On 2/20/06, Jeffrey A Law <[EMAIL PROTECTED]> wrote: > On Sun, 2006-02-19 at 20:43 +0100, Laurent GUERBY wrote: > > On Sun, 2006-02-19 at 14:23 -0500, Richard Kenner wrote: > > > "Second, for a given integer type (such as > > > natural___XDLU_0_2147483647), the type for the nodes in TYPE_MIN_VALUE > > > and TYPE_MAX_VALUE really should be a natural___XDLU_0_2147483647. > > > ie, the type of an integer constant should be the same as the type of > > > its min/max values." > > > > > > No, the type of the bounds of a subtype should be the *base type*. That's > > > how the tree has always looked, as far back as I can remember. > > > > This is because intermediate computations can produce results > > outside the subtype range but within the base type range (RM 3.5(6)), > > right? > > > > type T1 is range 0 .. 127; > > -- Compiler will choose some type for T'Base, likely to be -128..127 > > -- but could be Integer (implementation dependant) > > subtype T is T1 range 0 .. 100; > > R : T := 100+X-X; > > -- guaranteed work as long 100+X<=T'Base'Last and 100-X>=T'Base'First > Which leaves us with a very fundamental issue. Namely that we can not > use TYPE_MIN_VALUE or TYPE_MAX_VALUE for ranges. That's lame, > incredibly lame. This nonsense really should be isolated within the > Ada front-end.
Indeed. Ada should in this case generate R = (T)( (basetype)100 + (basetype)X - (basetype)X ) i.e. carry out all arithmetic explicitly in the basetype and only for stores and loads use the subtype. Otherwise we might as well get rid of TYPE_MIN_VALUE and TYPE_MAX_VALUE (for Ada). Richard.
