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| From | "MikeWhy" <boat042-nospam@yahoo.com> |
|---|---|
| Newsgroups | comp.lang.c, comp.lang.c++ |
| Subject | Re: C/C++ pitfalls related to 64-bits (unsigned long & double) |
| Date | 2012-02-14 11:16 -0600 |
| Organization | A noiseless patient Spider |
| Message-ID | <jhe4sr$bo9$1@dont-email.me> (permalink) |
| References | (12 earlier) <jhcl3k$huq$1@news.albasani.net> <buod39i59dt.fsf@dhlpc061.dev.necel.com> <jhcuke$41l$1@news.albasani.net> <jhd7j6$k21$1@dont-email.me> <jhe19u$fi7$1@news.albasani.net> |
Cross-posted to 2 groups.
"BGB" <cr88192@hotmail.com> wrote in message
news:jhe19u$fi7$1@news.albasani.net...
> On 2/14/2012 1:56 AM, MikeWhy wrote:
>> The MSVC warnings are rather explicit:
>> "... possible loss of data".
>> 'initializing' : truncation from 'const uint_64' to 'const double'
>> 'initializing' : conversion from 'const double' to 'const uint_64',
>> possible loss of data
>>
>
> you sure we are talking about the same piece of code?...
> my example wasn't using any "uint_64", just a plain "int" type (which is
> 32 bits).
No, I'm not sure at all. At some point, the conversation turned it into
64-bit unsigned, possibly only in my head.
Both gcc and MSVC get this right:
const int_64 ifoo = -1LL;
{
double foox = ifoo;
uint_64 foo2 = foox;
std::cout << '(' << (uint_64)ifoo << " == " << foo2 << ") ==> "
<< ((uint_64)ifoo == foo2 ? "true" : "false")
<< '\n';
}
... but, both get the following wrong:
{
uint_64 foo = ifoo;
double foox = foo;
uint_64 foo2 = foox;
std::cout << '(' << foo << " == " << foo2 << ") ==> "
<< (foo == foo2 ? "true" : "false")
<< '\n';
}
gcc: (18446744073709551615 == 0) ==> false
MSVC: (18446744073709551615 == 9223372036854775808) ==> false
... and gcc gets it right if the values are marked const:
{
const uint_64 foo = ifoo;
const double foox = foo;
const uint_64 foo2 = foox;
std::cout << '(' << foo << " == " << foo2 << ") ==> "
<< (foo == foo2 ? "true" : "false")
<< '\n';
}
gcc: (18446744073709551615 == 18446744073709551615) ==> true
MSVC: (18446744073709551615 == 9223372036854775808) ==> false
gcc apparently keeps enough precision for the const double initializer
value, possibly as a long double. MSVC obviously does not.
All the same, both compilers print diagnostics about signed/unsigned
mismatches; possible loss of data in conversions; truncation/overflow in
conversion.
Back to comp.lang.c | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread
C/C++ pitfalls related to 64-bits (unsigned long & double) Alex Vinokur <alex.vinokur@gmail.com> - 2012-02-13 04:41 -0800
Re: C/C++ pitfalls related to 64-bits (unsigned long & double) Leigh Johnston <leigh@i42.co.uk> - 2012-02-13 12:49 +0000
Re: C/C++ pitfalls related to 64-bits (unsigned long & double) Alex Vinokur <alex.vinokur@gmail.com> - 2012-02-13 04:59 -0800
Re: C/C++ pitfalls related to 64-bits (unsigned long & double) Leigh Johnston <leigh@i42.co.uk> - 2012-02-13 13:07 +0000
Re: C/C++ pitfalls related to 64-bits (unsigned long & double) Goran <goran.pusic@gmail.com> - 2012-02-13 04:54 -0800
Re: C/C++ pitfalls related to 64-bits (unsigned long & double) Alex Vinokur <alex.vinokur@gmail.com> - 2012-02-13 05:00 -0800
Re: C/C++ pitfalls related to 64-bits (unsigned long & double) Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-02-13 13:27 +0000
Re: C/C++ pitfalls related to 64-bits (unsigned long & double) Goran <goran.pusic@gmail.com> - 2012-02-13 07:14 -0800
Re: C/C++ pitfalls related to 64-bits (unsigned long & double) Eric Sosman <esosman@ieee-dot-org.invalid> - 2012-02-13 08:14 -0500
Re: C/C++ pitfalls related to 64-bits (unsigned long & double) Eric Sosman <esosman@ieee-dot-org.invalid> - 2012-02-13 08:17 -0500
Re: C/C++ pitfalls related to 64-bits (unsigned long & double) glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2012-02-13 21:52 +0000
Re: C/C++ pitfalls related to 64-bits (unsigned long & double) James Kuyper <jameskuyper@verizon.net> - 2012-02-13 17:08 -0500
Re: C/C++ pitfalls related to 64-bits (unsigned long & double) Eric Sosman <esosman@ieee-dot-org.invalid> - 2012-02-13 20:44 -0500
Re: C/C++ pitfalls related to 64-bits (unsigned long & double) Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-02-13 13:16 +0000
Re: C/C++ pitfalls related to 64-bits (unsigned long & double) BGB <cr88192@hotmail.com> - 2012-02-13 11:18 -0700
Re: C/C++ pitfalls related to 64-bits (unsigned long & double) "MikeWhy" <boat042-nospam@yahoo.com> - 2012-02-13 15:18 -0600
Re: C/C++ pitfalls related to 64-bits (unsigned long & double) James Kuyper <jameskuyper@verizon.net> - 2012-02-13 16:26 -0500
Re: C/C++ pitfalls related to 64-bits (unsigned long & double) "MikeWhy" <boat042-nospam@yahoo.com> - 2012-02-13 16:05 -0600
Re: C/C++ pitfalls related to 64-bits (unsigned long & double) James Kuyper <jameskuyper@verizon.net> - 2012-02-13 17:13 -0500
Re: C/C++ pitfalls related to 64-bits (unsigned long & double) Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-02-13 23:35 +0000
Re: C/C++ pitfalls related to 64-bits (unsigned long & double) BGB <cr88192@hotmail.com> - 2012-02-13 17:25 -0700
Re: C/C++ pitfalls related to 64-bits (unsigned long & double) Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-02-14 01:45 +0000
Re: C/C++ pitfalls related to 64-bits (unsigned long & double) BGB <cr88192@hotmail.com> - 2012-02-13 18:55 -0700
Re: C/C++ pitfalls related to 64-bits (unsigned long & double) Miles Bader <miles@gnu.org> - 2012-02-14 11:51 +0900
Re: C/C++ pitfalls related to 64-bits (unsigned long & double) Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-02-14 03:13 +0000
Re: C/C++ pitfalls related to 64-bits (unsigned long & double) BGB <cr88192@hotmail.com> - 2012-02-13 20:39 -0700
Re: C/C++ pitfalls related to 64-bits (unsigned long & double) Miles Bader <miles@gnu.org> - 2012-02-14 13:25 +0900
Re: C/C++ pitfalls related to 64-bits (unsigned long & double) BGB <cr88192@hotmail.com> - 2012-02-13 23:22 -0700
Re: C/C++ pitfalls related to 64-bits (unsigned long & double) "MikeWhy" <boat042-nospam@yahoo.com> - 2012-02-14 02:56 -0600
Re: C/C++ pitfalls related to 64-bits (unsigned long & double) BGB <cr88192@hotmail.com> - 2012-02-14 09:13 -0700
Re: C/C++ pitfalls related to 64-bits (unsigned long & double) "MikeWhy" <boat042-nospam@yahoo.com> - 2012-02-14 11:16 -0600
Re: C/C++ pitfalls related to 64-bits (unsigned long & double) BGB <cr88192@hotmail.com> - 2012-02-14 12:27 -0700
Re: C/C++ pitfalls related to 64-bits (unsigned long & double) Eric Sosman <esosman@ieee-dot-org.invalid> - 2012-02-13 23:04 -0500
Re: C/C++ pitfalls related to 64-bits (unsigned long & double) Miles Bader <miles@gnu.org> - 2012-02-14 14:00 +0900
Re: C/C++ pitfalls related to 64-bits (unsigned long & double) Robert Wessel <robertwessel2@yahoo.com> - 2012-02-14 00:45 -0600
Re: C/C++ pitfalls related to 64-bits (unsigned long & double) glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2012-02-14 14:22 +0000
Re: C/C++ pitfalls related to 64-bits (unsigned long & double) Robert Wessel <robertwessel2@yahoo.com> - 2012-02-14 13:06 -0600
Re: C/C++ pitfalls related to 64-bits (unsigned long & double) BGB <cr88192@hotmail.com> - 2012-02-14 12:40 -0700
Re: C/C++ pitfalls related to 64-bits (unsigned long & double) James Kuyper <jameskuyper@verizon.net> - 2012-02-13 23:05 -0500
Re: C/C++ pitfalls related to 64-bits (unsigned long & double) Miles Bader <miles@gnu.org> - 2012-02-14 14:01 +0900
Re: C/C++ pitfalls related to 64-bits (unsigned long & double) Keith Thompson <kst-u@mib.org> - 2012-02-14 03:01 -0800
Re: C/C++ pitfalls related to 64-bits (unsigned long & double) Lowell Gilbert <lgusenet@be-well.ilk.org> - 2012-02-14 12:53 -0500
Re: C/C++ pitfalls related to 64-bits (unsigned long & double) James Kuyper <jameskuyper@verizon.net> - 2012-02-14 14:39 -0500
Re: C/C++ pitfalls related to 64-bits (unsigned long & double) jgk@panix.com (Joe keane) - 2012-02-14 20:45 +0000
Re: C/C++ pitfalls related to 64-bits (unsigned long & double) glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2012-02-14 22:57 +0000
Re: C/C++ pitfalls related to 64-bits (unsigned long & double) Keith Thompson <kst-u@mib.org> - 2012-02-14 15:38 -0800
Re: C/C++ pitfalls related to 64-bits (unsigned long & double) glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2012-02-15 00:22 +0000
Re: C/C++ pitfalls related to 64-bits (unsigned long & double) Robert Wessel <robertwessel2@yahoo.com> - 2012-02-15 00:39 -0600
Re: C/C++ pitfalls related to 64-bits (unsigned long & double) glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2012-02-15 08:00 +0000
Re: C/C++ pitfalls related to 64-bits (unsigned long & double) Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-02-13 22:00 +0000
Re: C/C++ pitfalls related to 64-bits (unsigned long & double) BGB <cr88192@hotmail.com> - 2012-02-13 17:04 -0700
Re: C/C++ pitfalls related to 64-bits (unsigned long & double) Malcolm McLean <malcolm.mclean5@btinternet.com> - 2012-02-13 16:15 -0800
Re: C/C++ pitfalls related to 64-bits (unsigned long & double) Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-02-14 00:46 +0000
Re: C/C++ pitfalls related to 64-bits (unsigned long & double) BGB <cr88192@hotmail.com> - 2012-02-13 18:31 -0700
Re: C/C++ pitfalls related to 64-bits (unsigned long & double) BGB <cr88192@hotmail.com> - 2012-02-13 18:41 -0700
Re: C/C++ pitfalls related to 64-bits (unsigned long & double) Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-02-14 02:33 +0000
Re: C/C++ pitfalls related to 64-bits (unsigned long & double) BGB <cr88192@hotmail.com> - 2012-02-13 20:20 -0700
Re: C/C++ pitfalls related to 64-bits (unsigned long & double) Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-02-14 03:26 +0000
Re: C/C++ pitfalls related to 64-bits (unsigned long & double) BGB <cr88192@hotmail.com> - 2012-02-13 20:49 -0700
Re: C/C++ pitfalls related to 64-bits (unsigned long & double) Robert Wessel <robertwessel2@yahoo.com> - 2012-02-14 00:24 -0600
Re: C/C++ pitfalls related to 64-bits (unsigned long & double) BGB <cr88192@hotmail.com> - 2012-02-13 23:42 -0700
Re: C/C++ pitfalls related to 64-bits (unsigned long & double) James Kuyper <jameskuyper@verizon.net> - 2012-02-14 06:48 -0500
Re: C/C++ pitfalls related to 64-bits (unsigned long & double) Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-02-14 13:51 +0000
Re: C/C++ pitfalls related to 64-bits (unsigned long & double) BGB <cr88192@hotmail.com> - 2012-02-14 08:42 -0700
Re: C/C++ pitfalls related to 64-bits (unsigned long & double) glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2012-02-14 19:58 +0000
Re: C/C++ pitfalls related to 64-bits (unsigned long & double) glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2012-02-14 14:27 +0000
Re: C/C++ pitfalls related to 64-bits (unsigned long & double) BGB <cr88192@hotmail.com> - 2012-02-14 09:10 -0700
Re: C/C++ pitfalls related to 64-bits (unsigned long & double) glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2012-02-14 20:02 +0000
Re: C/C++ pitfalls related to 64-bits (unsigned long & double) Noob <root@127.0.0.1> - 2012-02-13 15:22 +0100
Re: C/C++ pitfalls related to 64-bits (unsigned long & double) legalize+jeeves@mail.xmission.com (Richard) - 2012-02-13 18:49 +0000
Re: C/C++ pitfalls related to 64-bits (unsigned long & double) James Kuyper <jameskuyper@verizon.net> - 2012-02-13 13:55 -0500
Re: C/C++ pitfalls related to 64-bits (unsigned long & double) Juha Nieminen <nospam@thanks.invalid> - 2012-02-13 19:14 +0000
Re: C/C++ pitfalls related to 64-bits (unsigned long & double) Barry Schwarz <schwarzb@dqel.com> - 2012-02-13 12:14 -0800
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