Hexadecimal and stream element arrays
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From: Stephen Leake on 21 Apr 2010 08:38 "Jeffrey R. Carter" <ggsub(a)pragmada.x10hosting.com> writes: > On Apr 20, 12:25 am, Stephen Leake <stephen_le...(a)stephe-leake.org> > wrote: >> >> generic >> Width : Natural; >> type Number_Type is mod <>; >> function SAL.Generic_Hex_Image (Item : in Number_Type) return String; >> -- Return a hexadecimal image of Item, padded with leading zeros to >> -- Width. If Width is too small for Item, leading digits are silently >> -- truncated. > > So if I sometimes want different widths for the same type, I have to > have multiple instantiations? Yes. But in practice, the width you want is Number_Type'Width (but assuming hexadecimal), so it's not a problem. The only problem I've encountered is the "silently truncated" part. We changed a number type to have more bits, but forgot to change the Width parameter here. There are times, such as building formatted dates, when I need a specific number of characters, and want an exception if the actual value can't be represented in that number. Then this function is not appropriate. > That doesn't seem very friendly to me. I don't see why Width couldn't > be a parameter of the function, It could; in the body, it is only used as the size of the result image string. It's just historical accident that it is a generic parameter instead. > probably defaulted to Number_Type'Width. That assumes base 10, so it would be wrong. If I made a change like this, I'd keep the generic parameter as the default width, or add a function that computes a default width assuming base 16, and use that as the default. > What do I do for signed integer images, I never need to image signed integers in hex; that's confusing. > for bases other than 16, sal-generic_binary_image.ads sal-generic_decimal_image.ads are the only ones I've ever needed. The binary image includes '_' every four digits. > and for signed integer images for bases other than 16? Never needed them. > Do I have to roll my own for these cases? Yes. It is far easier to test a small, focused routine than a large, general purpose one. > In Ada.Text_IO, a Width of zero implies the minimum width needed to > represent the value; here it's an expensive way to get a null String. > I'd prefer consistency with the standard. If this function were proposed as part of the Ada standard, that would make sense. However, it is part of SAL, which often has a different philosophy. > I haven't used SAL, but these are the kind of comments you'd probably > get from me if I did use this function. HTH. Thanks for your comments. -- -- Stephe
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