Poly/ML

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720 discussions

type real in polyml
by immler＠in.tum.de 30 Oct '15

30 Oct '15

Hi David, Thanks for your answer, I should have subscribed to the polyml mailing list earlier. Using the SSE2 instructions and/or setting the intermediate precision to 64 bit would give a nice and clear semantics to floating point expressions in Poly/ML, so I would be very much looking forward to such a change. Best regards, Fabian > Am 07.10.2015 um 15:56 schrieb David Matthews <David.Matthews at prolingua.co.uk>: > > Hi Fabian, > This was a bit bizarre particularly as when I tried it on Windows there > didn't seem to be a problem. It is a problem with the precision and > when rounding occurs. Poly/ML uses the old x87 floating point unit on > both X86/32 and X86/64. As far as I'm aware all x86/64 machines support > the SSE2 instructions so other compilers use SSE2 instructions on 64-bit > but, by default use the x87 instructions on 32-bit. > > The x87 instructions use 80-bit registers internally and only round to > 64-bits when the registers are stored to double-precision values. The > SSE2 instructions are 64-bit so all the results are the same whether > values are stored to memory or not. The x87 has bits in the control > word that can allow it to compute intermediate results to 80-bit, 64-bit > or 32-bit precision. The question is whether this should be set to > 80-bit or 64-bits? > > Currently Poly/ML sets it to 80-bit precision at the start. As far as > I've been able to ascertain that is what other x86/32 compilers do. The > idea is, I suppose, to compute intermediate results to the best > precision available. It does, though, produce the strange results that > you've encountered. I think the reason for the difference in results is > whether the function can be computed at compile-time or not. > > I'm coming round to the view that it should instead set the FPU to > 64-bits so that intermediate results are the same whether they remain in > the register or are written out to memory and reloaded. It looks as > though the libraries in Visual C set that anyway which is why I only saw > the problem when I tested on Linux. This would also mean that results > would not change when, as I plan, I change to using the SSE2 > instructions on x86/64. > > Best regards, > David > > On 07/10/2015 14:07, Fabian Immler wrote: >> Hi David, >> >> Perhaps I should rephrase my enquiry to: "Do I get any guarantees from the implementation of type real in PolyML"? >> Naively, I would have expected, that every subexpression is evaluated according to the IEEE-754 standard (in double precision). >> >> I skimmed the implementation in libpolyml/reals.cpp, it looks like all intermediate results are stored in and retrieved from memory (real_arg, real_result). Is that sufficient to comply to IEEE-754? I.e., can there not occur "double rounding" (as in [1, section 3.3.1])? Or isn't there the need to use something like FLT_EVAL_METHOD=1 [2,3]? >> >> [1] http://www.springer.com/us/book/9780817647049 >> [2] https://en.wikipedia.org/wiki/C99#IEEE.C2.A0754_floating_point_support >> [3] http://www.cplusplus.com/reference/cfloat/ >> >> Best regards, >> Fabian >> >> >>> Am 07.10.2015 um 12:26 schrieb Fabian Immler <immler at in.tum.de>: >>> >>> Hi David, >>> >>> I noticed some strange behavior when working with type real in PolyML: >>> In the following example, where I have "testres = twosum a", depending on whether I call >>> "testres" or "twosum a" I get different results. >>> >>> If I take the definitions out of the structure Test, the results are the same. They are also the same if e.g. print-statements are inserted in between the assignments to b, s, sb and r. The results are also the same when evaluating inside Isabelle with the debugger turned on. >>> >>> Do you have an idea what is going on there? >>> Is it possible that some intermediate results are kept in higher precision in the FPU? >>> Does the compiler perform some "optimizations" on expressions of type real? >>> >>> Best regards, >>> Fabian >>> >>> >>> structure Test = struct >>> >>> fun one n = (if n = 0 then 100.0 else one (n - 1)); >>> >>> val a : real = one 1; >>> >>> fun twosum a = >>> let >>> val b = 1.0/1243313.0; >>> val s = a + b >>> val sb = s - b >>> val r = s - sb >>> in >>> r >>> end; >>> >>> val testres = twosum a; >>> end; >>> >>> open Test; >>> val a = twosum a >>> val b = testres >>> >>> >>>

2 1

Nested use
by David.Matthews＠prolingua.co.uk 21 Oct '15

21 Oct '15

There's long been an issue with "use" when trying to compile and run files which themselves contain "use". For example if ROOT.ML contains: use "first.ML"; use "second.ML"; The inner calls to "use" are taken relative to whatever the original working directory was set to, which means that ROOT.ML always has to be called with the right directory. It's not possible to call use "/home/david/mydirectory/ROOT.ML"; from an arbitrary directory. I've committed a change to the NestedUse branch which is one possible solution to this. The version of "use" in there records the full path to the parent directory of the file name when a file is "used". If that file then contains a nested call to "use" the file is first checked as previously using the original working directory but if that fails it looks for the name by appending the parent directory to the name given. So in the example above, it would first look for "./first.ML" and only if that does not exist would it look for "/home/david/mydirectory/first.ML". This seems as though it should achieve the desired effect with the minimum change to existing programs but there are other alternatives. For example, should it look first relative to the parent directory? David

3 4

compressing heap images
by Gerwin.Klein＠nicta.com.au 21 Oct '15

21 Oct '15

It turns out that with our collection of large Isabelle sessions that we run regularly, polyml heap image space is becoming a noticeable problem for us. To give an impression, we are now daily generating hundreds of gigabytes of polyml heap images. We do this on SSDs, because they reduce build times significantly. For SSDs, hundreds of gigabytes is still a large percentage of total capacity. Raf noticed recently that simple fast compression such as LZO/liblzo works really well for disk heap images. We?re getting a size reduction to about 27% at speeds of about 400MB/s. Initially I thought we might write a little wrapper that compresses/decompresses as polyml writes/reads these images, but it?s awkward, duplicates path logic etc. Would this be something worthwhile to include directly in the polyml heap dumping process instead? That way it would not just benefit us, but everyone who uses Isabelle and other polyml-based sessions on SSDs. Cheers, Gerwin ________________________________ The information in this e-mail may be confidential and subject to legal professional privilege and/or copyright. National ICT Australia Limited accepts no liability for any damage caused by this email or its attachments.

1 0

Profiling
by David.Matthews＠prolingua.co.uk 15 Oct '15

15 Oct '15

There has been some sort of profiling support in Poly/ML almost since the beginning. I have a feeling that the numbering system used in PolyML.profiling dates back to the old Poly language. There have been some recent changes to add support for yet another profiling mode, an option that profiles the time spent in a function but only for the calling thread, giving a way of separating out the work done in a multi-threaded application. It seemed like a good opportunity to revisit the whole thing. I've moved all aspects of profiling into a new structure PolyML.Profiling and removed the PolyML.profiling switch. The various options are now controlled by a datatype and there is a function "profile" that takes a mode, a function and an argument, runs the function by applying it the argument and prints the profile at the end. datatype profileMode = ProfileTime | ProfileAllocations | ProfileLongIntEmulation | ProfileTimeThisThread val profile = fn: profileMode -> ('a -> 'b) -> 'a -> 'b There are a couple of profiling modes that are a bit different since they print information about the state of the heap as the result of the previous computation. They are intended for use with PolyML.Compiler.allocationProfiling which causes the compiler to add extra information about where cells have been allocated. datatype profileDataMode = ProfileLiveData | ProfileLiveMutableData val profileData = fn: profileDataMode -> unit Finally there are additional versions of the functions that take an extra argument to enable an application (e.g. Isabelle) to capture the output from profiling. They take a function that is called with the unsorted list of counts and names. val profileDataStream = fn: ((int * string) list -> unit) -> profileDataMode -> unit val profileStream = fn: ((int * string) list -> unit) -> profileMode -> ('a -> 'b) -> 'a -> 'b David

1 0

incorrect canonical paths
by ramana＠member.fsf.org 15 Oct '15

15 Oct '15

Hi all, I just built Poly/ML fixes-5.2.2 (687b32704fdaffe013427962238482b786b666a4) fresh on a new machine with the following setup: uname -a Linux lemma 4.0.0-2-amd64 #1 SMP Debian 4.0.8-1 (2015-07-11) x86_64 GNU/Linux Now, if I go to a directory with non-lowercase name, I get a bad result: ramana at lemma:~$ mkdir TEST ramana at lemma:~$ cd TEST ramana at lemma:~/TEST$ poly Poly/ML 5.5.3 Testing > OS.Path.mkCanonical(OS.FileSys.getDir()); val it = "/home/ramana/test": string Why does Poly/ML think it is OK to lowercase filenames on this platform? Cheers, Ramana

2 2

tracing
by ramana＠member.fsf.org 13 Oct '15

13 Oct '15

Hi all, Does Poly/ML include any facility for tracing calls to (certain) functions? I am interested in generating a log of all calls to certain functions (including their arguments), in order, during the run of some program. Perhaps there is something in the profiler that can help with this? Cheers, Ramana

2 3

Using a finalizer with multiple arguments
by phil.clayton＠lineone.net 12 Oct '15

12 Oct '15

I am trying to create an SML binding to a C function that returns an array that the caller must free. Usually, there is a free function that takes just the array (as a pointer) which can be attached as a finalizer with CInterface.setFinal. I have encountered a case [1] where the caller must also pass the size of the array, returned when the array is created, to the free function. Simplifying the example, we have, for some C type Elem: Elem *new (..., int *n_elems); /* n_elems is an 'out' parameter */ void free (Elem *elems, int n_elems); and want an SML function like val new : ... -> elem vector Unfortunately, the function given to CInterface.setFinal is called with only one argument, the vol that is being finalized. Therefore this free function cannot be used. Does the current FFI architecture allow a variant of setFinal that passes extra arguments to the finalization function? For example: val setFinal1 : sym -> 'a Conversion -> vol -> 'a -> unit This isn't particularly common so is probably not a show-stopper. Another benefit could be enabling use of functions g_slice_alloc and g_slice_free1 that needs the number of bytes to free: https://developer.gnome.org/glib/stable/glib-Memory-Slices.html Thanks, Phil 1. The C function in question is gtk_target_table_new_from_list that returns an array and its size. The array should be freed with gtk_target_table_free which should be passed the size. See: - https://developer.gnome.org/gtk3/stable/gtk3-Selections.html#gtk-target-tab… - https://developer.gnome.org/gtk3/stable/gtk3-Selections.html#gtk-target-tab…

4 21

New Foreign Function Interface
by artella.coding＠googlemail.com 12 Oct '15

12 Oct '15

Hi, I was trying out the new foreign function interface that was committed today, and I find that if one tries to load a symbol that does not exist no error message is returned. For example in https://github.com/polyml/polyml/blob/598ff7841e5e155c1fff89bf75cd2a91ee779… if I do val sumTree2 = call1 ( getSymbol mylib "SumTreeDoesNotExist" ) cTree cInt; then no error message is reported. Then upon the call to sumTree aTree; an error is encountered and the program just terminates. Thanks

2 8

InternalError: AllocStore found but last allocation not complete
by phil.clayton＠lineone.net 08 Oct '15

08 Oct '15

After integrating the new Finalizable module in a library, I am getting an internal error from the compiler: Exception- InternalError: AllocStore found but last allocation not complete raised while compiling This affects Poly/ML 5.5.2 and the very latest commit with the compiler rebuilt (twice). An example is attached showing this. I have reduced this as far as I can but still a few small library files are required. The file 'polyml.sml' is the top-level file that uses the other files. Regards, Phil

2 3

Weak references
by ramana＠member.fsf.org 08 Oct '15

08 Oct '15

Hello, I am interested in using Poly/ML's Weak structure ( http://polyml.org/documentation/Reference/Weak.html) for hash-consing. The documentation would perhaps suggest that this is not an intended use of Weak, so I'd like to ask the list whether it is suitable and, if not, whether there are alternatives. An abstract of the problem is as follows. For a certain datatype, t, we want there to be at most one copy of any value of type t created by applying a constructor to unique arguments. To achieve this, we implement "hash-consing" constructors for t, which check whether the desired value exists already and return it if so, and only otherwise create a new value. To be able to check which values exist already, we maintain a hash table of all existing values. To allow values to be garbage collected when they are no longer needed, we make the hash table store only weak references to the values. The Weak structure allows weak references to be made to other references, but not to other non-reference values. Thus, the values in the hash table can be of type (t ref option ref), as produced by Weak.weak, but not of type (t option ref). Thus, on the face of it, it seems like using Poly/ML's Weak implementation will require unnecessary references and indirections. Is that indeed the case, or is Poly/ML smart about avoiding unnecessary indirections somehow? For hash-consing, we are not using Weak in the way described in its documentation, wherein the contents of the reference don't matter and the reference itself is only used as a token to track an external resource. Is there, perhaps, an alternative interface to Poly/ML's garbage collector more suitable for hash-consing? Cheers, Ramana

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