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Groups > comp.lang.c++ > #81866
| From | Bart <bc@freeuk.com> |
|---|---|
| Newsgroups | comp.lang.c++ |
| Subject | Re: How to get mantissa of long double? |
| Date | 2021-10-05 19:21 +0100 |
| Organization | A noiseless patient Spider |
| Message-ID | <sji534$v2o$1@dont-email.me> (permalink) |
| References | (10 earlier) <sjffn2$7dq$1@dont-email.me> <sjgmsn$4nr$2@dont-email.me> <sjgvvg$pnt$1@dont-email.me> <87r1cz8nlm.fsf@nosuchdomain.example.com> <sji157$u7b$2@dont-email.me> |
On 05/10/2021 18:14, Bonita Montero wrote:
> Am 05.10.2021 um 18:04 schrieb Keith Thompson:
>> David Brown <david.brown@hesbynett.no> writes:
>>> On 05/10/2021 07:12, Bonita Montero wrote:
>>>> Am 04.10.2021 um 20:04 schrieb David Brown:
>>>>
>>>>> MSVC for ARM has 64-bit "long doubles" even on 64-bit ARM, other
>>>>> 64-bit
>>>>> ARM targets have 128-bit (I don't know off-hand if they are IEEE quad
>>>>> precision). For RISC-V, even 32-bit targets have 128-bit "long
>>>>> double".
>>>>
>>>> There isn't any ARM-implementation with 128 bit FP.
>>>
>>> And you know that because ... what? Because you are confusing hardware
>>> floating point with floating point in general?
>>
>> $ uname -m
>> aarch64
>> $ cat c.c
>> #include <stdio.h>
>> #include <limits.h>
>> #include <float.h>
>>
>> int main(void) {
>> printf("sizeof (long double) = %zu (%zu bits), LDBL_DIG = %d\n",
>> sizeof (long double),
>> CHAR_BIT * sizeof (long double),
>> LDBL_DIG);
>> }
>> $ gcc c.c -o c && ./c
>> sizeof (long double) = 16 (128 bits), LDBL_DIG = 33
>> $
>
> That's pure software - your CPU doesn't natively support 128 bit FP.
>
Does it matter?
Suppose there /is/ a long double type which is wider than double,
however many bits it is, or whether it's implemented in hardware or
software: how do you then extract its mantissa?
I showed a non-portable way of doing when it was Intel's 80-bit type. My
method used x87 instructions, but it's actually even simpler without it:
just take the first 64 bits of the 80-bit little-endian representation.
(That only works with that 80-bit format.)
But for anything beyond 80 bits, or for something that works on any size
of float, you will need a different approach, and possibly a uint128 type.
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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
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