Re: [PATCH 0/3] yacc: compute the best type for the state number

[Hans Åberg]

> On 7 Oct 2019, at 07:15, Akim Demaille <address@hidden> wrote:
> 
>> Le 2 oct. 2019 à 15:58, Paul Eggert <address@hidden> a écrit :
>> 
>> On 10/1/19 10:27 PM, Akim Demaille wrote:
>>> I don't understand why you shy away from -128 and -32768 though.
>> 
>> The C Standard doesn't guarantee support for -128 and -32768. This 
>> originally was for ones' complement machines such as the Unisys ClearPath 
>> Dorado enterprise servers (still in use via firmware translation to Intel 
>> Xeon, and they have a C compiler),
> 
> Wow!  I was unaware of this.  Ain't it this kind of machines that is still in 
> use to run ancient COBOL programs?  Are they still used in production for 
> programs written in C?

The C/C++ compiler is still allowed to use it for optimizations, even though 
all current hardware I think use modulo 2^k representations; there is an 
example here:
http://blog.llvm.org/2011/05/what-every-c-programmer-should-know.html#signed_overflow

Then this links gives an example how the optimizer can remove an overflow 
check, causing a security issue:
http://blog.llvm.org/2011/05/what-every-c-programmer-should-know_14.html