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| From | Keith Thompson <kst-u@mib.org> |
|---|---|
| Newsgroups | comp.lang.c |
| Subject | Re: Is uint32_t foo(uint32_t x) { return (uint32_t)(x*x); } portable? |
| Date | 2016-11-28 23:37 -0800 |
| Organization | None to speak of |
| Message-ID | <ln4m2qag9n.fsf@kst-u.example.com> (permalink) |
| References | (3 earlier) <o192rl$tok$1@dont-email.me> <871sxz7qzw.fsf@bsb.me.uk> <e6af8d35-de73-4893-ace7-eb617a805475@googlegroups.com> <lnfumfb9p0.fsf@kst-u.example.com> <c808ca65-c717-4c0f-96c2-2e84911e5195@googlegroups.com> |
supercat@casperkitty.com writes:
> On Friday, November 25, 2016 at 2:11:17 PM UTC-6, Keith Thompson wrote:
>> supercat writes:
>> > Implementations where every unsigned value is representable as "int" are
>> > hardly pathological.
>>
>> I won't argue the meaning of the word "pathological", but such
>> implementations are certainly rare.
>
> I certainly won't dispute that.
>
>> > That would actually be a common state of affairs in
>> > sign-magnitude or ones'-complement implementations.
>>
>> I've never used a sign-and-magnitude or ones'-complement implementation,
>> but I'd expect such an implementation to use all the bits of a word for
>> both signed and unsigned types. For example, if int and unsigned int
>> are, say, 16 bits wide, I'd expect that most likely int would have a
>> range of -32767..+32767, and unsigned int to have a range of 0..65535.
>> Certainly there are other possibilities, including ones where the range
>> of unsigned int matches the non-negative subrange of int, but I'd expect
>> that to be unusual, perhaps even nonexistent.
>>
>> Do you have a concrete example, or are you just speculating?
>
> http://public.support.unisys.com/2200/docs/cp14.0/pdf/78310422-011.pdf
Thank you for posting that.
> I don't know exactly how such hardware works, but I would expect that since
> the compiler achieves conformance by looping off a bit, that would imply that
> having an unsigned type support all 36 bits would be difficult.
(The link is to a download page, not to the actual PDF.)
I think you've misread it.
(Not relevant to the point, but section 4.3 treats "plain integers" and
"signed integers" as distinct, which is nonsense.)
For example, int and unsigned int are both 36 bits. The range of int is
shown as -2**35+1 to +2**35-1, and range of unsigned int as 0 to
2**36-2. (There's a conformance option that makes the upper bound of
unsigned int 2**36-1.)
It doesn't lop off a bit for unsigned types, it lops of a single value.
(I don't know why, but I haven't given it much thought.)
[...]
--
Keith Thompson (The_Other_Keith) kst-u@mib.org <http://www.ghoti.net/~kst>
Working, but not speaking, for JetHead Development, Inc.
"We must do something. This is something. Therefore, we must do this."
-- Antony Jay and Jonathan Lynn, "Yes Minister"
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Is uint32_t foo(uint32_t x) { return (uint32_t)(x*x); } portable? Francois Grieu <fgrieu@free.fr> - 2016-11-24 15:33 +0100
Re: Is uint32_t foo(uint32_t x) { return (uint32_t)(x*x); } portable? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2016-11-24 14:59 +0000
Re: Is uint32_t foo(uint32_t x) { return (uint32_t)(x*x); } portable? Francois Grieu <fgrieu@free.fr> - 2016-11-24 18:34 +0100
Re: Is uint32_t foo(uint32_t x) { return (uint32_t)(x*x); } portable? supercat@casperkitty.com - 2016-11-24 14:03 -0800
Re: Is uint32_t foo(uint32_t x) { return (uint32_t)(x*x); } portable? David Brown <david.brown@hesbynett.no> - 2016-11-25 09:50 +0100
Re: Is uint32_t foo(uint32_t x) { return (uint32_t)(x*x); } portable? Noob <root@127.0.0.1> - 2016-11-25 09:44 +0100
Re: Is uint32_t foo(uint32_t x) { return (uint32_t)(x*x); } portable? David Brown <david.brown@hesbynett.no> - 2016-11-25 11:14 +0100
Re: Is uint32_t foo(uint32_t x) { return (uint32_t)(x*x); } portable? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2016-11-25 11:12 +0000
Re: Is uint32_t foo(uint32_t x) { return (uint32_t)(x*x); } portable? supercat@casperkitty.com - 2016-11-25 10:50 -0800
Re: Is uint32_t foo(uint32_t x) { return (uint32_t)(x*x); } portable? Keith Thompson <kst-u@mib.org> - 2016-11-25 12:12 -0800
Re: Is uint32_t foo(uint32_t x) { return (uint32_t)(x*x); } portable? Nick Bowler <nbowler@draconx.ca> - 2016-11-25 21:45 +0000
Re: Is uint32_t foo(uint32_t x) { return (uint32_t)(x*x); } portable? supercat@casperkitty.com - 2016-11-25 13:58 -0800
Re: Is uint32_t foo(uint32_t x) { return (uint32_t)(x*x); } portable? Keith Thompson <kst-u@mib.org> - 2016-11-28 23:37 -0800
Re: Is uint32_t foo(uint32_t x) { return (uint32_t)(x*x); } portable? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2016-11-29 12:01 +0000
Re: Is uint32_t foo(uint32_t x) { return (uint32_t)(x*x); } portable? supercat@casperkitty.com - 2016-11-29 07:39 -0800
Re: Is uint32_t foo(uint32_t x) { return (uint32_t)(x*x); } portable? Keith Thompson <kst-u@mib.org> - 2016-11-29 09:12 -0800
Re: Is uint32_t foo(uint32_t x) { return (uint32_t)(x*x); } portable? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2016-11-25 22:54 +0000
Re: Is uint32_t foo(uint32_t x) { return (uint32_t)(x*x); } portable? Nick Bowler <nbowler@draconx.ca> - 2016-11-25 22:01 +0000
Re: Is uint32_t foo(uint32_t x) { return (uint32_t)(x*x); } portable? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2016-11-25 23:22 +0000
Re: Is uint32_t foo(uint32_t x) { return (uint32_t)(x*x); } portable? Tim Rentsch <txr@alumni.caltech.edu> - 2016-12-10 07:22 -0800
Re: Is uint32_t foo(uint32_t x) { return (uint32_t)(x*x); } portable? Tim Rentsch <txr@alumni.caltech.edu> - 2016-12-01 10:16 -0800
Re: Is uint32_t foo(uint32_t x) { return (uint32_t)(x*x); } portable? Barry Schwarz <schwarzb@dqel.com> - 2016-12-01 11:06 -0800
Re: Is uint32_t foo(uint32_t x) { return (uint32_t)(x*x); } portable? supercat@casperkitty.com - 2016-12-01 12:40 -0800
Re: Is uint32_t foo(uint32_t x) { return (uint32_t)(x*x); } portable? David Brown <david.brown@hesbynett.no> - 2016-12-02 09:28 +0100
Re: Is uint32_t foo(uint32_t x) { return (uint32_t)(x*x); } portable? Tim Rentsch <txr@alumni.caltech.edu> - 2016-12-10 07:13 -0800
Re: Is uint32_t foo(uint32_t x) { return (uint32_t)(x*x); } portable? supercat@casperkitty.com - 2016-12-10 10:41 -0800
Re: Is uint32_t foo(uint32_t x) { return (uint32_t)(x*x); } portable? supercat@casperkitty.com - 2016-11-24 07:40 -0800
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