On Sun, Jun 24, 2012 at 06:23:46PM +0200, jean-pierre charras wrote: > I am afraid I do not really understand your question. > In float to integer conversions, rounding creates a smaller error than > truncating. > And truncating fval < 0 ? fval - 0.5 : fval + 0.5 is the right way to round a > value that must be converted to integer BIU.
Right, I was asking before in other circumstances (i.e. motion control) truncation or rounding is often (I can't say always, but almost) replaced by floor()ing, to avoid a discontinuity issue around zero (reason: the default rounding minimized biasing, flooring minimizes discontinuities, more or less; I don't know the proper math terms...) I generally simply avoid floating point if possible using fixed point instead, if dynamic range is not needed; there is also the issue of the rounding mode in use and so on (wikipedia treats everything in details...). In short I asked because I have simply never seen that construction (but in fact maybe it's simply equivalent to floor(x+0.5) :P). Just to know better the code. > By the way, your recent issue when reading your board file in kicad nanometer > version is a truncating issue, > when scaling float values read in files to integer internal units. > When using rounding conversion instead of truncating, it happens no more. Wasn't that a precision issue caused by internal rounding of printf/scanf using doubles instead of long doubles? (I would have simply saved the nanos as integer...) If that was the case changing precision shouldn't have changed the result! Anyway, this is my view about float to int conversion: if possible, avoid it; otherwise just do whatever works (not very scientific, I know...) -- Lorenzo Marcantonio Logos Srl _______________________________________________ Mailing list: https://launchpad.net/~kicad-developers Post to : [email protected] Unsubscribe : https://launchpad.net/~kicad-developers More help : https://help.launchpad.net/ListHelp
