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Groups > comp.lang.c > #29128 > unrolled thread
| Started by | Edward Rutherford <edward.p.rutherford79@REMOVETHIS.gmail.com> |
|---|---|
| First post | 2012-12-10 17:14 +0000 |
| Last post | 2012-12-10 20:20 -0500 |
| Articles | 19 on this page of 99 — 21 participants |
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Pointer Arithmetic & UB Edward Rutherford <edward.p.rutherford79@REMOVETHIS.gmail.com> - 2012-12-10 17:14 +0000
Re: Pointer Arithmetic & UB "christian.bau" <christian.bau@cbau.wanadoo.co.uk> - 2012-12-10 09:35 -0800
Re: Pointer Arithmetic & UB James Kuyper <jameskuyper@verizon.net> - 2012-12-10 12:55 -0500
Re: Pointer Arithmetic & UB Eric Sosman <esosman@comcast-dot-net.invalid> - 2012-12-10 13:25 -0500
Re: Pointer Arithmetic & UB falk@rahul.net (Edward A. Falk) - 2012-12-11 00:46 +0000
Re: Pointer Arithmetic & UB James Kuyper <jameskuyper@verizon.net> - 2012-12-10 21:28 -0500
Re: Pointer Arithmetic & UB Ken Brody <kenbrody@spamcop.net> - 2012-12-12 14:36 -0500
Re: Pointer Arithmetic & UB glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2012-12-12 20:35 +0000
Re: Pointer Arithmetic & UB James Kuyper <jameskuyper@verizon.net> - 2012-12-12 15:57 -0500
Re: Pointer Arithmetic & UB Eric Sosman <esosman@comcast-dot-net.invalid> - 2012-12-12 16:02 -0500
Re: Pointer Arithmetic & UB James Kuyper <jameskuyper@verizon.net> - 2012-12-12 16:13 -0500
Re: Pointer Arithmetic & UB Eric Sosman <esosman@comcast-dot-net.invalid> - 2012-12-12 21:18 -0500
Re: Pointer Arithmetic & UB James Kuyper <jameskuyper@verizon.net> - 2012-12-12 22:42 -0500
Re: Pointer Arithmetic & UB Phil Carmody <thefatphil_demunged@yahoo.co.uk> - 2012-12-17 12:04 +0200
Re: Pointer Arithmetic & UB Eric Sosman <esosman@comcast-dot-net.invalid> - 2012-12-17 08:47 -0500
Re: Pointer Arithmetic & UB Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-12-17 14:58 +0000
Re: Pointer Arithmetic & UB Eric Sosman <esosman@comcast-dot-net.invalid> - 2012-12-17 10:59 -0500
Re: Pointer Arithmetic & UB Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-12-17 17:26 +0000
Re: Pointer Arithmetic & UB Shao Miller <sha0.miller@gmail.com> - 2012-12-17 19:33 -0500
Re: Pointer Arithmetic & UB Ken Brody <kenbrody@spamcop.net> - 2012-12-20 11:00 -0500
Re: Pointer Arithmetic & UB Tim Rentsch <txr@alumni.caltech.edu> - 2012-12-20 10:03 -0800
Re: Pointer Arithmetic & UB Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-12-20 22:02 +0000
Re: Pointer Arithmetic & UB Tim Rentsch <txr@alumni.caltech.edu> - 2012-12-21 13:09 -0800
Re: Pointer Arithmetic & UB glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2012-12-21 22:40 +0000
Re: Pointer Arithmetic & UB Ken Brody <kenbrody@spamcop.net> - 2012-12-21 23:39 -0500
Re: Pointer Arithmetic & UB glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2012-12-22 06:50 +0000
Re: Pointer Arithmetic & UB Tim Rentsch <txr@alumni.caltech.edu> - 2012-12-22 00:15 -0800
Re: Pointer Arithmetic & UB glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2012-12-22 10:34 +0000
Re: Pointer Arithmetic & UB Tim Rentsch <txr@alumni.caltech.edu> - 2012-12-22 09:32 -0800
Re: Pointer Arithmetic & UB glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2012-12-23 09:38 +0000
Re: Pointer Arithmetic & UB Tim Rentsch <txr@alumni.caltech.edu> - 2012-12-23 09:55 -0800
Re: Pointer Arithmetic & UB Ken Brody <kenbrody@spamcop.net> - 2012-12-26 13:35 -0500
Re: Pointer Arithmetic & UB Tim Rentsch <txr@alumni.caltech.edu> - 2012-12-27 09:03 -0800
Re: Pointer Arithmetic & UB Ken Brody <kenbrody@spamcop.net> - 2012-12-27 21:31 -0500
Re: Pointer Arithmetic & UB Philip Lantz <prl@canterey.us> - 2012-12-28 01:55 -0800
Re: Pointer Arithmetic & UB Tim Rentsch <txr@alumni.caltech.edu> - 2012-12-29 13:43 -0800
Re: Pointer Arithmetic & UB Philip Lantz <prl@canterey.us> - 2012-12-28 01:39 -0800
Re: Pointer Arithmetic & UB glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2012-12-28 11:31 +0000
Re: Pointer Arithmetic & UB Keith Thompson <kst-u@mib.org> - 2012-12-28 08:47 -0800
Re: Pointer Arithmetic & UB Tim Rentsch <txr@alumni.caltech.edu> - 2012-12-29 17:45 -0800
Re: Pointer Arithmetic & UB glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2012-12-30 04:06 +0000
Re: Pointer Arithmetic & UB Tim Rentsch <txr@alumni.caltech.edu> - 2013-01-02 10:08 -0800
Re: Pointer Arithmetic & UB Ken Brody <kenbrody@spamcop.net> - 2012-12-26 13:29 -0500
Re: Pointer Arithmetic & UB Tim Rentsch <txr@alumni.caltech.edu> - 2012-12-27 07:55 -0800
Re: Pointer Arithmetic & UB Tim Rentsch <txr@alumni.caltech.edu> - 2012-12-27 08:01 -0800
Re: Pointer Arithmetic & UB Ken Brody <kenbrody@spamcop.net> - 2012-12-27 21:10 -0500
Re: Pointer Arithmetic & UB Tim Rentsch <txr@alumni.caltech.edu> - 2012-12-29 18:03 -0800
Re: Pointer Arithmetic & UB Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-12-23 03:48 +0000
Re: Pointer Arithmetic & UB Tim Rentsch <txr@alumni.caltech.edu> - 2012-12-23 10:22 -0800
Re: Pointer Arithmetic & UB Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-12-27 10:34 +0000
Re: Pointer Arithmetic & UB Tim Rentsch <txr@alumni.caltech.edu> - 2012-12-27 10:16 -0800
Re: Pointer Arithmetic & UB Ben Bacarisse <ben.usenet@bsb.me.uk> - 2013-01-10 17:26 +0000
Re: Pointer Arithmetic & UB Robert Wessel <robertwessel2@yahoo.com> - 2012-12-20 12:21 -0600
Re: Pointer Arithmetic & UB James Kuyper <jameskuyper@verizon.net> - 2012-12-20 13:40 -0500
Re: Pointer Arithmetic & UB Robert Wessel <robertwessel2@yahoo.com> - 2012-12-20 13:32 -0600
Re: Pointer Arithmetic & UB James Kuyper <jameskuyper@verizon.net> - 2012-12-20 14:58 -0500
Re: Pointer Arithmetic & UB glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2012-12-20 21:54 +0000
Re: Pointer Arithmetic & UB Lanarcam <lanarcam1@yahoo.fr> - 2012-12-20 19:49 +0100
Re: Pointer Arithmetic & UB Phil Carmody <thefatphil_demunged@yahoo.co.uk> - 2012-12-21 02:38 +0200
Re: Pointer Arithmetic & UB Ken Brody <kenbrody@spamcop.net> - 2012-12-21 14:33 -0500
Re: Pointer Arithmetic & UB Shao Miller <sha0.miller@gmail.com> - 2012-12-21 03:18 -0500
Re: Pointer Arithmetic & UB Tim Rentsch <txr@alumni.caltech.edu> - 2012-12-21 13:16 -0800
Re: Pointer Arithmetic & UB Shao Miller <sha0.miller@gmail.com> - 2012-12-21 17:57 -0500
Re: Pointer Arithmetic & UB glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2012-12-21 23:52 +0000
Re: Pointer Arithmetic & UB Shao Miller <sha0.miller@gmail.com> - 2012-12-21 19:47 -0500
Re: Pointer Arithmetic & UB Tim Rentsch <txr@alumni.caltech.edu> - 2012-12-21 22:54 -0800
Re: Pointer Arithmetic & UB Shao Miller <sha0.miller@gmail.com> - 2012-12-22 03:31 -0500
Re: Pointer Arithmetic & UB Tim Rentsch <txr@alumni.caltech.edu> - 2012-12-22 09:16 -0800
Re: Pointer Arithmetic & UB Shao Miller <sha0.miller@gmail.com> - 2012-12-24 04:23 -0500
Re: Pointer Arithmetic & UB Tim Rentsch <txr@alumni.caltech.edu> - 2012-12-27 11:07 -0800
Re: Pointer Arithmetic & UB Tim Rentsch <txr@alumni.caltech.edu> - 2012-12-17 02:33 -0800
Re: Pointer Arithmetic & UB Tim Rentsch <txr@alumni.caltech.edu> - 2012-12-17 02:18 -0800
Re: Pointer Arithmetic & UB Noob <root@127.0.0.1> - 2012-12-11 11:36 +0100
Re: Pointer Arithmetic & UB "christian.bau" <christian.bau@cbau.wanadoo.co.uk> - 2012-12-11 10:00 -0800
Re: Pointer Arithmetic & UB Phil Carmody <thefatphil_demunged@yahoo.co.uk> - 2012-12-17 12:11 +0200
Re: Pointer Arithmetic & UB Eric Sosman <esosman@comcast-dot-net.invalid> - 2012-12-11 15:27 -0500
Re: Pointer Arithmetic & UB glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2012-12-11 21:09 +0000
Re: Pointer Arithmetic & UB Ken Brody <kenbrody@spamcop.net> - 2012-12-12 14:30 -0500
Re: Pointer Arithmetic & UB Keith Thompson <kst-u@mib.org> - 2012-12-12 11:42 -0800
Re: Pointer Arithmetic & UB Ken Brody <kenbrody@spamcop.net> - 2012-12-12 17:12 -0500
Re: Pointer Arithmetic & UB Phil Carmody <thefatphil_demunged@yahoo.co.uk> - 2012-12-17 12:16 +0200
Re: Pointer Arithmetic & UB Prathamesh Kulkarni <bilbotheelffriend@gmail.com> - 2012-12-10 12:04 -0800
Re: Pointer Arithmetic & UB James Kuyper <jameskuyper@verizon.net> - 2012-12-10 15:29 -0500
Re: Pointer Arithmetic & UB Prathamesh Kulkarni <bilbotheelffriend@gmail.com> - 2012-12-10 12:44 -0800
Re: Pointer Arithmetic & UB Prathamesh Kulkarni <bilbotheelffriend@gmail.com> - 2012-12-10 12:47 -0800
Re: Pointer Arithmetic & UB James Kuyper <jameskuyper@verizon.net> - 2012-12-10 16:02 -0500
Re: Pointer Arithmetic & UB Prathamesh Kulkarni <bilbotheelffriend@gmail.com> - 2012-12-10 13:08 -0800
Re: Pointer Arithmetic & UB Ken Brody <kenbrody@spamcop.net> - 2012-12-12 14:26 -0500
Re: Pointer Arithmetic & UB Greg Martin <greg@softsprocket.com> - 2012-12-10 14:55 -0800
Re: Pointer Arithmetic & UB Sjouke Burry <s@b> - 2012-12-10 21:18 +0000
Re: Pointer Arithmetic & UB falk@rahul.net (Edward A. Falk) - 2012-12-11 00:48 +0000
Re: Pointer Arithmetic & UB glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2012-12-10 21:01 +0000
Re: Pointer Arithmetic & UB Ken Brody <kenbrody@spamcop.net> - 2012-12-12 14:24 -0500
Re: Pointer Arithmetic & UB Robert Wessel <robertwessel2@yahoo.com> - 2012-12-12 14:34 -0600
Re: Pointer Arithmetic & UB glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2012-12-12 20:45 +0000
Re: Pointer Arithmetic & UB Robert Wessel <robertwessel2@yahoo.com> - 2012-12-12 15:29 -0600
Re: Pointer Arithmetic & UB glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2012-12-13 02:02 +0000
Re: Pointer Arithmetic & UB Malcolm McLean <malcolm.mclean5@btinternet.com> - 2012-12-17 05:57 -0800
Re: Pointer Arithmetic & UB pete <pfiland@mindspring.com> - 2012-12-10 20:20 -0500
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| From | Phil Carmody <thefatphil_demunged@yahoo.co.uk> |
|---|---|
| Date | 2012-12-17 12:16 +0200 |
| Message-ID | <87txrlj85n.fsf@bazspaz.fatphil.org> |
| In reply to | #29175 |
Ken Brody <kenbrody@spamcop.net> writes: > On 12/10/2012 7:46 PM, Edward A. Falk wrote: > > In article <ka59e6$mq7$1@dont-email.me>, > > Eric Sosman <esosman@comcast-dot-net.invalid> wrote: > >> > >> A colleague who did some work on IBM's AS/400 (they've > >> changed the name; I forget the new one) told me that simply > >> trying to calculate an out-of-range pointer yielded a null > >> pointer as a result. > > > > Heh; learn something new every day. I never would have guessed > > that there was an actual architecture that would blow up with > > this construct. > > > > I assume that *(a+(i-j)) would be ok? > > No. There is no requirement that the value of "i-j" be calculated > prior to adding it to "a". (Check the numerous threads here involving > using parentheses to "fix" UB in things involving such constructs as > "i + (i++)".) Operator precedence only guarantees how the expression > is to be interpreted, not the actual order of evaluation. The "*(a+(i-j))" expression has *nothing* in common with the part of the "i+(i++)" that pertains to UB. That brackets fail to do something in an unrelated situation is basically irrelevant. Phil -- I'm not saying that google groups censors my posts, but there's a strong link between me saying "google groups sucks" in articles, and them disappearing. Oh - I guess I might be saying that google groups censors my posts.
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| From | Prathamesh Kulkarni <bilbotheelffriend@gmail.com> |
|---|---|
| Date | 2012-12-10 12:04 -0800 |
| Message-ID | <e4659f49-c39e-4367-bbad-c2724a3ebd13@googlegroups.com> |
| In reply to | #29128 |
Instead, of i and j would *(a + 20 - 15) still have undefined behaviour ? Probably any C compiler will evaluate 20 - 15 during translation, but does the standard require constant expression to be evaluated during translation even if it is a sub-expression as in the above case ? Thanks ;)
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| From | James Kuyper <jameskuyper@verizon.net> |
|---|---|
| Date | 2012-12-10 15:29 -0500 |
| Message-ID | <50C6461E.40208@verizon.net> |
| In reply to | #29134 |
On 12/10/2012 03:04 PM, Prathamesh Kulkarni wrote: > Instead, of i and j > would *(a + 20 - 15) still have > undefined behaviour ? Probably any C compiler > will evaluate 20 - 15 during translation, but > does the standard require constant expression > to be evaluated during translation > even if it is a sub-expression > as in the above case ? No, it does not. It would be an unusual compiler that failed to do so, but it is not required.
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| From | Prathamesh Kulkarni <bilbotheelffriend@gmail.com> |
|---|---|
| Date | 2012-12-10 12:44 -0800 |
| Message-ID | <232fe1b0-d8fa-42e2-85d8-12bcba97a4a1@googlegroups.com> |
| In reply to | #29136 |
On Monday, 10 December 2012 15:29:18 UTC-5, James Kuyper wrote: > On 12/10/2012 03:04 PM, Prathamesh Kulkarni wrote: > > > Instead, of i and j > > > would *(a + 20 - 15) still have > > > undefined behaviour ? Probably any C compiler > > > will evaluate 20 - 15 during translation, but > > > does the standard require constant expression > > > to be evaluated during translation > > > even if it is a sub-expression > > > as in the above case ? > > > > No, it does not. It would be an unusual compiler that failed to do so, > > but it is not required. Yes, I got that, that's why I deleted my post immediately after posting. How were you able to see it ? How
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| From | Prathamesh Kulkarni <bilbotheelffriend@gmail.com> |
|---|---|
| Date | 2012-12-10 12:47 -0800 |
| Message-ID | <f954578b-8c15-44ee-9f34-0fb2bf90af61@googlegroups.com> |
| In reply to | #29137 |
On Monday, 10 December 2012 15:44:37 UTC-5, Prathamesh Kulkarni wrote: > On Monday, 10 December 2012 15:29:18 UTC-5, James Kuyper wrote: > > > On 12/10/2012 03:04 PM, Prathamesh Kulkarni wrote: > > > > > > > Instead, of i and j > > > > > > > would *(a + 20 - 15) still have > > > > > > > undefined behaviour ? Probably any C compiler > > > > > > > will evaluate 20 - 15 during translation, but > > > > > > > does the standard require constant expression > > > > > > > to be evaluated during translation > > > > > > > even if it is a sub-expression > > > > > > > as in the above case ? > > > > > > > > > > > > No, it does not. It would be an unusual compiler that failed to do so, > > > > > > but it is not required. > > > > Yes, I got that, that's why I deleted my post immediately > > after posting. How were you able to see it ? > > How It repeated the word "How" ;) Is there some problem with the google interface ?
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| From | James Kuyper <jameskuyper@verizon.net> |
|---|---|
| Date | 2012-12-10 16:02 -0500 |
| Message-ID | <50C64DEF.2050506@verizon.net> |
| In reply to | #29138 |
On 12/10/2012 03:47 PM, Prathamesh Kulkarni wrote: ... >> Yes, I got that, that's why I deleted my post immediately Forged cancellation notices used to be common; as a result, most news servers now ignore cancellation requests that come from other news servers. Your request presumably deleted the message from Google's archive, which is one of the largest and most widely used on the planet - but it probably didn't delete many of the thousands of other copies stored stored in various places around the world. >> after posting. How were you able to see it ? >> >> How > > It repeated the word "How" ;) > Is there some problem with the google interface ? That's sort of like asking if the sea is wet. I recommend getting better news server (I can strongly recommend eternalseptember.org, which is free) and a monitoring it using decent newsreader (my favorite is Mozilla thunderbird, but many people prefer other news readers).
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| From | Prathamesh Kulkarni <bilbotheelffriend@gmail.com> |
|---|---|
| Date | 2012-12-10 13:08 -0800 |
| Message-ID | <2a27f6cf-5f1f-45f8-8925-d27b56b06b7a@googlegroups.com> |
| In reply to | #29140 |
On Monday, 10 December 2012 16:02:39 UTC-5, James Kuyper wrote: > On 12/10/2012 03:47 PM, Prathamesh Kulkarni wrote: > > ... > > >> Yes, I got that, that's why I deleted my post immediately > > > > Forged cancellation notices used to be common; as a result, most news > > servers now ignore cancellation requests that come from other news > > servers. Your request presumably deleted the message from Google's > > archive, which is one of the largest and most widely used on the planet > > - but it probably didn't delete many of the thousands of other copies > > stored stored in various places around the world. > > > > >> after posting. How were you able to see it ? > > >> > > >> How > > > > > > It repeated the word "How" ;) > > > Is there some problem with the google interface ? > > > > That's sort of like asking if the sea is wet. I recommend getting better > > news server (I can strongly recommend eternalseptember.org, which is > > free) and a monitoring it using decent newsreader (my favorite is > > Mozilla thunderbird, but many people prefer other news readers). Thanks, I will give a try to eternalseptember.org,
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| From | Ken Brody <kenbrody@spamcop.net> |
|---|---|
| Date | 2012-12-12 14:26 -0500 |
| Message-ID | <kaalpm$3uf$2@dont-email.me> |
| In reply to | #29141 |
On 12/10/2012 4:08 PM, Prathamesh Kulkarni wrote:
> On Monday, 10 December 2012 16:02:39 UTC-5, James Kuyper wrote:
>> On 12/10/2012 03:47 PM, Prathamesh Kulkarni wrote:
[...]
>>> Is there some problem with the google interface ?
>>
>>
>>
>> That's sort of like asking if the sea is wet. I recommend getting better
>> news server (I can strongly recommend eternalseptember.org, which is
>> free) and a monitoring it using decent newsreader (my favorite is
>> Mozilla thunderbird, but many people prefer other news readers).
>
> Thanks, I will give a try to eternalseptember.org,
There's a hyphen there:
eternal-september.org
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| From | Greg Martin <greg@softsprocket.com> |
|---|---|
| Date | 2012-12-10 14:55 -0800 |
| Message-ID | <vLtxs.10170$eK6.8648@newsfe31.iad> |
| In reply to | #29140 |
On 12-12-10 01:02 PM, James Kuyper wrote: > On 12/10/2012 03:47 PM, Prathamesh Kulkarni wrote: > ... >>> Yes, I got that, that's why I deleted my post immediately > > Forged cancellation notices used to be common; as a result, most news > servers now ignore cancellation requests that come from other news > servers. Your request presumably deleted the message from Google's > archive, which is one of the largest and most widely used on the planet > - but it probably didn't delete many of the thousands of other copies > stored stored in various places around the world. > >>> after posting. How were you able to see it ? >>> >>> How >> >> It repeated the word "How" ;) >> Is there some problem with the google interface ? > > That's sort of like asking if the sea is wet. I recommend getting better > news server (I can strongly recommend eternalseptember.org, which is > free) and a monitoring it using decent newsreader (my favorite is > Mozilla thunderbird, but many people prefer other news readers). > I think that should be eternal-september.org.
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| From | Sjouke Burry <s@b> |
|---|---|
| Date | 2012-12-10 21:18 +0000 |
| Message-ID | <XnsA125DE858696Bsjoukeburrysoesterbe@213.75.12.10> |
| In reply to | #29137 |
Prathamesh Kulkarni <bilbotheelffriend@gmail.com> wrote in news:232fe1b0- d8fa-42e2-85d8-12bcba97a4a1@googlegroups.com: > On Monday, 10 December 2012 15:29:18 UTC-5, James Kuyper wrote: >> On 12/10/2012 03:04 PM, Prathamesh Kulkarni wrote: >> >> > Instead, of i and j >> >> > would *(a + 20 - 15) still have >> >> > undefined behaviour ? Probably any C compiler >> >> > will evaluate 20 - 15 during translation, but >> >> > does the standard require constant expression >> >> > to be evaluated during translation >> >> > even if it is a sub-expression >> >> > as in the above case ? >> >> >> >> No, it does not. It would be an unusual compiler that failed to do so, >> >> but it is not required. > > Yes, I got that, that's why I deleted my post immediately > after posting. How were you able to see it ? > How > By looking carefully.....
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| From | falk@rahul.net (Edward A. Falk) |
|---|---|
| Date | 2012-12-11 00:48 +0000 |
| Message-ID | <ka5vt2$lq6$2@blue-new.rahul.net> |
| In reply to | #29137 |
In article <232fe1b0-d8fa-42e2-85d8-12bcba97a4a1@googlegroups.com>, Prathamesh Kulkarni <bilbotheelffriend@gmail.com> wrote: > >Yes, I got that, that's why I deleted my post immediately >after posting. How were you able to see it ? >How News servers are not required to honor cancels, and many do not. Also, cancels can take time to propagate through the network, so previous poster could have seen your article and responded to it before it was deleted. -- -Ed Falk, falk@despams.r.us.com http://thespamdiaries.blogspot.com/
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| From | glen herrmannsfeldt <gah@ugcs.caltech.edu> |
|---|---|
| Date | 2012-12-10 21:01 +0000 |
| Message-ID | <ka5ik6$o40$1@speranza.aioe.org> |
| In reply to | #29136 |
James Kuyper <jameskuyper@verizon.net> wrote:
> On 12/10/2012 03:04 PM, Prathamesh Kulkarni wrote:
>> Instead, of i and j
>> would *(a + 20 - 15) still have
>> undefined behaviour ? Probably any C compiler
>> will evaluate 20 - 15 during translation, but
>> does the standard require constant expression
>> to be evaluated during translation
>> even if it is a sub-expression
>> as in the above case ?
> No, it does not. It would be an unusual compiler that
> failed to do so, but it is not required.
Well, constant expressions in context where constants
are needed are required to be evaluated at compile time,
but this (whole) expression isn't constant.
In Fortran 66 and 77 you couldn't
DIMENSION X(10+10)
but in C you always could. (Not counting VLAs)
It used to be suggested that one write Fortran constants with
the appropriate type, such as 0.0 instead of 0, to avoid
run-time conversion. One hoped that compilers would figure it
out, but you were never quite sure enough.
-- glen
>
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| From | Ken Brody <kenbrody@spamcop.net> |
|---|---|
| Date | 2012-12-12 14:24 -0500 |
| Message-ID | <kaalki$3uf$1@dont-email.me> |
| In reply to | #29136 |
On 12/10/2012 3:29 PM, James Kuyper wrote: > On 12/10/2012 03:04 PM, Prathamesh Kulkarni wrote: >> Instead, of i and j >> would *(a + 20 - 15) still have >> undefined behaviour ? Probably any C compiler >> will evaluate 20 - 15 during translation, but >> does the standard require constant expression >> to be evaluated during translation >> even if it is a sub-expression >> as in the above case ? > > No, it does not. It would be an unusual compiler that failed to do so, > but it is not required. When I went to college, there was a FORTRAN compiler aimed specifically at teaching FORTRAN programming. Since it was expected that there would be more time spent compiling (and recompiling, after fixing errors) the program than in running it (the resulting program would in all likelihood be run only once), there was zero optimization done on the resulting code. This made the compiler itself "lean and mean", allowing it to finish compiling (or getting to the errors) faster. It didn't make sense to spend X amount of time optimizing a program, only to save less than X time once the program actually ran the one time it would be run. I could see such an implementation of C being developed.
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| From | Robert Wessel <robertwessel2@yahoo.com> |
|---|---|
| Date | 2012-12-12 14:34 -0600 |
| Message-ID | <24qhc89qrvbhj8q2fngc65ee29cj9i1u49@4ax.com> |
| In reply to | #29173 |
On Wed, 12 Dec 2012 14:24:05 -0500, Ken Brody <kenbrody@spamcop.net> wrote: >On 12/10/2012 3:29 PM, James Kuyper wrote: >> On 12/10/2012 03:04 PM, Prathamesh Kulkarni wrote: >>> Instead, of i and j >>> would *(a + 20 - 15) still have >>> undefined behaviour ? Probably any C compiler >>> will evaluate 20 - 15 during translation, but >>> does the standard require constant expression >>> to be evaluated during translation >>> even if it is a sub-expression >>> as in the above case ? >> >> No, it does not. It would be an unusual compiler that failed to do so, >> but it is not required. > >When I went to college, there was a FORTRAN compiler aimed specifically at >teaching FORTRAN programming. Since it was expected that there would be >more time spent compiling (and recompiling, after fixing errors) the program >than in running it (the resulting program would in all likelihood be run >only once), there was zero optimization done on the resulting code. This >made the compiler itself "lean and mean", allowing it to finish compiling >(or getting to the errors) faster. It didn't make sense to spend X amount >of time optimizing a program, only to save less than X time once the program >actually ran the one time it would be run. Good old Watfor and Watfiv... In addition to doing no optimization (although the IBM compiler did little or none in basic mode), it allowed you to skip the heavyweight link step. I remember on a 370/138 (maybe it was a 4341 by that point, memories fade), typical student jobs (~100 cards in first semester Fortran), taking a couple of seconds of CPU time, whereas the IBM compiler took half a minute. Better diagnostics too. >I could see such an implementation of C being developed. But on what current platform would student size jobs take too long to compile, with or without optimization turned on?
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| From | glen herrmannsfeldt <gah@ugcs.caltech.edu> |
|---|---|
| Date | 2012-12-12 20:45 +0000 |
| Message-ID | <kaaqcg$gko$1@speranza.aioe.org> |
| In reply to | #29173 |
Ken Brody <kenbrody@spamcop.net> wrote: (snip on expression evaluation order) > When I went to college, there was a FORTRAN compiler aimed specifically at > teaching FORTRAN programming. Since it was expected that there would be > more time spent compiling (and recompiling, after fixing errors) the program > than in running it (the resulting program would in all likelihood be run > only once), there was zero optimization done on the resulting code. This > made the compiler itself "lean and mean", allowing it to finish compiling > (or getting to the errors) faster. It didn't make sense to spend X amount > of time optimizing a program, only to save less than X time once the program > actually ran the one time it would be run. Maybe about that time, there was a story about benchmarks for Fortran compilers. There was one that evaluated many complicated expressions, mostly using statement functions. This benchmark was then given to the OS/360 Fortran H compiler with optimization level of 2, where it compiled very slowly and ran in pretty much no time at all. It turns out that the compiler expands statement functions inline (seems to have been rare at the time), and then evaluates constant expressions. The compiler did the whole calculation down to one number to print out! > I could see such an implementation of C being developed. The favorite Fortran compilers I knew of for student programs were WATFOR and WATFIV. Both are in-core compilers. They don't write out an object program, but instead generate instructions in memory, ready to run. I believe that there is a WAT-C, but don't know anything about it. The WATCOM compilers don't seem to be in-core compilers. I do remember MS had a Quick-C which might have been (and still be) an in-core compiler. -- glen
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| From | Robert Wessel <robertwessel2@yahoo.com> |
|---|---|
| Date | 2012-12-12 15:29 -0600 |
| Message-ID | <vithc8t9dfnam01bngfoaa6i9u2imu6sig@4ax.com> |
| In reply to | #29180 |
On Wed, 12 Dec 2012 20:45:04 +0000 (UTC), glen herrmannsfeldt <gah@ugcs.caltech.edu> wrote: >Ken Brody <kenbrody@spamcop.net> wrote: > >(snip on expression evaluation order) > >> When I went to college, there was a FORTRAN compiler aimed specifically at >> teaching FORTRAN programming. Since it was expected that there would be >> more time spent compiling (and recompiling, after fixing errors) the program >> than in running it (the resulting program would in all likelihood be run >> only once), there was zero optimization done on the resulting code. This >> made the compiler itself "lean and mean", allowing it to finish compiling >> (or getting to the errors) faster. It didn't make sense to spend X amount >> of time optimizing a program, only to save less than X time once the program >> actually ran the one time it would be run. > >Maybe about that time, there was a story about benchmarks for Fortran >compilers. There was one that evaluated many complicated expressions, >mostly using statement functions. > >This benchmark was then given to the OS/360 Fortran H compiler with >optimization level of 2, where it compiled very slowly and ran in >pretty much no time at all. > >It turns out that the compiler expands statement functions inline >(seems to have been rare at the time), and then evaluates constant >expressions. The compiler did the whole calculation down to one >number to print out! > >> I could see such an implementation of C being developed. > >The favorite Fortran compilers I knew of for student programs were >WATFOR and WATFIV. Both are in-core compilers. They don't write out >an object program, but instead generate instructions in memory, ready >to run. > >I believe that there is a WAT-C, but don't know anything about it. > >The WATCOM compilers don't seem to be in-core compilers. > >I do remember MS had a Quick-C which might have been (and still be) >an in-core compiler. QuickC was MS's IDE, a precursor to Visual C++ and Visual Studio. Under the hood it used the contemporary MSC compilers.
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| From | glen herrmannsfeldt <gah@ugcs.caltech.edu> |
|---|---|
| Date | 2012-12-13 02:02 +0000 |
| Message-ID | <kabcuu$t5a$1@speranza.aioe.org> |
| In reply to | #29186 |
Robert Wessel <robertwessel2@yahoo.com> wrote: (snip, I wrote) >>I do remember MS had a Quick-C which might have been (and still be) >>an in-core compiler. > QuickC was MS's IDE, a precursor to Visual C++ and Visual Studio. > Under the hood it used the contemporary MSC compilers. I had one, as it came with the MSC compiler, but don't think I ever used it. Still, I always thought it had a different compiler inside. Maybe not a lot different. -- glen
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| From | Malcolm McLean <malcolm.mclean5@btinternet.com> |
|---|---|
| Date | 2012-12-17 05:57 -0800 |
| Message-ID | <fd284b6d-c843-4024-a4ed-a3d52c470ca2@googlegroups.com> |
| In reply to | #29173 |
On Wednesday, December 12, 2012 7:24:05 PM UTC, Ken Brody wrote: > On 12/10/2012 3:29 PM, James Kuyper wrote: > > When I went to college, there was a FORTRAN compiler aimed specifically at > teaching FORTRAN programming. Since it was expected that there would be > more time spent compiling (and recompiling, after fixing errors) the program > than in running it (the resulting program would in all likelihood be run > only once), there was zero optimization done on the resulting code. This > made the compiler itself "lean and mean", allowing it to finish compiling > (or getting to the errors) faster. It didn't make sense to spend X amount > of time optimizing a program, only to save less than X time once the program > actually ran the one time it would be run. > Sometimes when you're developing code, you need to know that it's correct. Other times you need to know that it's correct and fast enough. For instance if you are developing a video game, then typically you'll write a bit of code, then run the game to see what effect your changes have on the player's experience. So normally the program will have to run at the same speed the end-user will be receiving.
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| From | pete <pfiland@mindspring.com> |
|---|---|
| Date | 2012-12-10 20:20 -0500 |
| Message-ID | <50C68A6C.50DE@mindspring.com> |
| In reply to | #29134 |
Prathamesh Kulkarni wrote: > > Instead, of i and j > would *(a + 20 - 15) still have > undefined behaviour ? Probably any C compiler > will evaluate 20 - 15 during translation, but > does the standard require constant expression > to be evaluated during translation > even if it is a sub-expression > as in the above case ? (20 - 15) isn't a subexpression in the above case. (a + 20 - 15) means (a + 20) - 15 -- pete
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