[Bug other/60843] New: Documentation: 4.5 Integers/C99 6.3.1.3 ("reduce modulo 2^N")

["kdevel at vogtner dot de" <gcc-bugzilla@gcc.gnu.org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60843

            Bug ID: 60843
           Summary: Documentation: 4.5 Integers/C99 6.3.1.3 ("reduce
                    modulo 2^N")
           Product: gcc
           Version: 4.8.2
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: other
          Assignee: unassigned at gcc dot gnu.org
          Reporter: kdevel at vogtner dot de

Section 4.5 states [1]:

"The result of, or the signal raised by, converting an integer to a signed
integer type when the value cannot be represented in an object of that type
(C90 6.2.1.2, C99 6.3.1.3).

For conversion to a type of width N, the value is reduced modulo 2^N to be
within range of the type; no signal is raised."

Reduce A modulo M usually means find the least integer R in the range [0, M -
1] such that A is congruent R modulo M. But this is not what gcc compiled
programs do on i686/x86_64: One finds e.g. (int) 2147483649u == -2147483647.
The original bits are taken "as is", which equivalents to *subtraction* of 2^N
(N=32) giving -2147483647.

[1] http://gcc.gnu.org/onlinedocs/gcc-4.8.2/gcc/Integers-implementation.html