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Re: Do C++ signed types have modulo semantics?

From: Mark Mitchell <mark at codesourcery dot com>
To: Michael Veksler <VEKSLER at il dot ibm dot com>
Cc: Paul Koning <pkoning at equallogic dot com>, gcc at gcc dot gnu dot org, gdr at integrable-solutions dot net, nathan at codesourcery dot com
Date: Mon, 27 Jun 2005 20:05:48 -0700
Subject: Re: Do C++ signed types have modulo semantics?
References: <OFF89CA957.1E322A19-ONC225702D.0052A8AF-C225702D.00546B33@il.ibm.com>

Michael Veksler wrote:

Most programmers "know" that arithmetic is modulo wordsize.  And those few
who know the right answer (only unsigned arithmetic is modulo) will
from time to time slip up and omit the "unsigned" keyword in their
declarations.

I agree.

Although the standard clearly makes signed overflow undefined, I think it would be better if GCC defined it to be modulo arithmetic. The degree to which that would result in inferior code seems likely to be somewhat small, and the amount of user confusion we would eliminate, and the number of programs that would not break with GCC, even though they work with other compilers, seems likely to be high.

--
Mark Mitchell
CodeSourcery, LLC
mark@codesourcery.com
(916) 791-8304

Follow-Ups:
- Re: Do C++ signed types have modulo semantics?
  - From: Gabriel Dos Reis
- Re: Do C++ signed types have modulo semantics?
  - From: Robert Dewar
- Re: Do C++ signed types have modulo semantics?
  - From: Joe Buck

References:
- Re: Do C++ signed types have modulo semantics?
  - From: Michael Veksler

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