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 Re: l3fp and sin(pi), cos(pi/2) Bruno Le Floch <[log in to unmask]> Tue, 27 May 2014 09:42:48 -0400 text/plain (33 lines) Hello Will, > about the typesetting; should/can we provide an easy way to typeset negative > zero just as zero? I suppose there are two cases where one needs to display numbers: for typesetting, and when writing to a file (terminal, log,...). For the first case, I'd advocate using siunitx, which has all the settings you may want, and more. For the second case, I feel that in all contexts where 0 is better than -0 (e.g. pdf specials) there is also a need to limit the number of significant digits to less than 16. This requires rounding. We should provide formatting functions which produce a string of characters from floating points. Doing this correctly is a bit subtle, and it is not clear what should be implemented and what can be left out (see e.g. http://www.cplusplus.com/reference/cstdio/printf/ for a long list of things C++ does). > When I was trying it out, I thought perhaps that \fp_eval:n would return > negative zero but \fp_to_decimal:n would “normalise” it; is that a crazy > idea? I'm not keen on that, but I don't have a very strong argument against it. Mainly, -0 is the correct result, so I don't see what's wrong with it. Actually... thinking about it, there is an easy way to get 0 for -0: add +0 to it. It turns out that 0+(-0) = +0, so for all x, 0+x is exactly x, except when x is -0, then 0+x is +0. If I remember correctly, the signs of (±0)±(±0) are not mandated by the standard, so we could presumably document that 0+x does the right thing, and make sure that this is mentioned in the code and tested. Bruno