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Groups > comp.lang.c++ > #81788
| From | Manfred <noname@add.invalid> |
|---|---|
| Newsgroups | comp.lang.c++ |
| Subject | Re: How to get mantissa of long double? |
| Date | 2021-10-02 18:58 +0200 |
| Organization | Aioe.org NNTP Server |
| Message-ID | <sja34j$10k8$1@gioia.aioe.org> (permalink) |
| References | <c19306a0-c1ea-419e-9604-d0e124c358e0n@googlegroups.com> <sj7br6$qk2$1@gioia.aioe.org> <sj7ilh$6bk$1@dont-email.me> <838b5e50-a8f9-4bac-a034-7bd1e649ac27n@googlegroups.com> |
On 10/2/2021 2:23 AM, wij wrote:
> On Saturday, 2 October 2021 at 02:05:56 UTC+8, james...@alumni.caltech.edu wrote:
>> On 10/1/21 12:09 PM, Radica...@theburrow.co.uk wrote:
>>> On Fri, 1 Oct 2021 08:37:21 -0700 (PDT)
>>> wij <wyn...@gmail.com> wrote:
>>>> // numeric_limits<long double>::digits=64.
>>>> //
>>>> typedef long double FType;
>>>> FType x=numeric_limits<FType>::max();
>>>> int iexp;
>>>> int64_t mint;
>>>> x=::frexpl(x,&iexp);
>>>> x=::ldexpl(x,numeric_limits<FType>::digits);
>>>> mint= static_cast<int64_t>(x);
>>>>
>>>> Result (mint) is a negative number, something not right!!!
>> I can't duplicate this problem: I get mint:9223372036854775807.
<snip>
>
> // ----- file t.cpp -----
> #include <math.h>
> #include <limits>
> #include <iostream>
>
> using namespace std;
> #define ENDL endl
>
> template<typename T>
> int64_t get_mant(T x) {
> int iexp;
> x=frexp(x,&iexp);
> x=ldexp(x,numeric_limits<T>::digits);
> return static_cast<int64_t>(x);
> };
>
> int main()
> {
> cout << dec << get_mant(numeric_limits<float>::max()) << ", "
> << hex << get_mant(numeric_limits<float>::max()) << ENDL;
> cout << dec << get_mant(numeric_limits<double>::max()) << ", "
> << hex << get_mant(numeric_limits<double>::max()) << ENDL;
> cout << dec << get_mant(numeric_limits<long double>::max()) << ", "
> << hex << get_mant(numeric_limits<long double>::max()) << ENDL;
> return 0;
> };
> // end file t.cpp -----
>
> $ g++ t.cpp
> ]$ ./a.out
> 16777215, ffffff
> 9007199254740991, 1fffffffffffff
> -9223372036854775808, 8000000000000000
>
There are two problems:
1)
The templated function uses 'frexp' and 'ldexp', which take both double
arguments (not *long* double), hence UB occurs at those calls for the
'long double' type whenever this type is actually larger than 'double'.
2)
On my Linux box numeric_limits<*long* double>::digits is 64
(numeric_limits<double>::digits is 53), so the static_cast<int64_t>(x)
yields UB again.
=========
#include <cmath>
#include <limits>
#include <iostream>
using namespace std;
#define ENDL endl
uint64_t get_mantf(float x)
{
int iexp;
x=frexp(x,&iexp);
x=ldexp(x,numeric_limits<float>::digits);
return static_cast<uint64_t>(x);
};
uint64_t get_mant(double x)
{
int iexp;
x=frexp(x,&iexp);
x=ldexp(x,numeric_limits<double>::digits);
return static_cast<uint64_t>(x);
};
uint64_t get_mantl(long double x)
{
int iexp;
x=frexp(x,&iexp);
x=ldexp(x,numeric_limits<long double>::digits);
return static_cast<uint64_t>(x);
};
int main()
{
cout << dec << numeric_limits<float>::digits << ", " <<
get_mantf(numeric_limits<float>::max()) << ", "
<< hex << get_mantf(numeric_limits<float>::max()) << ENDL;
cout << dec << numeric_limits<double>::digits << ", " <<
get_mant(numeric_limits<double>::max()) << ", "
<< hex << get_mant(numeric_limits<double>::max()) << ENDL;
cout << dec << numeric_limits<long double>::digits << ", " <<
get_mantl(numeric_limits<long double>::max()) << ", "
<< hex << get_mantl(numeric_limits<long double>::max()) << ENDL;
return 0;
}
===================
$ c++ -std=c++11 -O2 -Wall mant.cc && ./a.out
24, 16777215, ffffff
53, 9007199254740991, 1fffffffffffff
64, 18446744073709551615, ffffffffffffffff
Back to comp.lang.c++ | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread
How to get mantissa of long double? wij <wyniijj@gmail.com> - 2021-10-01 08:37 -0700
Re: How to get mantissa of long double? RadicalRabbit@theburrow.co.uk - 2021-10-01 16:09 +0000
Re: How to get mantissa of long double? James Kuyper <jameskuyper@alumni.caltech.edu> - 2021-10-01 14:05 -0400
Re: How to get mantissa of long double? wij <wyniijj@gmail.com> - 2021-10-01 17:23 -0700
Re: How to get mantissa of long double? Manfred <noname@add.invalid> - 2021-10-02 18:58 +0200
Re: How to get mantissa of long double? Manfred <noname@add.invalid> - 2021-10-02 19:21 +0200
Re: How to get mantissa of long double? Bonita Montero <Bonita.Montero@gmail.com> - 2021-10-01 19:18 +0200
Re: How to get mantissa of long double? Bonita Montero <Bonita.Montero@gmail.com> - 2021-10-01 19:20 +0200
Re: How to get mantissa of long double? Bonita Montero <Bonita.Montero@gmail.com> - 2021-10-01 19:25 +0200
Re: How to get mantissa of long double? Bonita Montero <Bonita.Montero@gmail.com> - 2021-10-01 19:53 +0200
Re: How to get mantissa of long double? Bonita Montero <Bonita.Montero@gmail.com> - 2021-10-03 08:09 +0200
Re: How to get mantissa of long double? Bart <bc@freeuk.com> - 2021-10-03 11:15 +0100
Re: How to get mantissa of long double? Bonita Montero <Bonita.Montero@gmail.com> - 2021-10-03 12:19 +0200
Re: How to get mantissa of long double? red floyd <no.spam@its.invalid> - 2021-10-03 18:03 -0700
Re: How to get mantissa of long double? David Brown <david.brown@hesbynett.no> - 2021-10-04 09:52 +0200
Re: How to get mantissa of long double? Juha Nieminen <nospam@thanks.invalid> - 2021-10-04 09:59 +0000
Re: How to get mantissa of long double? Bonita Montero <Bonita.Montero@gmail.com> - 2021-10-04 13:50 +0200
Re: How to get mantissa of long double? David Brown <david.brown@hesbynett.no> - 2021-10-04 20:04 +0200
Re: How to get mantissa of long double? Bonita Montero <Bonita.Montero@gmail.com> - 2021-10-05 07:12 +0200
Re: How to get mantissa of long double? David Brown <david.brown@hesbynett.no> - 2021-10-05 09:47 +0200
Re: How to get mantissa of long double? Bonita Montero <Bonita.Montero@gmail.com> - 2021-10-05 16:46 +0200
Re: How to get mantissa of long double? David Brown <david.brown@hesbynett.no> - 2021-10-05 19:04 +0200
Re: How to get mantissa of long double? Bonita Montero <Bonita.Montero@gmail.com> - 2021-10-05 19:13 +0200
Re: How to get mantissa of long double? Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2021-10-05 09:04 -0700
Re: How to get mantissa of long double? Bonita Montero <Bonita.Montero@gmail.com> - 2021-10-05 19:14 +0200
Re: How to get mantissa of long double? Bart <bc@freeuk.com> - 2021-10-05 19:21 +0100
Re: How to get mantissa of long double? Bonita Montero <Bonita.Montero@gmail.com> - 2021-10-06 07:58 +0200
Re: How to get mantissa of long double? David Brown <david.brown@hesbynett.no> - 2021-10-06 08:11 +0200
Re: How to get mantissa of long double? Bonita Montero <Bonita.Montero@gmail.com> - 2021-10-06 10:25 +0200
Re: How to get mantissa of long double? scott@slp53.sl.home (Scott Lurndal) - 2021-10-06 14:25 +0000
Re: How to get mantissa of long double? Bonita Montero <Bonita.Montero@gmail.com> - 2021-10-06 16:53 +0200
Re: How to get mantissa of long double? Bart <bc@freeuk.com> - 2021-10-06 12:12 +0100
Re: How to get mantissa of long double? Bonita Montero <Bonita.Montero@gmail.com> - 2021-10-06 14:48 +0200
Re: How to get mantissa of long double? red floyd <no.spam.here@its.invalid> - 2021-10-06 09:44 -0700
Re: How to get mantissa of long double? Bonita Montero <Bonita.Montero@gmail.com> - 2021-10-06 18:52 +0200
Re: How to get mantissa of long double? Bonita Montero <Bonita.Montero@gmail.com> - 2021-10-06 19:02 +0200
Re: How to get mantissa of long double? Juha Nieminen <nospam@thanks.invalid> - 2021-10-07 05:35 +0000
Re: How to get mantissa of long double? David Brown <david.brown@hesbynett.no> - 2021-10-07 08:20 +0200
Re: How to get mantissa of long double? Bonita Montero <Bonita.Montero@gmail.com> - 2021-10-07 08:38 +0200
Re: How to get mantissa of long double? Bonita Montero <Bonita.Montero@gmail.com> - 2021-10-07 08:42 +0200
Re: How to get mantissa of long double? David Brown <david.brown@hesbynett.no> - 2021-10-07 10:23 +0200
Re: How to get mantissa of long double? Bonita Montero <Bonita.Montero@gmail.com> - 2021-10-08 20:23 +0200
Re: How to get mantissa of long double? David Brown <david.brown@hesbynett.no> - 2021-10-09 10:23 +0200
Re: How to get mantissa of long double? Bonita Montero <Bonita.Montero@gmail.com> - 2021-10-09 10:50 +0200
Re: How to get mantissa of long double? Branimir Maksimovic <branimir.maksimovic@icloud.com> - 2021-10-09 09:02 +0000
Re: How to get mantissa of long double? scott@slp53.sl.home (Scott Lurndal) - 2021-10-09 14:57 +0000
Re: How to get mantissa of long double? Bart <bc@freeuk.com> - 2021-10-09 12:16 +0100
Re: How to get mantissa of long double? David Brown <david.brown@hesbynett.no> - 2021-10-09 15:10 +0200
Re: How to get mantissa of long double? red floyd <no.spam.here@its.invalid> - 2021-10-09 10:26 -0700
Re: How to get mantissa of long double? Vir Campestris <vir.campestris@invalid.invalid> - 2021-10-12 21:23 +0100
Re: How to get mantissa of long double? RadicalRabbit@theburrow.co.uk - 2021-10-13 10:30 +0000
Re: How to get mantissa of long double? Bonita Montero <Bonita.Montero@gmail.com> - 2021-10-07 08:38 +0200
Re: How to get mantissa of long double? Juha Nieminen <nospam@thanks.invalid> - 2021-10-08 04:37 +0000
Re: How to get mantissa of long double? Bonita Montero <Bonita.Montero@gmail.com> - 2021-10-08 07:54 +0200
Re: How to get mantissa of long double? red floyd <no.spam.here@its.invalid> - 2021-10-07 22:44 -0700
Re: How to get mantissa of long double? David Brown <david.brown@hesbynett.no> - 2021-10-07 08:17 +0200
Re: How to get mantissa of long double? Juha Nieminen <nospam@thanks.invalid> - 2021-10-08 04:39 +0000
Re: How to get mantissa of long double? David Brown <david.brown@hesbynett.no> - 2021-10-08 09:25 +0200
Re: How to get mantissa of long double? scott@slp53.sl.home (Scott Lurndal) - 2021-10-08 14:34 +0000
Re: How to get mantissa of long double? "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2021-10-06 13:57 -0700
Re: How to get mantissa of long double? Branimir Maksimovic <branimir.maksimovic@icloud.com> - 2021-10-05 19:34 +0000
Re: How to get mantissa of long double? Branimir Maksimovic <branimir.maksimovic@icloud.com> - 2021-10-05 19:33 +0000
Re: How to get mantissa of long double? Branimir Maksimovic <branimir.maksimovic@icloud.com> - 2021-10-05 10:19 +0000
Re: How to get mantissa of long double? Bart <bc@freeuk.com> - 2021-10-04 14:06 +0100
Re: How to get mantissa of long double? Bonita Montero <Bonita.Montero@gmail.com> - 2021-10-04 16:12 +0200
Re: How to get mantissa of long double? Branimir Maksimovic <branimir.maksimovic@icloud.com> - 2021-10-04 16:15 +0000
Re: How to get mantissa of long double? Branimir Maksimovic <branimir.maksimovic@icloud.com> - 2021-10-04 16:15 +0000
Re: How to get mantissa of long double? David Brown <david.brown@hesbynett.no> - 2021-10-05 09:48 +0200
Re: How to get mantissa of long double? Juha Nieminen <nospam@thanks.invalid> - 2021-10-05 05:19 +0000
Re: How to get mantissa of long double? David Brown <david.brown@hesbynett.no> - 2021-10-05 10:00 +0200
Re: How to get mantissa of long double? Bonita Montero <Bonita.Montero@gmail.com> - 2021-10-05 16:47 +0200
Re: How to get mantissa of long double? scott@slp53.sl.home (Scott Lurndal) - 2021-10-04 14:37 +0000
Re: How to get mantissa of long double? Bonita Montero <Bonita.Montero@gmail.com> - 2021-10-04 16:53 +0200
Re: How to get mantissa of long double? scott@slp53.sl.home (Scott Lurndal) - 2021-10-04 17:08 +0000
Re: How to get mantissa of long double? Bart <bc@freeuk.com> - 2021-10-04 20:22 +0100
Re: How to get mantissa of long double? Bart <bc@freeuk.com> - 2021-10-01 19:09 +0100
Re: How to get mantissa of long double? Bonita Montero <Bonita.Montero@gmail.com> - 2021-10-01 20:16 +0200
Re: How to get mantissa of long double? Branimir Maksimovic <branimir.maksimovic@icloud.com> - 2021-10-01 18:53 +0000
Re: How to get mantissa of long double? James Kuyper <jameskuyper@alumni.caltech.edu> - 2021-10-01 20:19 -0400
Re: How to get mantissa of long double? Branimir Maksimovic <branimir.maksimovic@icloud.com> - 2021-10-02 02:16 +0000
Re: How to get mantissa of long double? James Kuyper <jameskuyper@alumni.caltech.edu> - 2021-10-02 01:28 -0400
Re: How to get mantissa of long double? James Kuyper <jameskuyper@alumni.caltech.edu> - 2021-10-02 01:56 -0400
Re: How to get mantissa of long double? Branimir Maksimovic <branimir.maksimovic@icloud.com> - 2021-10-02 10:59 +0000
Re: How to get mantissa of long double? James Kuyper <jameskuyper@alumni.caltech.edu> - 2021-10-02 14:57 -0400
Re: How to get mantissa of long double? James Kuyper <jameskuyper@alumni.caltech.edu> - 2021-10-02 15:37 -0400
Re: How to get mantissa of long double? Branimir Maksimovic <branimir.maksimovic@icloud.com> - 2021-10-03 00:47 +0000
Re: How to get mantissa of long double? James Kuyper <jameskuyper@alumni.caltech.edu> - 2021-10-03 23:42 -0400
Re: How to get mantissa of long double? Branimir Maksimovic <branimir.maksimovic@icloud.com> - 2021-10-04 04:35 +0000
Re: How to get mantissa of long double? Bonita Montero <Bonita.Montero@gmail.com> - 2021-10-02 12:09 +0200
Re: How to get mantissa of long double? "Alf P. Steinbach" <alf.p.steinbach@gmail.com> - 2021-10-02 21:00 +0200
Re: How to get mantissa of long double? James Kuyper <jameskuyper@alumni.caltech.edu> - 2021-10-02 15:12 -0400
Re: How to get mantissa of long double? "Alf P. Steinbach" <alf.p.steinbach@gmail.com> - 2021-10-02 21:23 +0200
Re: How to get mantissa of long double? "Alf P. Steinbach" <alf.p.steinbach@gmail.com> - 2021-10-02 21:27 +0200
Re: How to get mantissa of long double? Manfred <noname@add.invalid> - 2021-10-02 23:19 +0200
Re: How to get mantissa of long double? James Kuyper <jameskuyper@alumni.caltech.edu> - 2021-10-03 23:43 -0400
Re: How to get mantissa of long double? Branimir Maksimovic <branimir.maksimovic@icloud.com> - 2021-10-03 00:45 +0000
Re: How to get mantissa of long double? James Kuyper <jameskuyper@alumni.caltech.edu> - 2021-10-03 23:31 -0400
Re: How to get mantissa of long double? Branimir Maksimovic <branimir.maksimovic@icloud.com> - 2021-10-04 04:34 +0000
Re: How to get mantissa of long double? James Kuyper <jameskuyper@alumni.caltech.edu> - 2021-10-04 11:30 -0400
Re: How to get mantissa of long double? Branimir Maksimovic <branimir.maksimovic@icloud.com> - 2021-10-04 16:19 +0000
Re: How to get mantissa of long double? wij <wyniijj@gmail.com> - 2021-10-03 00:35 -0700
Re: How to get mantissa of long double? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2021-10-03 15:02 +0100
Re: How to get mantissa of long double? wij <wyniijj@gmail.com> - 2021-10-03 18:46 -0700
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