Re: signed is undefined and has been since 1992 (in GCC)

[Robert Dewar <dewar@adacore.com>]

Gabriel Dos Reis wrote:

> The issue here is whether if the hardware consistently display a
> semantics, GCC should not allow access to that consistent semantics
> under the name that "the standard says it is undefined behaviour".
> Consider the case of converting a void* to a F*, where F is a function
> type. 

Well the "hardware consistently displaying a semantics" is not so
cut and dried as you think (consider the loop instruction and other
arithmetic on the x86 for instance in the context of generating code
for loops).

THis is all about trading off undefined behavior (a bad thing) against
high performance (a good thing) against encouraging people to write
portable code (a good thing) against existing wrong programs working
(probably a good thing, though at odds with the portability requirement).

C is not a way of writing machine code, it is an abstract language
defined by the standard. There can be arguyments for language extension,
as you making, but such decisions should be made with proper data about
the magnitude of the tradeoffs.
> 
> -- Gaby