Opened 8 years ago
Closed 8 years ago
#17819 closed enhancement (fixed)
Use unsigned long for Integer.divisors
Reported by:  Jeroen Demeyer  Owned by:  

Priority:  minor  Milestone:  sage6.6 
Component:  c_lib  Keywords:  
Cc:  Merged in:  
Authors:  Jeroen Demeyer  Reviewers:  François Bissey 
Report Upstream:  N/A  Work issues:  
Branch:  1194cb7 (Commits, GitHub, GitLab)  Commit:  1194cb75acb96340b16f9a256aa55e0a3c2eb38c 
Dependencies:  #17794, #10257  Stopgaps: 
Description (last modified by )
The divisors
method of Integer
is implemented using long long
if possible. However, it would be better to use unsigned long
for this. One advantage is that we no longer need the mpz_set_longlong()
functions from c_lib
. This will also be faster for small inputs on 32bit systems. On 64bit systems, there should be no speed difference (except perhaps a small speedup due to skipping the mpz_longlong
overhead and the fact that we use 64 instead of 63 bits).
Change History (28)
comment:1 Changed 8 years ago by
Description:  modified (diff) 

comment:2 Changed 8 years ago by
Branch:  → u/jdemeyer/ticket/17819 

comment:3 Changed 8 years ago by
Commit:  → fae8cecadc86555f7962a903bb686f2727ff2f58 

Status:  new → needs_review 
comment:4 Changed 8 years ago by
Commit:  fae8cecadc86555f7962a903bb686f2727ff2f58 → 6f851b9eb96f73930aa265673679434eecfac6a6 

Branch pushed to git repo; I updated commit sha1. Last 10 new commits:
6ba47f0  Merge remotetracking branch 'origin/develop' into ticket/10257

307e526  Revert raise MemoryError changes from #12212

cd8407b  Merge branch 'ticket/12212_revert_raise' into ticket/10257

fa0612d  Merge remotetracking branch 'origin/develop' into ticket/10257

c561e2e  Fix check_allocarray() failure doctest on OS X

6650ca7  Add csage dependencies in Makefile

c37e933  Merge ticket/17794 into ticket/10257

352ffb8  Remove check for 1

5e3901d  Merge ticket/10257 into ticket/17819

6f851b9  Use check_allocarray() to allocate array

comment:5 Changed 8 years ago by
Dependencies:  → #17794, #10257 

comment:6 Changed 8 years ago by
Commit:  6f851b9eb96f73930aa265673679434eecfac6a6 → 3bc79b71b49aa37b7307174f29e228a6c2bc81f6 

Branch pushed to git repo; I updated commit sha1. New commits:
3bc79b7  Merge remotetracking branch 'origin/develop' into ticket/17819_

comment:7 Changed 8 years ago by
That sucks. mpz_set_ux isn't in gmp  at least gmp 5.1.3, if you know it is in 6.0.0+ I at least can force an upgrade in sageongentoo. But right now it is a major headache for sageondistro (much more so than pari git master).
comment:8 Changed 8 years ago by
Indeed, those functions seem MPIRspecific. For me personally, that's not an issue (we do use MPIR after all in Sage).
comment:9 Changed 8 years ago by
I know it would be less of an issue if other gmp using code had moved to using mpir directly one way or another (flint being the only one) rather than just saying "you can do that if mpir is installed with gmpcompat". I think I can do an ugly hack for that one.
comment:10 followup: 11 Changed 8 years ago by
You mean there would be less an issue if more code relied on MPIR?
comment:11 Changed 8 years ago by
Replying to jdemeyer:
You mean there would be less an issue if more code relied on MPIR?
Well that would force the hand.
What I mean is take pari. You can compile it with mpir by using the gmp compatibility layer. You cannot tell pari to compile directly against mpir, using mpir headers and libmpir.
If all the packages in the sage stack could do that. It would be easy, install mpir and build everything against it. Reality is everything apart from flint is using gmp and expect gmp. And only use mpir if it is masquerading itself as gmp.
In a distro where gmp is already installed because of gcc it won't happen unless you can convince the toolchain team of the distro to switch to mpir. Tough job.
comment:12 followup: 13 Changed 8 years ago by
We could also replace uintmax_t
by unsigned long
which is usually the same on 64bit systems and which doesn't have portability issues.
comment:13 followup: 14 Changed 8 years ago by
Replying to jdemeyer:
We could also replace
uintmax_t
byunsigned long
which is usually the same on 64bit systems and which doesn't have portability issues.
I guess that would be handy but what happens on 32 bits systems? We are still dealing with them for the foreseeable future.
I am trying a hack where integer.pyx and mpz.pxd explicitly use mpir. But not anything else.
I am guessing if mpir is a complete superset of gmp I could switch the whole sage library to explicit mpir. A bit of linking madness but it would work.
comment:14 Changed 8 years ago by
Replying to fbissey:
Replying to jdemeyer:
We could also replace
uintmax_t
byunsigned long
which is usually the same on 64bit systems and which doesn't have portability issues.I guess that would be handy but what happens on 32 bits systems?
When using unsigned long
, stuff would become slower for 32bit systems. It's really a matter of what do you prefer? It's a classical pick 2 out of 3: clean code, fast code, portable code.
comment:15 Changed 8 years ago by
New hurdle, my hack didn't work because I have mpir 2.6.0 installed, I am guessing the symbol is in 2.7.0. I would have to update mpir as well to make it work.
Yes classic! And it would be nice if it was completed by 6.6 release. Portable gets sageondistro out of the hole for this time but it may not go on forever. At some point mpir and gmp may diverge enough that flint or sage will want to do something that is mpir only. That day I think the best thing to do will be to make mpir explicit, at least where it is needed, rather than faking gmp. And pray that linker do their job properly.
comment:16 Changed 8 years ago by
Upgraded mpir but it still fails. Inspecting libmpir with
nm D /usr/lib64/libmpir.so.16  grep mpz_set_ux 000000000002ea6e T __gmpz_set_ux
And I get the same thing with mpir built in vanilla sage (and the gmp in sage) everything seems to be prefixed with __g
. Do you have an idea what is going on?
comment:17 Changed 8 years ago by
got it working by replacing every instances of gmp.h by mpir.h in sage/libs/gmp and replacing all gmp/gmpxx by mpir/mpirxx in module_list.py. Because c_lib, pari, ntl and friends are still linked to gmp I have linking to both gmp and mpir when inspecting with ldd, but readelf on the extension will only show mpir since it is the only one it is directly linked against.
Changing the headers in sage/libs/gmp wasn't enough in that it spread symbol problems in other places.
Now to run full doctest on the monster.
comment:18 followup: 19 Changed 8 years ago by
doctest run as normally as expected for sageongentoo on my machine. I was more or less expecting failures in the places where there are gmp(xx) headers outside of sage/libs/gmp but those seem to be more robust.
I would favor portability but that may be a discussion we need to have on sagedevel.
comment:19 followup: 20 Changed 8 years ago by
Replying to fbissey:
I would favor portability but that may be a discussion we need to have on sagedevel.
What do you think of my proposal to use unsigned long
? That would be portable and clean. On 64bit there would be no difference.
For small inputs, using unsigned long
will even be faster on 32bit systems, since the compiler wouldn't need to emulate 64bit long long
operations. For larger inputs, there might be a slowdown but it might not be so bad given that there are no native 64bit operations anyway.
comment:20 Changed 8 years ago by
Replying to jdemeyer:
Replying to fbissey:
I would favor portability but that may be a discussion we need to have on sagedevel.
What do you think of my proposal to use
unsigned long
? That would be portable and clean. On 64bit there would be no difference.For small inputs, using
unsigned long
will even be faster on 32bit systems, since the compiler wouldn't need to emulate 64bitlong long
operations. For larger inputs, there might be a slowdown but it might not be so bad given that there are no native 64bit operations anyway.
I am OK with using unsigned long
but it all gave me food for thought.
comment:21 Changed 8 years ago by
Description:  modified (diff) 

Status:  needs_review → needs_work 
Summary:  Use uintmax_t for Integer.divisors → Use unsigned long for Integer.divisors 
comment:22 Changed 8 years ago by
Description:  modified (diff) 

comment:23 Changed 8 years ago by
Commit:  3bc79b71b49aa37b7307174f29e228a6c2bc81f6 → 1194cb75acb96340b16f9a256aa55e0a3c2eb38c 

Branch pushed to git repo; I updated commit sha1. New commits:
1194cb7  Use unsigned long instead of uintmax_t for divisors()

comment:24 Changed 8 years ago by
Status:  needs_work → needs_review 

comment:25 followup: 26 Changed 8 years ago by
mpz_set_ux is still in that patch but it looks like it links ok ok against gmp. Rebuilding and testing, but it should be good.
comment:26 Changed 8 years ago by
Replying to fbissey:
mpz_set_ux is still in that patch but it looks like it links ok ok against gmp. Rebuilding and testing, but it should be good.
I left the declaration indeed, but it doesn't hurt...
comment:27 Changed 8 years ago by
Reviewers:  → François Bissey 

Status:  needs_review → positive_review 
Definitely doesn't, good to go.
comment:28 Changed 8 years ago by
Branch:  u/jdemeyer/ticket/17819 → 1194cb75acb96340b16f9a256aa55e0a3c2eb38c 

Resolution:  → fixed 
Status:  positive_review → closed 
New commits:
Use uintmax_t for Integer.divisors