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digitalmars.D.learn - Is integer overflow defined?

reply Sean Eskapp <eatingstaples gmail.com> writes:
Is integer overflow defined (for instance, as being mod 2^size)? Can I
reliably say that -long.min == 0L?
Sep 01 2011
parent reply Timon Gehr <timon.gehr gmx.ch> writes:
On 09/01/2011 06:20 PM, Sean Eskapp wrote:

 Is integer overflow defined (for instance, as being mod 2^size)?



I am quite sure that all operations are defined as operations on two's 
complement integers, which would mean overflow is defined, but I cannot 
find the respective part of the specification...


 Can I reliably say that -long.min == 0L?



Well no, -long.min == long.min .

according to TDPL p53., that fact is defined. (unary minus: -x == ~x+1)
Sep 01 2011
next sibling parent Sean Eskapp <eatingstaples gmail.com> writes:
== Quote from Timon Gehr (timon.gehr gmx.ch)'s article

 On 09/01/2011 06:20 PM, Sean Eskapp wrote:

 Is integer overflow defined (for instance, as being mod 2^size)?



 complement integers, which would mean overflow is defined, but I cannot
 find the respective part of the specification...
  > Can I reliably say that -long.min == 0L?
 Well no, -long.min == long.min .
 according to TDPL p53., that fact is defined. (unary minus: -x == ~x+1)



Ah, good points, thanks!
Sep 01 2011
prev sibling parent reply bearophile <bearophileHUGS lycos.com> writes:
Timon Gehr:


 according to TDPL p53., that fact is defined. (unary minus: -x == ~x+1)



Uhmmmm.

Bye,
bearophile
Sep 01 2011
parent Timon Gehr <timon.gehr gmx.ch> writes:
On 09/02/2011 02:45 AM, bearophile wrote:

 Timon Gehr:


 according to TDPL p53., that fact is defined. (unary minus: -x == ~x+1)



 Uhmmmm.

 Bye,
 bearophile



For unsigned integers it is clearly defined:

1000... => 0111... => 1000...

And according to TDPL p53: "This manipulation does not raise particular 
questions about the signedness of val".

So, it is guaranteed that it will work for long.min .
Sep 02 2011