Eric, On Friday 05 October 2012 13:48:20 you wrote:
> Hi Thomas: > > Actually that was the function that I was looking at and referring to. I > tried looking at it but I'll be honest, I am struggling trying to figure > out just what exactly it is doing. > > I see it takes in a String value currency, which I am assuming is the > constant defined somewhere for the currency denomination the user is using, > then it integer for precision and a boolean to for thousands. So I got all > that down. :) > > I am guessing that you are controlling the precision of > accounts/transactions past two for things like stock prices and > transactions right? So since I am not implementing this type I can safely > "ignore" that, but need to keep it in the back of my mind for future > reference. Don't forget those currencies that are denominated in 1/1000 (some currencies used in the middle east are using that). Also, we know of currencies that don't have a fraction (the Hungarian Forint comes to mind). > > It looks like the meat of the actual function starts with the on line 145: > #if 1 > > and runs through line 161: > mpz_class right = (valueRef() - mpq_class(left)) * denom; > > I am lost looking at this stuff, the rest of the function looks like it is > just string manipulation which is easy enough to replicate. :) It took me a while to write it as well ;) > > What is a mpz_class? What is actually going on with lines 152, 154, 160 and > 161? Check http://gmplib.org/manual/C_002b_002b-Interface- Integers.html#C_002b_002b-Interface-Integers for information about the mpz_class. It is basically an integer with arbitrary precision. mpq_class is a rational which can be thought of as two mpz_class members (nominator and denominator). Information for mpq can be found here: http://gmplib.org/manual/C_002b_002b-Interface-Rationals.html#C_002b_002b- Interface-Rationals. AlkValue (and thus MyMoneyMoney) simply wrap the mpq_class value with a nice interface) and a bit of logic not found in libgmp. 'left' in the logic takes the part left of the decimal symbol, 'right' the part to the right (fraction). Looking at value = static_cast<MyMoneyMoney>(convertDenominator(d)).valueRef().get_num(); For convertDenominator we find in alkvalue.h: /** * Returns the current value converted to the given @a denom (default is 100 * or two digits of precision). The rounding method used is controlled by * the @a how argument and defaults to @p RoundRound. */ AlkValue convertDenominator(const int denom = 100, const RoundingMethod how = RoundRound) const; The 'current value' is the value of the current object (not the variable 'value' in the above assignment statement. The logic of this method is a bit tricky. Check the source in libalkimia and also the testcases for it contained in alkvaluetest.cpp in method void AlkValueTest::convertDenominator(void) starting on line 426. Maybe, I should drop an example here: Let's say, the 'current value' of the MyMoneyMoney object is "1/2" (or in the decimal world: 0.5). The nominator is 1 and the denominator is 2. Calling convertDenominator(100) on this object will return a new AlkValue object with nominator 50 and denominator 100 (which still yields 0.5). Using 'valueRef().get_num()' returns the nominator as mpz_class object. Now the variable 'value' in the assignment contains '50' in our example, while d is 100. Continuing in the MyMoneyMoney code, the assignment of 'left' is the next part of interest. value is divided by the converted denominator and 50/100 is 0 (treated as an integers (mpz_class)) which is what we need left of the decimal symbol. 'right' will be assigned the result of "'current value' minus 'left' times the denomination we want": right = 0.5 - 0 * 100 = 50 The remainder - as you already noticed - is just a bit of string handling. Have a nice weekend. If you still need more information, please just ask. -- Regards Thomas Baumgart GPG-FP: E55E D592 F45F 116B 8429 4F99 9C59 DB40 B75D D3BA ------------------------------------------------------------- It is better to remain silent and be thought a fool, than to speak, and remove all doubt. -------------------------------------------------------------
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