
0021     - QMetaType::construct() returns void*
0022 - using QVariant in the calculation methods to carry the number and create
0023   a double or the custom type at run-time is possible
0024
0025 Advantages/Drawbacks/Conclusion
0026 -------------------------------
0027 - CRTP allows to inline the methods and using (long) double's operators becomes
0028   possible
0029 - using virtuals does not allow to inline the methods, if pointer or references
0030   to the object are used, which is necessary in the case of dynamic binding
0031 - inlining operators does not work with dynamic polymorphism
0032 - having high-precision and the (long) double fallback needs a common base
0033
0034 Impossible solution(s)
0035 ----------------------
0036 1.
0037 - derive the type using (long) double type from a base using CRTP approach
0038 - derive the interface for the dynamic binding also from this base
0039 - derive concrete implementations from the interface
0040 Reason:
0041 - inserting a dynamically created type as template parameter into the CRTP base
0042   is not possible
0043 2.
0044 - use QVariant as data carrier/common base
0045 - mirror QVariant's behaviour in KSpread::Value
0046 Reason:
0047 - the QVariant::Type does not suffice, you need to know the type in order to use
0048   it
0049
0050 Possible solution(s)
0051 --------------------
0052 0.
0053 - the information, which type is in use, that's a QVariant::Type, should be
0054   stored per document, more precisely in CalculationSettings
0055
0056
0057 union
0058 {
0059 double a;
0060 void* b;
0061 };