Hi Laurent, On Wednesday 22 February 2006 12:34, Laurent GUERBY wrote: > On Wed, 2006-02-22 at 10:54 +0100, Richard Guenther wrote: > > > > > > 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 > > > > Is the final "conversion" a checked conversion or an unchecked conversion? > > I.e. > > are we supposed to check for overflow using 'Valid on the final result? Or > > will > > the value be truncated or a runtime error raised? > > In the full language we are supposed to check the range on the > assignement and raise the predefined exception "CONSTRAINT_ERROR" if it > fails (whatever the way in the generated code). However GNAT by default > does not generate this kind of check, you need to add -gnato to the > compile flags.
my understanding is that -gnato causes the compiler to insert checks that the "100+X-X" computation does not overflow the base type. The compiler always inserts a check that the result is in the range of the target type T before performing the assignment, regardless of whether -gnato is set or not. Best wishes, Duncan.
