Hi Christian, On Mon, 2008-09-01 at 22:57 +0200, Christian Stimming wrote: > Am Montag, 1. September 2008 22:44 schrieb Charles Day: > > > > + fraction = converted_val.denom; > > > > + if (fraction <= 0) > > > > + return FALSE; > > > > > > out of curiosity, what is the reason for disallowing negative > > > denominators? > > My immediate reaction to this question: Denominators should be positive so > that a comparison of equal numbers gives predictable results, and also to > avoid any confusion about the actual meaning of a negative denominator. > > > > I am not sure whether there is a gnc_numeric API function > > > to switch signs of nom and denom safely, but I am sure that doing it is > > > possible :-) But maybe the current behavior is actually desired. > > > > Honestly, I'm not 100% sure what negative denominators mean. The function I > > added is essentially a modified version of is_decimal_fraction() from > > app-utils/gnc-ui-utils.c, and since negative denominators were not > > considered decimal numbers there, I did the same. > > > > On the other hand, I believe that a negative denominator of -3 may actually > > mean a denominator equal to 1/3. So if a gnc_numeric of 5/-3 is equal to > > 5/(1/3), then that is also equal to 5*3=15. > > Uh oh? No, not at all, please. A negative denominator must mean at most that > the sign of the rational number is changed from positive to negative, or, if > the numerator is negative as well, the sign of the number is changed from > negative to positive. No more, no less. As this doesn't make much sense, it > is sensible to restrict the denominator to positive numbers only.
I understand that negative denominators might look bewildering to some, but given the current API, one can _create(5, -1) such a number, _check() it and get an _OK. If there is a really made such a distinction in the other functions, then I guess a comment would be nice and appropriate conversion in _create almost necessary. Just my 2¢. > For sure negative numbers will and must never suddently turn into the inverse > of a number. Negative != inverted. Really. Always. > > Or did I miss anything here? I do not hope so :) Ciao, -- andi5
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