Re: Integer division specification

"=?iso-8859-1?q?Daniel_Kr=FCgler?=" <>
Tue, 20 Feb 2007 12:05:32 CST
On 17 Feb., 20:37, Gennaro Prota <> wrote:

On Wed, 14 Feb 2007 09:25:30 CST, Gennaro Prota wrote:


I was wondering if, as part of the synchronization with C99, the C++
standard is going to require truncation towards zero for integer
division or continue to allow the same choice as C90.

Well, let me please do another attempt at getting a reply. I have a
defect report concerning the specification of operator / and the
proposed resolution would depend on whether truncation "towards -inf"
is allowed or not.

It would help everyone, not least the committee which would have to
examine the DR, to know the answer to this (if it is already known

I'm sorry, that I can be only of limited help here, but even some
little help is better than nothing, I guess ;-)

I just read the current wording of C99 and the most recent draft for
C++. From what I read, I would deduce the following:

1) C99 (More exactly: I have studied 9899:1999 (E) for this), says
in 6.5.5/6:

"When integers are divided, the result of the / operator is the
quotient with any fractional part discarded.87)"

with footnote 87:

"This is often called ''truncation toward zero''."

so indeed C99 demands truncation toward zero.

2) Opposed to this, N2134 says in 5.6/4:

"If both operands are nonnegative then the remainder is nonnegative;
if not, the sign of the remainder is implementation-defined78)"

with footnote 78:

"According to work underway toward the revision of ISO C, the
algorithm for integer division follows the rules defined in the ISO
standard, ISO/IEC 1539:1991, in which the quotient is always rounded
toward zero."

So viewing from the Status Quo I interpret that our C++ Standard does
currently would allow any rounding strategy (including truncation
"towards -inf") if one of the operands is negative.

I cannot say, whether the current state of affairs are by design or
but the synchronization seems to be useful for most programmers.

Greetings from Bremen,


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