Compiling 64-bit mpir using VC++ 2008 Express

MPIR is a Windows-friendly fork of GMP. It can be used as a direct replacement of GMP. I wanted to have my pycrypto build use _fastmath, and that meant having GMP support.

Building a 64-bit version of MPIR is fully supported in Visual C++ 2010 Express. Not so, alas, for Visual C++ 2008 Express. The MPIR build.vc9 readme flatly states “the Express Edition cannot build 64bit binaries”.

Game over? No Python-compatible MPIR lib?

Luckily, the MPIR devs worked hard and provided command-line tools in build.vc9. Using those, even an Express edition of VC++ 2008 can build 64-bit MPIR binaries.

Preparing to compile:

  • You now also need the Windows SDK so you have the amd64 compiler, which isn’t included in the Express version. This needs to be the Win7 + Net 3.5 SDK, not the Win7 + Net 4.0 SDK. You can find it here: , and again download  the ISO (the one for amd64 support though!) if nervous it may disappear. Install and make sure you install the “Visual C++ Compilers”.
  • The vcvarsall.bat in VC++ 2008 Express looks for the amd64 vcvars64.bat in all the wrong places. The easiest way to work around that is to navigate to the VC\bin directory of your VC++ 2008 installation (in my case C:\Program Files (x86)\Microsoft Visual Studio 9.0\VC\bin). Copy vcvars64.bat, and paste into the VC\bin\amd64 subdirectory. Next, rename VC\bin\amd64\vcvars64.bat to VC\bin\amd64\vcvarsamd64.bat.
  • You need yasm.exe to compile the assembly code in MPIR. Download the 64-bit version of yasm, rename the executable to yasm.exe, and copy it to the VC\bin directory of your VC++ 2008 installation.
  • You need the yasm.rules file. Download the MPIR source tarball, and copy yasm.rules from the build.vc9 directory. It goes into your VCProjectDefaults directory (in my case C:\Program Files (x86)\Microsoft Visual Studio 9.0\VC\VCProjectDefaults).
  • If you want to be able to automate the MPIR tests (that’s a really good idea), install Python. Chances are you are doing all this to use MPIR with Python and so it’s already installed. Just saying.


  • From within the directory, run configure. You can specify –cpu-x86_64 if you’d like to build a generic 64-bit library, rather than one specific to your CPU type. You may opt to specify –enable-shared if you want to build a DLL rather than a static library.
  • Run make

Check that the compiled library works correctly:

  • Run make check

Your libraries and include files will be in build.vc9\lib or build.vc9\dll, depending. You can now copy those to your VC\lib (.lib and .pdb files) and VC\include (.h files) directories, respectively. If you are looking to use the library with pycrypto, you’ll also want to copy mpir.lib to your Python installations \libs directory, since that is where will look for it. Well actually looks for gmp.lib – I’ll leave that as an exercise to the reader.

Additional speed.exe and try.exe utilities:

  • Run make speed
  • Run make try

These will be in build.vc9\x64\Release and build.vc9\try\x64\Release respectively and allow you to measure the speed of the MPIR library and test MPIR functions.


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