MPFR (libmpfr-4.dll)

MPFR library built for Windows using msys2/mingw64

Prebuilt packages

The current prebuilt packages can be downloaded from dist/mpfr-3.1.5_gmp-6.1.2.

Note that libgcc is not shipped together with pacakges where libgmp-10.dll and libmpfr-4.dll have it as a runtime dependency. This is because I was so far unable to obtain sources from which were mingw32 and mingw64 toolchains built under msys2. For now you can perhaps use those available directly from the mingw64 project.

For x32 Windows there is libgcc_s_dw2-1.dll here.
For x64 Windows there is libgcc_s_seh-1.dll here.

How to build libmpfr-4.dll

0. Example build script

   If you already know what to do, here is an example build/build.sh script. You can adapt it if you like.

1. Install MSYS2 and mingw-w64.

   Follow their instruction manual, once you have setup pacman install required toolchains and other packages:

   pacman -S base-devel
   pacman -S mingw-w64-i686-toolchain #for compiling x32 binaries
   pacman -S mingw-w64-x86_64-toolchain #for compiling x64 binaries
   pacman -S lzip #for extracting gmp

2. Download GMP and MPFR source code

   Extract the source code folders, for example to c:\libs.
   For extracting .lz file you can use tar --lzip -xvf gmp-*.tar.lz.

3. Open the correct shell for the compilation

   This is by default MSYS2 64bit/MinGW 32-bit or MSYS2 64bit/MinGW 64-bit in the Windows startup menu.
   Check your gcc version by gcc -v. Note the compiler and the configuration flags there.

4. Compile gmp and mpfr

   The following example code uses /c/libs/x32 directory just as an example.

   cd /c/libs/gmp-* #or whichever version
   
   ./configure --enable-shared --disable-static --prefix=/c/libs/x32
   make clean #clean up, just to be sure
   make > build.log #you can check out the compilation process
   make check
   make install

   cd /c/libs/mpfr-*
   
   ./configure --enable-shared --disable-static --enable-thread-safe 
   	--with-gmp=/c/libs/x32 --prefix=/c/libs/x32
   make clean
   make > build.log
   make check
   make install

   You can read more on what those configure flags do by ./configure --help in respective folders.
   For now it is enough to know that:

   • --enable-shared produces a shared .dll file

   • --disable-static disables compilation of a static library
     This is especially important for gmp, which can not do both static and dynamic compilation at once.

   • --prefix=<path> is where the result is installed after the compilation
     This is set by default to --prefix=/mingw32 or --prefix=/mingw64 based on the shell running.

   • --with-gmp=<path> is how you can specify your custom path to gmp, if you do not use the default one
     I used this option because otherwise configure posted a warning about not matching version of gmp.h.

   Note if you have encountered error: gmp.h isn't a DLL: use --enable-static --disable-shared
   during mpfr compilation, as I have, it is because mingw64 is not picking up any installed gmp dll.

5. Dynamic linking

The compiled libmpfr-4.dll is dependent on these **runtime** libraries:

* **libgmp-10.dll**
* **libgcc_s_dw2-1.dll** or **libgcc_s_seh-1.dll** (x32 or x64)
* **libwinpthread-1.dll**

The compiled libgmp-10.dll depends on **libgcc** only in x32 version.

These dependencies have to be accessible at runtime, which can be done by either placing them:
* in your application's directory
* in the current working directory
* in the system directories
* in a directory specified by the PATH environment variable.

You can and should check all the runtime dependencies by `ldd /c/libs/x32/bin/libmpfr-4.dll`
<br>or by the [Dependency Walker](http://dependencywalker.com/) Windows tool.

More information can be found here:
<br>https://msdn.microsoft.com/en-us/library/7d83bc18.aspx
<br>https://msdn.microsoft.com/en-us/library/windows/desktop/ms682586(v=vs.85).aspx

2. Static linking

If you wish to modify libmpfr-4.dll or libgmp-10.dll to link libgcc or libwinpthread statically,
<br>you can use linking options `-static-libgcc` and `-Wl,Bstatic -lpthread` respectivelly.

However, you can learn from [GMP Known Build Problems](https://gmplib.org/manual/Known-Build-Problems.html#Known-Build-Problems) page that libtool strips those options. To circumvent the problem they suggest appending them directly to the compiler variable. 

```bash
./configure CC="gcc -static-libgcc"
```

For MPFR build you can reuse a linking command from the build.log:

```bash
cd /c/libs/mpfr-*
cmd=$(grep -o 'gcc -shared.*' build.log) #store the linking command
cmd+=" -static-libgcc"
cmd+=" -Wl,-Bstatic -lpthread" #for libwinpthread
(cd src && $cmd) # execute cmd from src directory
make install
```

License information

• GNU Compiler Collection (GCC), which libgcc is a part of, is distributed under GNU GPL 3+
  with GCC Runtime Library Exception. The runtime library exception is described in this rationale.
  As a result libraries linked statically to libgcc do not have any license restrictions,
  provided they are elegible to the exception.

• mingw-w64 GCC for Windows 64 & 32 bits states that it license is disclosed along with its sources and is permissive.
  This information is well hidden on their webpage in the support section.
  This also applies to winpthread library or libwinpthread-1.dll (not to confuse with POSIX Threads for Windows or pthread-win32).
  In binary distributions of msys2/mingw64 targeting x86 and x64 you can find under mingw32 or mingw64 a file licenses/mingw-w64/COPYING that states:

  With exception of certain parts that are prominently marked as being
  in the Public Domain, BSD, or LGPL this Software is provided under the
  Zope Public License (ZPL) Version 2.1.

  Also of note should be COPYING.MinGW-w64.txt and COPYING.MinGW-w64-runtime.txt where the first also states:

  The idea is that if you create binary packages of your software with MinGW-w64, you can simply copy COPYING.MinGW-w64-runtime.txt into your package to fulfill the license requirements of the MinGW runtime.

  A separate license notice for winpthread is located in licenses/winpthread/COPYING.
  It seems fairly permissive, though it requires you to copy the notice and mentions having a part of posix-win32:

  Parts of this library are derived by:
  Posix Threads library for Microsoft Windows

• The GNU Multiple Precision Arithmetic Library (GMP) uses dual licensing under GNU LGPL v3 and GNU GPL v2.

• The GNU MPFR Library is licensed under GNU LGLP v3.

  LGLPv3 and GPLv2 impose requirements on source code distribution alongside binary distributions. The safest option is to simply distribute the source code with the provided binary distribution, because any other option usually results in long-term obligations.

  Note that mingw64 distribution also contains licenses/gmp and licenses/mpfr, because mingw64 ships with some version of GMP and MPFR. This shows what license notices must be provided in such case.

  You can read it all for yourself (though check your sanity first).