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| From | Keith Thompson <kst-u@mib.org> |
|---|---|
| Newsgroups | comp.lang.c |
| Subject | Re: Register storage type |
| Date | 2011-05-12 14:27 -0700 |
| Organization | None to speak of |
| Message-ID | <lnaaerk3sg.fsf@nuthaus.mib.org> (permalink) |
| References | <iqhhgg$d8j$1@speranza.aioe.org> <OeGdnRorOK1J11HQnZ2dnUVZ_gSdnZ2d@bestweb.net> <iqhiie$g5j$1@speranza.aioe.org> |
Free Willy <nospam@nospam.com> writes:
> Kenneth Brody writes:
>> On 5/12/2011 4:55 PM, Free Willy wrote:
>>> Say the CPU has only AL, BL, CL, DL or eight 8 bit registers, and if
>>> want to declare 10 register variables in my code, is it possible to do
>>> it?
>>>
>>> Say size_of(float) is the same as size_of(int), is it possible to
>>> define a "register float" variable? How will the register get converted
>>> between int and float?
>>
>> The "register" keyword is just a hint to the compiler, which it is free
>> to use or ignore as it sees fit.
>
> OK, but will it always give a warning if you try to assign too many
> register variables for the CPU (or the wrong type of variable, if this
> isn't supported), or just compile it possibly with errors or undefined
> behaviors at runtime?
A compiler can warn about anything it likes, and some might give such a
warning, either by default or by the use of some command-line option.
But no such warning is required, and as far as I know most compilers
won't bother.
Declaring "too many" register variables won't cause errors or undefined
behavior. The compiler isn't disobeying the "register" specifier, since
the specifier (in spite of the name) doesn't say to store the variable
in a register.
> Another question is array variables declared as register type - could the
> compiler put a small array say of 3 elements into different registers and
> translate array accesses to the right register?
If you declare an array variable as "register", you can't take its
address. Since array indexing is defined in terms of addresses, such an
array variable is pretty much useless.
If you declare an array variable *without* "register", the compiler can
store it in one or more registers, as long as the behavior of the
program is not affected. For example, if you take the address of one of
the elements of the array and pass it to some function, the compiler
isn't likely to be able to store it in a register, since the called
function woudnl't know how to access it.
--
Keith Thompson (The_Other_Keith) kst-u@mib.org <http://www.ghoti.net/~kst>
Nokia
"We must do something. This is something. Therefore, we must do this."
-- Antony Jay and Jonathan Lynn, "Yes Minister"
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Register storage type Free Willy <nospam@nospam.com> - 2011-05-12 20:55 +0000
Re: Register storage type Kenneth Brody <kenbrody@spamcop.net> - 2011-05-12 17:02 -0400
Re: Register storage type Free Willy <nospam@nospam.com> - 2011-05-12 21:13 +0000
Re: Register storage type Angel <angel+news@spamcop.net> - 2011-05-12 21:20 +0000
Re: Register storage type Keith Thompson <kst-u@mib.org> - 2011-05-12 14:27 -0700
Re: Register storage type Kenneth Brody <kenbrody@spamcop.net> - 2011-05-13 13:20 -0400
Re: Register storage type Free Willy <nospam@nospam.com> - 2011-05-13 21:30 +0000
Re: Register storage type Keith Thompson <kst-u@mib.org> - 2011-05-13 15:50 -0700
Different languages (Was: Register storage type) gazelle@shell.xmission.com (Kenny McCormack) - 2011-05-14 08:58 +0000
Re: Different languages (Was: Register storage type) Dr Nick <3-nospam@temporary-address.org.uk> - 2011-05-14 10:09 +0100
Re: Register storage type Free Willy <nospam@nospam.com> - 2011-05-14 21:27 +0000
Re: Register storage type Ian Collins <ian-news@hotmail.com> - 2011-05-15 09:55 +1200
Re: Register storage type Keith Thompson <kst-u@mib.org> - 2011-05-14 16:46 -0700
Re: Register storage type Jens <jens.gustedt@gmail.com> - 2011-05-15 10:08 -0700
Re: Register storage type James Kuyper <jameskuyper@verizon.net> - 2011-05-15 14:09 -0400
Re: Register storage type David Thompson <dave.thompson2@verizon.net> - 2011-05-19 01:50 -0400
Re: Register storage type Stephen Sprunk <stephen@sprunk.org> - 2011-05-15 00:27 -0500
Re: Register storage type Angel <angel+news@spamcop.net> - 2011-05-15 12:56 +0000
Re: Register storage type Eric Sosman <esosman@ieee-dot-org.invalid> - 2011-05-15 11:54 -0400
Re: Register storage type Seebs <usenet-nospam@seebs.net> - 2011-05-15 17:43 +0000
Re: Register storage type Tim Rentsch <txr@alumni.caltech.edu> - 2011-05-18 23:37 -0700
Re: Register storage type Seebs <usenet-nospam@seebs.net> - 2011-05-19 14:37 +0000
Drift: Linguistics (was Re: Register storage type) Kenneth Brody <kenbrody@spamcop.net> - 2011-05-19 13:17 -0400
Re: Register storage type Tim Rentsch <txr@alumni.caltech.edu> - 2011-05-19 11:05 -0700
Re: Register storage type Seebs <usenet-nospam@seebs.net> - 2011-05-19 19:08 +0000
Re: Register storage type Tim Rentsch <txr@alumni.caltech.edu> - 2011-05-24 00:39 -0700
Re: Register storage type Ian Collins <ian-news@hotmail.com> - 2011-05-20 07:46 +1200
Re: Register storage type Eric Sosman <esosman@ieee-dot-org.invalid> - 2011-05-19 22:37 -0400
Re: Register storage type Michael Press <rubrum@pacbell.net> - 2011-05-25 12:57 -0700
Re: Register storage type pete <pfiland@mindspring.com> - 2011-05-15 09:09 -0400
Re: Register storage type Eric Sosman <esosman@ieee-dot-org.invalid> - 2011-05-12 21:57 -0400
Re: Register storage type Angel <angel+news@spamcop.net> - 2011-05-12 21:14 +0000
Re: Register storage type gordonb.unc3q@burditt.org (Gordon Burditt) - 2011-05-13 07:49 -0500
Re: Register storage type Keith Thompson <kst-u@mib.org> - 2011-05-12 14:20 -0700
Re: Register storage type Seebs <usenet-nospam@seebs.net> - 2011-05-12 21:59 +0000
Re: Register storage type BGB <cr88192@hotmail.com> - 2011-05-12 15:50 -0700
Re: Register storage type Keith Thompson <kst-u@mib.org> - 2011-05-12 15:49 -0700
Re: Register storage type Seebs <usenet-nospam@seebs.net> - 2011-05-12 23:19 +0000
Re: Register storage type Keith Thompson <kst-u@mib.org> - 2011-05-12 16:29 -0700
Re: Register storage type Seebs <usenet-nospam@seebs.net> - 2011-05-13 00:15 +0000
Re: Register storage type Columbus sailed the ocean China Blue <chine.bleu@yahoo.com> - 2011-05-12 15:24 -0700
Re: Register storage type Peter Nilsson <airia@acay.com.au> - 2011-05-12 17:39 -0700
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