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Groups > comp.lang.c++ > #81702 > unrolled thread
| Started by | wij <wyniijj@gmail.com> |
|---|---|
| First post | 2021-10-01 08:37 -0700 |
| Last post | 2021-10-03 18:46 -0700 |
| Articles | 3 on this page of 103 — 17 participants |
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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
Page 6 of 6 — ← Prev page 1 2 3 4 5 [6]
| From | wij <wyniijj@gmail.com> |
|---|---|
| Date | 2021-10-03 00:35 -0700 |
| Message-ID | <ff4c206e-f6a6-47a4-8f52-829bd8254aaen@googlegroups.com> |
| In reply to | #81791 |
On Sunday, 3 October 2021 at 03:00:58 UTC+8, Alf P. Steinbach wrote: > On 1 Oct 2021 17:37, wij 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!!! > Apparently you're trying to obtain the bits of the mantissa of a `long > double` number, represented as an `int64_t` value. > > A `long double` is in practice either IEEE 754 64-bit, or IEEE 754 > 80-bit. In Windows that choice depends on the compiler. With Visual C++ > (and hence probably also Intel) it's 64-bit, same as type `double`, > while with MinGW g++ (and hence probably also clang) it 80-bit, > originally the x86-family's math coprocessor's extended format. For > 80-bit IEEE 754 the mantissa part is 64 bits. > > With 64-bits mantissa there is a high chance of setting the sign bit of > an `int64_t` to 1, resulting in a negative value. I believe that that > will only /not/ happen for a denormal value, but, I'm tired and might be > wrong about that. Anyway, instead use unsigned types for bit handling. > For example, in this case, use `uint64_t`. > > However, instead of the shenanigans with `frexpl` and `ldexpl` I'd just > use `memcpy`. > > Due to the silliness in gcc regarding the standard's "strict aliasing" > rule, I'd not use a reinterpretation pointer cast. > > > - Alf I changed int64_t to uint64_t, my problem is solved, thanks. (in the original post, the include file <math.h> should be <cmath>)
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| From | Ben Bacarisse <ben.usenet@bsb.me.uk> |
|---|---|
| Date | 2021-10-03 15:02 +0100 |
| Message-ID | <871r52fbq6.fsf@bsb.me.uk> |
| In reply to | #81702 |
I've not been following the details of the thread but it seems to have
strayed from the original question (as happens of course).
wij <wyniijj@gmail.com> writes:
> // 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!!!
frexp (et. al.) return a signed result with a magnitude in the interval
[1/2, 1). If you want the 64 most significant digits of the mantissa of
a long double (it may have many more digits than that) then I'd go for
something like this:
uint_least64_t ms64bits(long double d)
{
int exp;
return (uint_least64_t)std::scalbn(std::fabs(std::frexp(d, &exp)), 64);
}
If, as your code sketch suggests, you want all of them, then you are out
of luck as far as portable code goes because there may not be an integer
type wide enough.
But why do you want an integer value? For most mathematical uses the
result of std::frexp is what you really want.
--
Ben.
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| From | wij <wyniijj@gmail.com> |
|---|---|
| Date | 2021-10-03 18:46 -0700 |
| Message-ID | <5ee114d8-6f34-4d64-b92a-8710f9a1f099n@googlegroups.com> |
| In reply to | #81807 |
On Sunday, 3 October 2021 at 22:02:25 UTC+8, Ben Bacarisse wrote:
> I've not been following the details of the thread but it seems to have
> strayed from the original question (as happens of course).
> wij <wyn...@gmail.com> writes:
>
> > // 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!!!
> frexp (et. al.) return a signed result with a magnitude in the interval
> [1/2, 1). If you want the 64 most significant digits of the mantissa of
> a long double (it may have many more digits than that) then I'd go for
> something like this:
>
> uint_least64_t ms64bits(long double d)
> {
> int exp;
> return (uint_least64_t)std::scalbn(std::fabs(std::frexp(d, &exp)), 64);
> }
>
> If, as your code sketch suggests, you want all of them, then you are out
> of luck as far as portable code goes because there may not be an integer
> type wide enough.
>
> But why do you want an integer value? For most mathematical uses the
> result of std::frexp is what you really want.
>
> --
> Ben.
// --- Here is the real codes
explicit VLFloat(long double x) try {
typedef long double FType;
typedef uint64_t UIntMant;
WY_ENSURE(Limits<FType>::Bits<=CHAR_BIT*sizeof(UIntMant));
if(Wy::isfinite(x)==false) {
throw Errno(EINVAL);
}
Errno r;
int iexp;
if(x<0) {
x=-x;
m_neg=true;
} else {
m_neg=false;
}
x=Wy::frexp(x,&iexp);
x=Wy::ldexp(x,Limits<FType>::Bits);
m_exp=iexp-Limits<FType>::Bits;
if((r=m_mant.set_num(MantType::itv(static_cast<UIntMant>(x))))!=Ok) {
throw r;
}
if((r=_finalize())!=Ok) {
throw r;
}
}
catch(const Errno& e) {
WY_THROW( Reply(e) );
};
--
Most of the time while asking questions in comp.lang.c/c++, I need to rewrite a bit.
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